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Laser anemometer surveys were made of the 3-D flow field in NASA rotor 67, a low aspect ratio transonic axial-flow fan rotor. The test rotor has a tip relative Mach number of 1.38. The flowfield was surveyed at design speed at near peak efficiency and near stall operating conditions. Data is presented in the form of relative Mach number and relative flow angle distributions on surfaces of revolution at nine spanwise locations evenly spaced from hub to tip. At each spanwise location, data was acquired upstream, within, and downstream of the rotor. Aerodynamic performance measurements and detailed rotor blade and annulus geometry are also presented so that the experimental results can be used as a test case for 3-D turbomachinery flow analysis codes.

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A numerical study is carried out to investigate the effect of the addition of winglet to the end of blade on the axial fan performance. Validation and assessment of the used computer program FLUENT 6.2, is carried out by comparing its result with previous researcher. Simulation is then carried out to analyze the flow pattern with and without a winglet attached to the fan blade. Velocity distribution produced numerically showed that the winglet suppresses the secondary flow at the tip gap. Pressure distributions also confirmed the winglet advantages. Calculated performance of the fan used showed general increase of the fan efficiency with 3.5% above those without winglet at the optimum efficiency point and with up to 6 % at off design point.

A theory is presented for the discrete-frequency sound radiated by axial-flow fans and compressors. The theory is based on the noise radiation from the fluctuating forces on either a rotor or a stator stage due to interactions with upstream components. The model used is a cascade of point forces, one on each blade, radiating into free air. It appears that, provided that the correct phase relations are retained, this model may be expected to give accurate predictions of farfield noise even for long, hard-wall duct cases. Both over-all power and directionality curves for the sound radiation are presented, and methods are given for calculating the fluctuating forces acting from the wake geometry. Once wake geometry is defined, the theory enables one to perform calculations of the noise observed at any point. Preliminary agreement with experiment is demonstrated. Virtually all significant compressor design parameters can be included in the theory, and therefore it appears that the theory could be used in tradeoff studies to minimize noise at the preliminary design stage of an engine.

The application of improved blade tip geometries is studied with the aim of identifying an effective design concept for industrial fan passive noise control. The concept developed optimizes a datum blade by means of profiled endplates at the tip, reducing fan noise by changing the tip leakage flow behaviour. Experimental and computational investigations have been carried out on a family of axial fans, in fully ducted configuration, to establish the aerodynamic merits of the proposed blade tip design concept. The flow mechanisms in the fan tip region are correlated to specific blade design features that promote a reduction of the fan aero-acoustic signature in both tonal and broadband noise components. The tip vortical flow structures are characterized, and their role in creation of overall stage acoustic emissions clarified. The reported research identifies modification of tip geometry as markedly affecting the multiple vortex behaviour of blade tip leakage flow by altering the near-wall fluid flow paths on both blade surfaces. Blade tip endplates were also demonstrated to influence the rotor loss behaviour in the blade tip region. Improvement of rotor efficiency was correlated to the control of tip leakage flows.

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A detailed literature survey is presented herein in order to overview the aerodynamic impact of non-radial blade stacking techniques applied to axial flow fan and compressor rotors. The literature suggests a consensus that forward blade sweep and skew provides a means for the following advantages in the part load operational range of low-speed axial flow turbofan and compressor rotors: improvement of efficiency and performance, and extension of stall-free operating range. However, the published research results are rather diversified regarding the judgment of performance and loss modifying effects of sweep and skew at the design point. The current paper summarizes the major aerodynamic phenomena related to such blade stacking techniques, in order to contribute to a general reasoning of performance and efficiency modification at the design flow rate. Furthermore, it provides guidelines how to consider these phenomena in tailoring the blade geometry for potential efficiency gain and for achievement of the prescribed total pressure rise at the design point. The role of adequate computational fluid dynamics tools was considered in the paper to be essential in evaluation of aerodynamic effects of non-radial blade stacking, as well as in incorporation of sweep and skew in systematic blade design techniques.

A joint experimental and numerical study has been achieved on a low-speed axial ring fan in clean inflow. Experimental evidence shows large periodic broadband humps at lower frequencies than the blade passing frequencies and harmonics even at design conditions. These sub-harmonic humps are also found to be sensitive to the fan process and consequently to its tip geometry. Softer fans yield more intense humps more shifted to lower frequencies with respect to the fan harmonics. Unsteady turbulent flow simulations of this ring fan mounted on a test plenum have been achieved by four different methods that have been validated by comparing with overall performances and detailed hot-wire velocity measurements in the wake. Noise predictions are either obtained directly or are obtained through Ffowcs Williams and Hawkings' analogy, and compared with narrowband and third-octave power spectra. All unsteady simulations correctly capture the low flow rates, the coherent vortex dynamics in the tip clearance and consequently the noise radiation dominated by the tip noise in the low- to mid-frequency range. Yet, only the scale-adaptive simulation and the lattice Boltzmann method simulations which can describe most of the turbulent structures accurately provide the proper spectral shape and levels, and consequently the overall sound power level.

Induced draft fans extract coal fired boiler combustion products, including particles of un-burnt coal and ash. As a consequence of the particles, the axial fan blades’ leading edges are subject to erosion. Erosion results in the loss of the blade leading edge aerodynamic profile and a reduction of blade chord and effective camber that together degrade aerodynamic performance. An experimental study demonstrated that while the degradation of aerodynamic performance begins gradually, it collapses as blade erosion reaches a critical limit. This paper presents a numerical study on the evolution of blade leading edge erosion patterns in an axial induced draft fan. The authors calculated particle trajectories using an in-house computational fluid dynamic (CFD) solver coupled with a trajectory predicting solver based on an original finite element interpolation scheme. The numerical study clarifies the influence of flow structure, initial blade geometry, particle size, and concentration on erosion pattern.

The sound emission of low-pressure axial fans is substantially influenced by the fan blade geometry and the inflow conditions, induced by the fan installation system. However, the combined impact of these parameters has not yet been comprehensively investigated or understood. Hence the motivation for this thesis was to undertake a compact, systematic experimental study on the sound emission of axial fans with different blade geometry parameters under distorted inflow conditions. The impact of the fan blade design was investigated on the basis of nine fans with different blade loading distributions and different fan blade skew, but otherwise identical geometric parameters. Additionally, the effectiveness of leading edge serrations in reducing axial fan noise was examined with a parametric study of a generic flat-plate fan and eleven sets of fan blades with leading edge modifications that included single-sine (sinusoidal), double-sine and random amplitude leading edge serrations. The inflow conditions were altered to incorporate either an increased inflow turbulence intensity or an inhomogeneous inlet velocity profile. These conditions were realised by grids - three turbulence grids and two velocity gradient grids - that were mounted upstream of the fans. A large increase in the sound radiation with elevated tonal and broadband components was observed with the modified inflow conditions. Thereby, the sound emission of the forward-skewed fans showed a greater susceptibility for distorted inflow conditions than that of the backward-skewed fans. It was found that owing to the fan blade shape, the forward-skewed fans are prone to higher unsteady blade forces and increased pressure fluctuations on the fan blade leading edges. These factors determine the tonal and broadband sound radiation. For the backward-skewed and unskewed fans, dominant subharmonic components, originating from flow phenomena in the tip region, occurred under both free and distorted inflow conditions. All types of leading edge serrations achieved a sound reduction compared with the reference fan with straight leading edges - for both free and distorted inflow conditions. The greatest reduction was observed for the sinusoidal leading edges, followed by the double-sine and random amplitude leading edges. The reduction was mainly dependent on the serration wavelength rather than the serration amplitude: the smaller the leading edge wavelength, the greater was the overall sound reduction. Overall, the investigations showed that the sound emission of low-pressure axial fans is highly dependent on the combined impact of the fan blade geometry and the inflow conditions. The findings contribute to a better understanding of the sound generation mechanisms in axial fans and show means for designing low-noise fans in complex cooling or ventilation systems.

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The modeling capabilities of TURBO, an existing turbomachinery analysis code, have been extended to include the ability to solve the external and internal flow fields of a boundary-layer ingesting inlet. Flow solutions are presented and compared with experimental data for several high-Reynolds-number flows to validate the solver modifications. The upstream flowfield was coupled to a hypothetical compressor fan to present a fully developed distortion to the fan. Although the total pressure distortion upstream of the fan was symmetrical for this geometry, the pressure rise generated by the fan blades was not, because of the velocity nonuniformity of the distortion. Total pressure profiles at various axial locations are computed to identify the overall distortion pattern, how the distortion evolves through the blade passages and mixes out downstream of the blades, and where any critical performance concerns might be. Stall cells are identified that are stationary in the absolute frame and are fixed to the inlet distortion. Flow paths around the blades are examined to study the stall mechanism. Rather than a typical airfoil stall, it is observed that the nonuniform pressure loading in the radial direction promotes a three-dimensional dynamic stall. The stall occurs at a point of rapid incidence angle oscillation observed when a blade passes through a distortion and re-attaches when the blade sees more uniform flow outside the distortion.

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Erosion of compressor blades due to operation in particulate environments is a serious problem for the manufacturers and users of industrial and aeronautical gas turbines, because of drastic degradations in performance, mostly through blunting of blade leading edges, reduction of chord and increase of tip clearance and surface roughness. This paper presents a numerical study to assess the effects of erosion by sand ingestion on blade geometry deterioration and the subsequent performance degradation. These computations were carried out for an axial turbomachine in steps; first, calculations of particle trajectories and erosion resulting from cumulative impacts by sand particles (MIL-E 5007E, 0–1000 μm) were carried out, then, the required data were used in the estimation of performance degradation based on a mean-line method that included Lieblein and Koch-Smith loss correlations, in addition to an erosion fault model derived from blade geometry deterioration. This global procedure was successfully validated upon an axial fan stage, and can be generalized easily to other axial compressor designs.

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An axisymmetric, incompressible Navier-Stokes solver was developed to calculate the flow field of a ducted fan. The fan effect is modeled via the momentum source concept. The effects of the spinning fan blades were introduced into the flow field as time-averaged sources in the momentum equations. These source terms were not known a priori but are the result of the flow solution at each iteration. This approach simplified the modeling of the fan blades and provided a very rapid solution procedure for the flow problem. A new grid generator capable of recognizing the duct and nacelle geometry was developed and tested for several industrial ducted fans of current interest. Prediction of hover performance for a ducted fan model was calculated and compared with available wind tunnel test data. The comparison was good. Preliminary results showed that the Computational Fluid Dynamics (CFD) program could be used as an axial flow analysis tool for ducted fan design.

The problem of broadband noise generated by turbulence impinging on a downstream blade row is examined from a theoretical viewpoint. Equations are derived for sound power spectra in terms of 3 dimensional wavenumber spectra of the turbulence. Particular attention is given to issues of turbulence inhomogeneity associated with the near field of the rotor and variations through boundary layers. Lean and sweep of the rotor or stator cascade are also handled rigorously with a full derivation of the relevant geometry and definitions of lean and sweep angles. Use of the general theory is illustrated by 2 simple theoretical spectra for homogeneous turbulence. Limited comparisons are made with data from model fans designed by Pratt & Whitney, Allison, and Boeing. Parametric studies for stator noise are presented showing trends with Mach number, vane count, turbulence scale and intensity, lean, and sweep. Two conventions are presented to define lean and sweep. In the "cascade system" lean is a rotation out of its plane and sweep is a rotation of the airfoil in its plane. In the "duct system" lean is the leading edge angle viewing the fan from the front (along the fan axis) and sweep is the angle viewing the fan from the side (,perpendicular to the axis). It is shown that the governing parameter is sweep in the plane of the airfoil (which reduces the chordwise component of Mach number). Lean (out of the plane of the airfoil) has little effect. Rotor noise predictions are compared with duct turbulence/rotor interaction noise data from Boeing and variations, including blade tip sweep and turbulence axial and transverse scales are explored.

This paper describes the development and application of a novel mesh generator for the flow analysis of turbomachinery blades. The proposed method uses a combination of structured and unstructured meshes, the former in the radial direction and the latter in the axial and tangential directions, in order to exploit the fact that blade-like structures are not strongly three-dimensional since the radial variation is usually small. The proposed semi-structured mesh formulation was found to have a number of advantages over its structured counterparts. There is a significant improvement in the smoothness of the grid spacing and also in capturing particular aspects of the blade passage geometry. It was also found that the leading- and trailing-edge regions could be discretized without generating superfluous points in the far field, and that further refinements of the mesh to capture wake and shock effects were relatively easy to implement. The capability of the method is demonstrated in the case of a transonic fan blade for which the steady state flow is predicted using both structured and semi-structured meshes. A totally unstructured mesh is also generated for the same geometry to illustrate the disadvantages of using such an approach for turbomachinery blades. Copyright © 2000 John Wiley & Sons, Ltd.

Microscale axial flow fans were investigated in response to the growing cooling requirements of the electronics industry. The two main challenges of this investigation were manufacture of a fully functional fan at the microscale, and performance reduction due to Reynolds number effect. Manufacture of a fully functional axial microfan complete with three-dimensional blade geometry was proven possible using microelectrodischarge machining techniques. Experimental performance measurements proved that Reynolds number effect was not prohibitive at the microscale, and dimensional analysis thereof derived a novel linear scaling method, which quickly and accurately predicted the Reynolds number effect at any fan scale.

Energy conversion in squirrel-cage fans is sensitive to the inlet geometry. It occurs at the inlet where a separation zone which occupies a major volume in the rotor and the volute starts. In this research, different inlets of inward and outward types were tested on two fans. First, the inlet diamenter and position were matched with the rotor, which improved the fan characteristic curves. The results of the experiments were sensitive to the width of the blade retaining ring (shroud). Later the tangential and radial components of the velocity out of the rotor were measured. The resulting velocity profiles across the scroll width showed that outward inlets produce a more uniform velocity angle inside the volute than inward inlets did. This was not because of a more aerodynamic flow through the rotor blades by was due to a better match between the inlet and the volute. The axial energy transfer resulted in tangential velocities larger than the rotor velocity, at axial positions across the volute where there was no flow out of the rotor.

A major component of the noise in modern aeroengines is rotor–stator interaction noise generated when the wake from the rotating fan impinges on a stator row downstream. An analytically based model for the prediction of upstream-radiated rotor–stator interaction noise is described, and includes the important effect of mean swirling flow on both the rotor wake evolution and the acoustic response. The analytic nature of the model allows for the inclusion of all wake harmonics and enables the response at all blade passing frequencies to be determined. An asymptotic analysis based on large rotor blade number is used to model the evolution of the rotor wake downstream in a cylindrical duct carrying mean swirling flow. The equations governing the axial evolution of the wake simplify to three coupled first-order differential equations in the interior, while close to the duct walls, a boundary-layer correction is required in order to satisfy the impermeability conditions at the boundaries. At the stator location, the wake is used as input into a local linear cascade model at each radius. The interaction of each wake harmonic gives rise to acoustic waves of multiple azimuthal order which contribute to the pressure field radiated back upstream. This enables the total acoustic response to be determined in terms of cylindrical duct modes in mean swirling flow. The effect of stator blade geometry (thickness, camber, angle of attack) and rotor–stator separation on the total upstream-radiated noise is determined. Blade geometry is shown to have a significant effect on the noise generated, and increasing the rotor–stator gap can lead to large reductions in noise levels. Asymptotic treatment of the acoustic field, based on large azimuthal order, is also considered and used to identify the dominant contributions to the total pressure field resulting from the rotor–stator interaction. The ray structure of the acoustic modes in swirl is shown to be very different in some cases from that in uniform flow.

Variable pitch axial flow fans are widely used in industrial applications to satisfy variable operating conditions. The change of the blade pitch leads to a different rotor geometry and has a major influence on the unsteady operation of the machine. In this work, an experimental research on an axial flow fan with variable pitch blades has been carried out. First of all, the fan performance curves has been obtained. Then the flow field has been measured at ten radial locations both at the inlet and exit rotor plane using hot wire anemometry. Velocity components and total unsteadiness were determined and analyzed in order to characterize the influence of pitch blade and operating conditions on the flow structure.

Axial fans often show adverse flow conditions at the fan hub and at the tip of the blade. The modification of conventional axial fan blade is presented. Hollow blade was manufactured from the hub to the tip. It enables the formation of self-induced internal flow through internal passages. The internal flow enters the passage of the hollow blade through the opening near the fan hub and exits through the trailing edge slots at the tip of the hollow blade. The study of the influence of internal flow on the flow field of axial fan and modifications of axial fan aerodynamic characteristics is presented. The characteristics of the axial fan with the internal flow were compared to characteristics of a geometrically equivalent fan without internal flow. The results show integral measurements of performance testing using standardized test rig and the measurements of local characteristics. The measurements of local characteristics were performed with a hot-wire anemometry and a five-hole probe. Reduction in adverse flow conditions near the trailing edge at the tip of the hollow blade, boundary-layer reduction in the hollow blade suction side, and reduction in flow separation were attained. The introduction of the self-induced blowing led to the preservation of external flow direction defined by the blade geometry, which enabled maximal local energy conversion. The integral characteristic reached a higher degree of efficiency.

Numerical design optimization of the aerodynamic performance of axial fans is carried out, maximizing the efficiency in a design interval of flow rates. Tip radius, number of blades, and angular velocity of the rotor are fixed, whereas the hub radius and spanwise distributions of chord length, stagger angle, and camber angle are varied to find the optimum rotor geometry. Constraints ensure a pressure rise above a specified target and an angle of attack on the blades below stall. The optimization scheme is used to investigate the dependence of maximum efficiency on the width of the design interval and on the hub radius. [S0098-2202(00)01602-3]

Geometry analysis of the axial fan impeller, experimentally obtained operating characteristics and experimental investigations of the turbulent swirl flow generated behind the impeller are presented in this paper. Formerly designed and manufactured, axial fan impeller blade geometry (originally designed by Prof. Dr-Ing. Z. Protic?) has been digitized using a threedimensional (3D) scanner. In parallel, the same impeller has been modeled by beta version software for modeling axial turbomachines, based on modified classical calculation. These results were compared. Then, the axial fan operating characteristics were measured on the standardized test rig in the Laboratory for Hydraulic Machinery and Energy Systems, Faculty of Mechanical Engineering, University of Belgrade. Optimum blade impeller position was determined on the basis of these results. Afterwards, the impeller with optimum angle, without outlet vanes, was positioned in a circular pipe. Rotational speed has been varied in the range from 500 till 2500rpm. Reynolds numbers generated in this way, calculated for axial velocity component, were in the range from 0,8?105 till 6?105. LDA (Laser Doppler Anemometry) measurements and stereo PIV (Particle Image Velocimetry) measurements of the 3D velocity field in the swirl turbulent fluid flow behind the axial fan have been performed for each regime. Obtained results point out extraordinary complexity of the structure of generated 3D turbulent velocity fields.

The geometry design and machining of blades for axial-flow fans are important issues because the twisted profile and flowfield of blades are complicated. The rapid design of a blade that performs well and satisfies machining requirements is one of the goals in designing fluid machinery blades. In this study, an integrated approach combining computational fluid dynamics (CFD), an artificial neural network, an optimization method and a machining method is proposed to design a three-dimensional blade for an axial-flow fan. From the machining point of view, the three-dimensional surface geometry of a fan blade can be defined as the swept surface of the tool path created by using the generated machining method. By taking advantage of its powerful learning capability, a back-propagation artificial neural network is used to set up the flowfield models and to forecast the flow performance of the axial-flow fan. The desired optimal blade geometry is obtained by using a complex optimization method.

Experiments have been performed in a supersonic cascade facility to elucidate the fluid dynamic phenomena and loss mechanism of a strong shock-wave turbulent boundary layer interaction in a compressor cascade. The cascade geometry is typical for a transonic fan tip section that operates with a relative inlet Mach number of 1.5, a flow turning of about 3 deg, and a static pressure ratio of 2.15. The strong oblique and partly normal blade passage shock-wave with a preshock Mach number level of 1.42 to 1.52 induces a turbulent boundary layer separation on the blade suction surface. The free-stream Reynolds number based on chord length was about 2.7 × 106. Cascade overall performance, blade surface pressure distributions, Schlieren photographs, and surface visualizations are presented. Detailed Mach number and flow direction profiles of the interaction region (lambda shock) and the corresponding boundary layer have been determined using a Laser-2-Focus anemometer. The obtained results indicated that the axial blade passage stream sheet contraction (axial velocity density ratio) has a significant influence on the mechanism of strong interaction and the resulting total pressure losses.

Skewed blades in low-speed, low-pressure axial fans are becoming more and more popular. They seem to offer a noise reduction in such applications as heat exchange units etc. Many authors have described acoustical models which in some cases address entirely different noise generation mechanisms. First this paper gives a detailed survey of the mechanisms, models and results found in the literature. It becomes evident that no single mechanism explains the noise reduction in a rotor due to blade skew. This might cause the present lack of profound prediction methods for the noise reduction potential. The second part of the paper focuses on our own recent investigations of low-pressure fans with skewed blades. Some observations are reported which are based on numerically computed flow fields in rotors with skewed and unskewed blades and measurements. Compared to conventional or even backward skewed blades forward (i.e. in direction of rotation and/or against the flow direction) skew of the blades increases the flow in the hub region of the rotor which is usually endangered by flow separation. This seems to stabilize the flow field in the rotor because stall is shifted to remarkably low flow rates. Simultanously the radiated noise stays low in a large range of operation. At very high and low flow rates the noise is the same of both skewed and unskewed blades, i.e. it is independent of the blade's geometry.

The axial fan reaction and the vector diagram the work and flow coefficient diagram blade loading parameters blade geometry aspect ratio relative motion effects vortex flow Mach number effects Reynolds number effects compressible flow relationships the stage characteristic the repeating stage concept spanwise matching of high diameter ratio stages stall surge performance presentation stage matching and surge control inlet flow maldistribution rig testing stage performance prediction overall performance prediction performance with altered gas properties design of a domestic ventilator design of an industrial fan design of a transonic wind tunnel fan design of an industrial compressor design of a simple jet engine compressor HP compressor mid stage the high bypass fan.

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We report on the low noise optimization of an axial fan specifically designed for the cooling of CSP power plants. The duty point presents an uncommon combination of a load coefficient of 0.11, a flow coefficient of 0.23 and a static efficiency ηstat > 0.6. Calculated fan Reynolds number is equal to Re = 2.85 × 107. Here we present a process used to optimize and numerically verify the fan performance. The optimization of the blade was carried out with a Python code through a brute-force-search algorithm. Using this approach the chord and pitch distributions of the original blade are varied under geometrical constraints, generating a population of over 200000 different possible individuals. Each individual was then tested using an axisymmetric Python code. The software is based on a blade element axisymmetric principle whereby the rotor blade is divided into a number of streamlines. For each of these streamlines, relationships for velocity and pressure are derived from conservation laws for mass, tangential momentum and energy of incompressible flows. The final geometry was eventually chosen among the individuals with the maximum efficiency. The final design performance was then validated through with a CFD simulation. The simulation was carried out using a RANS approach, with the cubic k-ε low Reynolds turbulence closure of Lien et al. The numerical simulation was able to verify the air performance of the fan and was used to derive blade-to-blade distributions of design parameters such as flow deviation, velocity components, specific work and diffusion factor of the optimized blade. All the computations were performed in OpenFOAM, an open source C++- based CFD library.

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The paper presents a design procedure for anti-vortex end-plates that are fitted to tip limited blades of the subsonic axial fans utilised in compact cooling units. The authors study the impact of tip leakage vortex bursting on the performance of the studied class of fans. The vortex breakdown occurs in the swirling flows at a blade’s tip, and is found to be a flow feature associated with the production of fan acoustic emissions. The link between aerodynamic flow features in the blade tip region and fan acoustic emissions is exploited through a design process that aims to control the blade tip flow with the specific objective of reducing fan acoustic emissions. This noise-by-flow flow control design process is implemented by reconfiguring the end-plate at the blade tip using a multiple-vortex-breakdown criterion for the design of the end-plates. The aerodynamic and acoustic performance of the newly conceived end-plate design has been assessed and is compared with the performance of a fan with blades fitted with base-line end-plate geometry. The assessment of aerodynamic and acoustic performance utilises both numerical simulations of the flow-field in the blade tip region plus an experimental assessment of fan aerodynamic and acoustic performance. The reported research verified the technical merit of the developed passive noise control strategy, demonstrating that the control of blade tip leakage flow can result in a reduction in blade tip flow generated noise.

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Comparative strength analysis of two popular options of the radial centrifugal fan impeller design used in horizontal conveyor dryer for fine-grained raw materials is presented. Three types of materials for impeller manufacturing-ASTM A36 steel, Hardox 450 steel and aluminium alloy 6061-T6 are considered. The finite element method (FEM) has been used to investigate stresses and deformations of the impeller within the operational speed range. Analysis shows that the better design is the impeller made of Hardox 450 steel with a central disk. Although the maximum stress is slightly higher in the blades slot for central disk fitting for this design option, it has greatly reduced stresses in contact edges with two other disks (by 22-38%) and blades bending deformation (by 51%). For this design, the maximum operational rotation speed is 1135 min-1 according to the yield strength with a 15% safety factor, while for basic design, it is 1225 min-1. The rational choice of material depends on maximum value of the yield stress to density ratio as well as taking into account the operating conditions and required fan performance. Recommendations for manufacturing the centrifugal fan impeller related to chosen material are given.

Measurements of the three mean velocity components and five of the Reynolds stresses have been carried out in the blade passage of a centrifugal fan impeller. The impeller was of ordinary design, with nine backward curved blades, and all measurements were carried out at the design flow rate. The mean velocity measurements show that the flow can be characterized as an attached flow with almost linearly distributed velocity profiles. However, in a region near the suction side close to the shroud a low velocity region is created. From the turbulence measurements it can be concluded that relatively low values of the turbulent stresses are predominating in the center region of the channel. Closer to the walls higher values of the normal as well as shear stresses are noted.

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The objective of the present investigation is to explore the possibility of improving the performance of a centrifugal fan at low Reynolds numbers using a simple passive means, namely Gurney flap (GF). GFs of 1/<TEX>$8^{th}$</TEX> inch brass angle (3.175 mm) corresponding to 15.9% of blade exit height or 5.1% of blade spacing at the impeller tip are attached to the impeller blade tip on the pressure surface. Performance tests are carried out on the centrifugal fan with vaneless diffuser at five Reynolds numbers (viz., 0.30, 0.41, 0.55, 0.69, <TEX>$0.82{\times}10^5$</TEX>, i.e., at five speeds respectively at 1,100, 1,500, 2,000, 2,500 and 3,000 rpm) without and with GF. Static pressures on the vaneless diffuser hub and shroud are also measured for each speed at four flow coefficients [<TEX>${\phi}$</TEX>=0.23 (below design flow coefficient), <TEX>${\phi}$</TEX>=0.34 (design flow coefficient), <TEX>${\phi}$</TEX>=0.45 (above design flow coefficient) and <TEX>${\phi}$</TEX>=0.60 (above design flow coefficient)] with and without GF. From the performance curves it is found that the performance of the fan improves considerably with GFs at lower Reynolds numbers and improves marginally at higher Reynolds number. Similar improvements are observed for the static pressures on the diffuser hub and shroud. The effect of Reynolds number on the performance and static pressures is considerable. However the effect is reduced with GFs.

This paper deals with the determination of stress distribution for a centrifugal fan consists of back sheet, ten airfoil blades and shroud by using Finite element Packaged program (NSTRAN). The results showed that the blade trailing edge and the shroud plate have amaximum VonMises stress which exceeds the yield point of the materials. Thickness effect of each part on the stress distribution in the impeller was determined with fixing the other parts thickness.The result showed that the optimum thickness of the plate is (11mm), for shroud is (9mm) for blade is (3mm), for back sheet plate is (11mm) for shroud stiffener is (3mm). the overall results pointed out that the shroud plate is a critical part and has a large effect on the stress distribution than other parts. Keywords: Centrifugal Fan, VonMises stress, Finite Element, NASTRAN

This paper reports velocity measurement data in the interaction region between the impeller and vaned diffuser and the results of numerical flow simulation of the whole machine (impeller, vaned diffuser and volute) of a single stage centrifugal fan. Two-dimensional instantaneous velocity measurement is done using particle image velocimetry (PIV). Numerical simulation of impeller-diffuser-volute interaction is performed using CFX-Tascflow commercial code. A frozen rotor simulation model is used for the steady calculation and a rotor-stator simulation model is used for the unsteady calculation using the steady results as an initial guess. The simulation results show that the separated flow regime near the diffuser hub extends to the volute. Comparison between the unsteady computation and those of measurement indicates that the rotor/stator model employed in the simulation predicts essential characteristics of unsteady flow in the centrifugal fan. However, quantitative agreement remains rather poor.

Predicted and measured surface velocity and pressure distributions in the internal flow channels of a centrifugal fan impeller are presented for volume flow rates between 80 and 125 percent of design flow rate. Predictions are based on a fully three-dimensional, finite element analysis of the inviscid, incompressible blade channel flow. Additional predictions using a conventional quasi-three-dimensional analysis are presented for comparison. Experimental results were developed using extensive blade and sidewall surface pressure taps installed in a scale model of an airfoil-bladed centrifugal fan impeller designed for heavy industrial and power generation applications. The results illustrate the ability of both flow analyses to predict the dominant features of the impeller flow field, including peak blade surface velocities and adverse gradients at flows far from the design point. In addition, the experimental results provide valuable insight into the limiting channel diffusion values for typical centrifugal cascade performance, and the influence of viscous effects as seen in deviations from the ideal flow predictions.

In this study we present models for the parametric optimization of a centrifugal fan impeller using kriging-simulated annealing (SA) meta-algorithm. First, a kriging model is constructed using a limited number of CFD simulations for the centrifugal fan impeller to be optimized. The inlet and outlet blade angles are chosen to optimize the impeller. A dataset consisting of 22 different blade angles are determined by Latin Hypercube Sampling (LHS). After validation of the kriging model, it is used in conjunction with the simulated annealing and thus a meta-algorithm is developed for the solution of global optimization problem for the impeller optimization. Within the desired range of parameters, it is shown that this meta-algorithm provides a robust, reliable and fast optimization method. The procedures can be used to many problems in engineering. In this study a centrifugal fan impeller is successfully optimized using this procedure.

A method is presented for redesigning a centrifugal impeller and its inlet duct. The double-discharge volute casing is a structural constraint and is maintained for its shape. The redesign effort was geared towards meeting the design volute exit pressure while reducing the power required to operate the fan. Given the high performance of the baseline impeller, the redesign adopted a high-fidelity CFD-based computational approach capable of accounting for all aerodynamic losses. The present effort utilized a numerical optimization with experiential steering techniques to redesign the fan blades, inlet duct, and shroud of the impeller. The resulting flow path modifications not only met the pressure requirement, but also reduced the fan power by 8.8% over the baseline. A refined CFD assessment of the impeller/volute coupling and the gap between the stationary duct and the rotating shroud revealed a reduction in efficiency due to the volute and the gap. The calculations verified that the new impeller matches better with the original volute. Model-fan measured data was used to validate CFD predictions and impeller design goals. The CFD results further demonstrate a Reynolds-number effect between the model- and full-scale fans.

Abstract This study aims to optimize the impeller geometry of a backward-curved blade centrifugal fan in a helicopter oil cooler to improve the aerodynamic performance of the impeller. The study consists of three main parts: aerodynamic design and parametrization of the impeller, numerical analysis of impeller performance, and multi-objective design optimization to maximize fan static pressure and total to static isentropic efficiency. In the first part, a one-dimensional impeller design was performed using quasi-experimental methods and a direct optimization method with the multi-objective genetic algorithm, and the impeller geometry was parameterized through a commercial tool. The three-dimensional flow through the impeller was solved in the second part with a commercial computational fluid dynamics tool. The Reynolds-averaged Navier-Stokes equations were solved on a multi-block grid, and a second-order accurate finite volume method is employed. The most appropriate turbulence model and grid size were selected considering time, cost, and fidelity. In the third part, a sensitivity analysis was performed with the design-of-experiment method, and the parameters that affect the objective function most significantly were determined. A multi-objective design optimization based on a non-dominated sorting genetic algorithm was performed with the Kriging response surface method, and Pareto-optimal solutions were obtained. Results show that, at the design point, there is a 9.6% and 0.96% increase in the fan static pressure and total to static isentropic efficiency, respectively. Trained kriging response surface model predicted the fan static pressure and total to static isentropic efficiency with an error of 0.12% and 0.33%, respectively.

An optimization strategy called response surface methodology (RSM) is applied to a centrifugal fan impeller optimization design in this paper. RSM is used to generate an approximated model of objective function, for which a second-order polynomial function is chosen. The Design of experiment (DOE) technique coupled with CFD analysis is then ran to generate the database. The least-squares regression method (LS) is used to determine the coefficient of the RSM function. Finally, the Genetic Algorithms (GA) is applied to the objective function in order to obtain the optimal configuration. This paper also presents a solution to the problem of imprecise fitting of second-order RSM model by dividing the zone into several subzones which is proved to be effective in this paper. The optimization result shows that RSM is an effective and feasible optimization strategy for the centrifugal fan impeller design, and the complexity of the objective function and the overall optimization time could be significantly reduced.

Because of the complexity of internal flow characteristics of centrifugal fan, a set of wholly mature design methods of impeller theory do not exist at the present time. The paper tries to investigate and analyze the internal relations between a large number of existing aerodynamic sketches and performance parameters of centrifugal fans by means of statistical method and finds regularity. The counted and researched results show that the correspongding relations exist not only between specific speed and specific diameter but also between exit width of blade and specific speed. Based on the analysis on the selecting methods and rules of impeller's main geometric parameters of high performance centrifugal fans, the paper improved the traditional design theory of fan and proposed some new methods, which are used to determine the main geometric parameters of centrifugal fan's impeller.

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For a centrifugal fan impeller the blade shape can be defined using two parameters: the blade angle and the blade width. There are different design methods depending on the assumption made on both the blade width and the blade angle. In this paper four design methods are presented: constant blade width and variable blade angle; hyperbolic blade width and variable blade angle; hyperbolic blade width and constant blade angle; linear blade width and variable blade angle. The sequential algorithm for solving the characteristic system of equations, which defines the blade geometry, is implemented in a MATLAB script file, for which principal code lines are explained. In the solving process of the characteristic system of equations for all four design methods considered, different relationships for relative velocity are obtained. The comparative graphical analysis of impeller blades obtained by all of the four design methods, as well as the blade geometry parameters is presented.

Numerical simulation of the flow field was carried out for a whole centrifugal fan to consider the interaction of three parts—inlet, impeller, and scroll. A modern optimum design method for a centrifugal fan has been presented using a computational fluid dynamics (CFD) technique to replace the conventional method. A sample fan based on the optimum design was manufactured and tested. The numerical prediction agrees well with the test data. The excellent performance of the sample fan has proved the validity of the method adopted. Moreover, the effects of the blade inlet angle and the gap between impeller and inlet on the fan performance are quantitatively analyzed. Particularly the energy loss in every passage, including the gap loss and the leakage flow rate in the gap, are discussed in detail in the paper. It is found that the blade inlet angle and the impeller gap play an important role for fan performance.

The effect of a gap between an inlet duct and a rotating impeller in a centrifugal fan is often neglected in the impeller design calculations or design-related computational fluid dynamics (CFD) analyses. This leads to an arbitrary determination of the gap size for the final fan configuration. Since the gap guides the volute flow back to the impeller flow field near the shroud high-curvature turning area, the low-momentum jet formed by the gap flow could prevent local flow from separation, reducing the local flow turning losses. However, this jet flow has enlarged flow separation in the blade passage, producing shedding vorticity in the downstream passage-flow. The passage-flow separation and the downstream volute flow, which is also affected by the passage-flow separation, have a higher impact on flow losses than the blade leading edge separation. If the gap size is not selected carefully, the combined effect of the passage-flow separation and downstream volute flow losses reduces the fan’s overall performance between 2% points and 5% points as demonstrated in the current study. In this paper, local impeller velocity distributions obtained from both design-CFD and analysis-CFD calculations are compared along the shroud from the gap to the blade trailing edge. The overall impeller flow fields with and without the gap and volute effects are also compared and discussed based on the CFD solutions. Finally, an example of controlling the gap effect is shown.

Analytical and experimental procedures for determining the detailed internal flow behavior in the impeller of a centrifugal fan are presented. Predicted and measured values of both the detailed flow fields and overall performance of the impeller are shown to be in good agreement. The analytical procedures are based on a finite element method to predict the inviscid flow field, coupled to a semi-empirical determination of pressure losses in the impeller based on boundary layer calculations. The experimental work used to validate these predictions uses extensive surface pressure taps in the rotating impeller as well as information from inlet and discharge velocity traverses to determine overall performance. The purpose of this work is the development of accurate and reliable analytical tools for the design of air and gas moving equipment with improved performance and efficiency for the power utility market and heavy industrial applications.

The aim of this study is to evaluate the influence of design parameters on the unsteady flow in a forward-curved centrifugal fan and their impact on the aeroacoustic behavior. To do so, numerical and experimental studies have been carried out on four centrifugal impellers designed with various geometrical parameters. The same volute casing has been used to study these impellers. The effects on the unsteady flow behavior related to irregular blade spacing, blade count and radial distance between the impeller periphery and the volute tongue have been studied. The numerical simulations of the unsteady flow have been carried out using computational fluid dynamics (CFD) tools based on the unsteady Reynolds averaged Navier Stokes (URANS) approach. The study is focused on the unsteadiness induced by the aerodynamic interaction between the volute and the rotating impeller blades. In order to predict the acoustic pressure at far field, the unsteady flow variables provided by the CFD calculations have been used as inputs in the Ffowcs Williams-Hawkings equations (FW-H). The experimental part of this work concerns measurement of aerodynamic performance of the fans using a test bench built according to ISO 5801 (1997) standard. In addition to this, pressure microphones have been flush mounted on the volute tongue surface in order to measure the wall pressure fluctuations. The sound pressure level (SPL) measurements have been carried out in an anechoic room in order to remove undesired noise reflections. Finally, the numerical results have been compared with the experimental measurements and a correlation between the wall pressure fluctuations and the far field noise signals has been found.

In a conventional one-dimensional scheme design of centrifugal fans and compressors, it is assumed that there is no flow prewhirl at the impeller inlet when the inlet guide vane is absent. However, many experiments have proved that the flow prewhirl does exist at the inlet of centrifugal impellers. This results in an error in the design of centrifugal fans and compressors. In this study a new method is presented to calculate the Euler work of centrifugal impellers considering the presence of an inlet flow prewhirl in the case without the inlet guide vane. Stodola's approach dealing with the slip velocity at the impeller outlet is applied to the impeller inlet. A new formula for Euler work calculation is deduced to evaluate the effect of the inlet prewhirl. The new formula has been applied to 33 industrial centrifugal fans and the calculated results have been compared with the experimental data of these fans. The comparison shows that the new formula is more accurate in most cases than the original formula without consideration of the inlet flow prewhirl, and the accuracy has been improved by more than 10 per cent on average. The aim of this study is to improve the accuracy of the one-dimensional scheme design of centrifugal fans and to provide a reference for a similar research.

For the past two years, Mechanical & Aerospace Engineering students at the University of Florida have been designing and manufacturing impellers for a centrifugal fan. The method is taught in our Thermo-Fluids Lab and Design class and involves using Euler's Turbomachine Equation and creating velocity diagrams to predict performance. A limitation of the Euler Turbomachine Equation is that it is based on a finite control volume analysis which prescribes blade angles at the entrance and exit of the impeller, but provides no information on the number or geometry of the blades within the impeller. Another limitation of the equation is that it assumes an infinite number of blades of zero thickness that results in uniform flow at the inlet and the exit, while a real impeller has a distinct velocity profile in between each blade that leads to losses not predicted by the equation. A Digital Design Process has evolved whereby students create an initial design using the Euler method, and then create a digital model using Solidworks, and then follow that up with a computational fluid dynamics (CFD) to optimize their design. After optimization, the students manufacture a prototype of their impeller using a 3-D printer, and then test the impeller in the lab fan performance apparatus. The results of their efforts as well as the issues involved in managing such a project with about 125 students per semester will be discussed in this paper.

Performance of centrifugal fans with unshrouded impellers strongly depends upon complex configuration of the asymmetrical flowfield in the axial direction, which is highly unsteady. The flowfield, in turn, is considerably affected by the design parameters of both scroll and impeller geometry, for which tip clearance is of particular interest. This article presents a three-dimensional computational fluid dynamics (CFD) simulation of the flowfield in three different unshrouded centrifugal fan impellers with varying tip clearances. A commercial CFD code, namely, Fluent V6.2.16 with a k-ɛ two-equation turbulence model was utilized in order to study the effects of tip clearance on the overall performance of each fan with the tip clearances ranging from 5 to 30 mm. The numerical results were compared with the experimental data reported previously in the literature by the present author and his colleagues, and excellent agreements were observed for each fan.

The multi-blade centrifugal fan is small in size, compact in structure, which has high pressure coefficient and flow coefficient, but usually has low efficiency. In order to improve the aerodynamic performance of multi-blade centrifugal fan. CFD (Computational Fluid Dynamics) method was used to simulate the flow field of the fan, and the key factors affecting the performance of the fan were analyzed. According to the controllable deceleration method, a new blade profile is designed, two airfoils are used to optimize the blade shape, and the results are compared and analyzed. The results show that the newly designed profile can improve the performance of the fan, and the appropriate airfoil blade can reduce the flow loss caused by the change of Angle of attack, improve the efficiency of the fan, and make the efficiency zone wider.

Abstract A quick method for the design of efficiency-optimal centrifugal fan impellers is presented. It is based on an evolutionary optimization algorithm that identifies the optimal geometrical parameters for a given aerodynamic objective function. The range of the geometrical parameters considered allows covering aerodynamic design points appropriate for the complete class of centrifugal fans. The quickness of the method stems from evaluating the objective function using metamodels. In total, four metamodels, based on local model networks (LMN) and multi-layer perceptrons (MLP), were trained and eventually aggregated to reduce the variance (stochastic) error. The training data consist of approximately 4000 characteristic curves obtained from automated numerical steady-state Reynolds-averaged Navier–Stokes (RANS) flow simulations. The computational domain as well as the number of grid nodes and their distribution in the domain were optimized in a pre-study. For verification, a grid independence study was carried out. In addition, two criteria were defined to detect aerodynamic operating points associated with non-physical performance predictions. Finally, validation was secured with experimental data from three exemplary impeller designs. The proposed optimization scheme requires a costly initial one-time computational fluid dynamics (CFD) effort, but then allows a quick design of centrifugal fan impellers for arbitrary design points. The search for an optimal centrifugal impeller requires less than 1 min on a standard personal computer, while allowing up to 105 objective function evaluations for one search. Moreover, predicted performance curves that always come along with each design were found to be very reliable in comparison with experiments.

Abstract In order to better understand the behavior of the fluid flow in vaned centrifugal fans, theoretical and experimental work has been carried out on unsteady three-dimensional (3D) flows. Particular attention is given to the flows located at the rotor–stator interface. This zone is the seat of strong interactions between the moving part and the fixed part. This phenomenon has as consequences: Strongly unsteady flow, fluctuating forces on the stator blades, and an efficiency decrease. This work is part of a project which main objective is the aeroacoustic optimization of high speed centrifugal fans. We present in this paper the first results, mainly aerodynamic ones, which will be used thereafter as an input data to aeroacoustic modeling. A numerical simulation tool was used in order to determine the kinematics and the dynamics of these flows. The measurements of the steady and unsteady flow characteristics allowed a comparison of the theoretical and experimental results.

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Based on an analysis of design and model in the aerofoil blade, carrying out second development by using the Solidworks and Visual Basic 6.0, a digital design method of geometric model for the impeller of aerofoil blades is provided by the silhouettes of the blade section zoomed which are gained by calling functions of Solidworks API in VB program, according to the existing silhouettes of the standard aerofoil blade section. Taking impellers of the G4-68 serial centrifugal fans as applying objects, the superiority in application of VB and Solidworks is embodied on the geometric model of aerofoil blade for impellers.

The aerodynamics of transonic fans is discussed with emphasis on the use of three-dimensional design techniques, such as blade sweep and lean, to improve their performance. In order to study the interaction of these 3D features with the shock pattern a series of five different designs is produced and analysed by CFD. It is found that the 3D features have remarkably little effect on the shock pattern near the tip where the shock must remain perpendicular to the casing. Lower down the blade significant shock sweep, and hence reduced shock loss, can be induced by 3D design but this is usually at the expense of reduced stall margin and increased loss elsewhere along the blade span. Overall, very little change in peak efficiency or pressure ratio is produced by blade sweep or lean. However, there are significant effects on stall margin with forwards sweep producing a better stall margin and maintaining a high efficiency over a wider range.

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Turbomachinery active subspace performance maps are two-dimensional (2D) contour plots that illustrate the variation of key flow performance metrics with different blade designs. While such maps are easy to construct for design parameterizations with two variables, in this paper, maps will be generated for a fan blade with twenty-five design variables. Turbomachinery active subspace performance maps combine active subspaces—a new set of ideas for dimension reduction—with fundamental turbomachinery aerodynamics and design spaces. In this paper, contours of (i) cruise efficiency, (ii) cruise pressure ratio (PR), (iii) maximum climb flow capacity, and (iv) sensitivity to manufacturing variations are plotted as objectives for the fan. These maps are then used to infer pedigree design rules: how best to increase fan efficiency; how best to desensitize blade aerodynamics to the impact of manufacturing variations? In the present study, the former required both a reduction in PR and flow capacity—leading to a reduction of the strength of the leading edge bow wave—while the latter required strictly a reduction in flow capacity. While such pedigree rules can be obtained from first principles, in this paper, these rules are derived from the active subspaces. This facilitates a more detailed quantification of the aerodynamic trade-offs. Thus, instead of simply stating that a particular design is more sensitive to manufacturing variations; or that it lies on a hypothetical “efficiency cliff,” this paper seeks to visualize, quantify, and make precise such notions of turbomachinery design.

No abstract

A low pressure axial fan with swept blades is optimized with respect to sound emission and efficiency. Noise is addressed by a modified sweep strategy. Regarding aerodynamics, geometrical parameters describing variations of the blade section and the hub contour are defined. The optimum in terms of maximal total-to-total fan efficiency at the design point is achieved by numerous CFD simulations embedded in the Simplex optimization method. Besides a moderate increase in efficiency at the design point, a remarkable extension of operating range is observed. The numerical results are successfully validated against experiment measurements. Acoustic measurements furthermore show a decrease in sound emission over the complete operating range.

The aerodynamics of transonic fans is discussed with emphasis on the use of threedimensional design techniques, such as blade sweep and lean, to improve their performance. In order to study the interaction of these 3D features with the shock pattern a series of five different designs is produced and analysed by CFD. It is found that the 3D features have remarkably little effect on the shock pattern near the tip where the shock must remain perpendicular to the casing. Lower down the blade significant shock sweep, and hence reduced shock loss, can be induced by 3D design but this is usually at the expense of reduced stall margin and increased loss elsewhere along the blade span. Overall, very little change in efficiency is produced by blade sweep or lean. However, forwards lean of the rotor does produce a small increase in mass flow. Radial migration of the boundary fluid on the suction surface behind the shock is shown to play a large part in the aerodynamics near the blade tip.

An experimental and numerical investigation of detailed tip clearance flow structures and their effects on the aerodynamic performance of a modern low-aspect-ratio, high-throughflow, axial transonic fan is presented. Rotor flow fields were investigated at two clearance levels experimentally, at tip clearance to tip blade chord ratios of 0.27 and 1.87 percent, and at four clearance levels numerically, at ratios of zero, 0.27, 1.0, and 1.87 percent. The numerical method seems to calculate the rotor aerodynamics well, with some disagreement in loss calculation, which might be improved with improved turbulence modeling and a further refined grid. Both the experimental and the numerical results indicate that the performance of this class of rotors is dominated by the tip clearance flows. Rotor efficiency drops six points when the tip clearance is increased from 0.27 to 1.87 percent, and flow range decreases about 30 percent. No optimum clearance size for the present rotor was indicated. Most of the efficiency change occurs near the tip section, with the interaction between the tip clearance flow and the passage shock becoming much stronger when the tip clearance is increased. In all cases, the shock structure was three dimensional and swept, with the shock becoming normal to the endwall near the shroud.

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Comparative studies have been carried out on two axial flow fan rotors of controlled vortex design (CVD), at their design flowrate, in order to investigate the effects of circumferential forward skew on blade aerodynamics. The studies were based on computational fluid dynamics (CFD), validated on the basis of global performance and hot wire flow field measurements. The computations indicated that the forward-skewed blade tip modifies the rotor inlet condition along the entire span, due to its protrusion to the relative inlet flow field. This leads to the rearrangement of spanwise blade load distribution, increase of losses along the dominant part of span, and converts the prescribed spanwise blade circulation distribution towards a free vortex flow pattern. Due to the above, reduction in both total pressure rise and efficiency was established. By moderation of the radial outward flow on the suction side, being especially significant for non-free vortex blading, forward sweep was found to be particularly useful for potential reduction of near-tip loss in CVD rotors. Application of reliable CFD-based design systems was recommended for systematic consideration and control of both load- and loss-modifying effects due to non-radial blade stacking.

It is well known that to increase rotational velocity is one of the effective measures to increase total pressure ratio. With increasing velocity, under the condition of transonic flow, the obvious effect of maximum camber location on aerodynamics performance of compressor blades especially in the supersonics zone can be found. In order to reduce the blade losses and to improve the blade design methodology it is necessary to study this complex flow mechanism. This paper describes only the influence of relative maximum camber location on aerodynamics performance, mainly adiabatic efficiency. As an example an axial fan was designed and calculated by the methodologies developed at the Institute of Engineering Thermophysics, Chinese Academy of Sciences.

&lt;div class="htmlview paragraph"&gt;Cutting down fan system development costs, improving quality, and increasing fan efficiency is a challenge that is now being addressed by the engine cooling engineers. In order to attain such a compelling goal, a &lt;i&gt;Virtual Prototyping&lt;/i&gt; approach has been adopted, mainly based on Computational Fluid Dynamics (CFD)[&lt;span class="xref"&gt;7&lt;/span&gt;].&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;For the development of the fans used in the engine cooling systems, CFD now plays a key role as a design tool as well as an optimization tool. Until recently, both complex geometries and low-speed aerodynamics inherent to latter systems have prevented numerical simulations to be part of the design or reblading processes. Since the advent of general purpose CFD softwares capable of adressing the issues pertinent to the engine cooling system fans, a CFD based development of a new standard fan range was initiated. This paper presents the CFD strategy adopted and the results obtained on the new fans.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;Both development and re-blading of fan systems have been addressed, leading to more compact and efficient fans. Re-blading an existing fan led to a fan with 80% hydraulic efficiency. A new large diameter fan has been designed exhibiting similar performances. Comparisons between numerical results and experimental data exhibited good qualitative agreement, emphasizing the key role of CFD as a reliable tool in the design process.&lt;/div&gt;

Abstract Axial fans with a small hub-to-tip diameter ratio are used in many branches of industry. Optimization of their aerodynamic performance is important, for which using sweep, dihedral, and skew of the blades' stacking line form an important method. Investigations on axial fans with medium to high hub-to-tip diameter ratio have shown that forward sweep of blades can give an improved aerodynamic performance, especially the total-to-total efficiency. However, only a few studies for fans with a small hub-to-tip diameter ratio have been reported. For such fans, extensive regions of backflow are present behind the fan near the hub. Based on a validated computational fluid dynamics simulation method, the effects of a sweep, dihedral and skew in axial and circumferential directions (in forward and backward direction) on the aerodynamic performance of small hub-to-tip ratio fans are investigated, with a linear stacking line. Current results show that forward sweep and circumferential skew are beneficial for higher total-to-total efficiency and that higher total-to-static efficiency can be obtained by forward dihedral and axial skew. The backward shape variety generally gives negative aerodynamic effects. Forward sweep and circumferential skew shorten the radial migration path, but more flow separation is present near the hub. With forward dihedral and axial skew, the backflow region is reduced in size and axial extent, but a more significant hub corner stall region is found. The pressure reduction due to sweep and dihedral is more limited than what could be expected from wing aerodynamics.

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This paper describes the investigations performed to better understand unsteady effect that develop in a contra-rotating axial fan. More specifically, this study focuses on rotor-rotor interactions effects on unsteady characteristic and blade aerodynamic force. The investigation method is based on three-dimensional URANS simulations, in conjunction with SST turbulence model. At first, the experimental measurements are compared to evaluate ability of the numerical method in estimation of unsteady flows. The results show that rotor-rotor interaction in the contra-rotating fan played an important role in aerodynamic efficiency. Unsteady effect increased flow losses of rotor 1, but effectively inhibited flow losses of rotor 2. The inhibition effect was mainly caused by wake recovery effect of upstream wakes in the flow passage of rotor 2. Meanwhile, negative jet flow enhanced boundary layer energy of the blade of rotor 2, so that flow separation was postponed. Different configurations consider five sets of axial spacing dimensions. Specific survey of flows under the same operation conditions indicates that axial spacing is responsible for the unsteady interaction effect. The blade aerodynamics analysis shows that the influence of the downstream potential flow disturbance on rotor 1 is greater than the effect of the upstream wake on rotor 2.

Due to the fact that legal and market requirements are becoming stricter, fan noise reduction, in addition to energy efficiency, represent a challenge for fan product designers. Most experimental studies are associated with trial-and-error approaches. Therefore, numerical methods are mostly preferable. However, the quantitative prediction of the noise emitted by radial fans via numerical simulations remains challenging. The Lattice Boltzmann method (LBM) is a relatively new approach that promises a direct calculation of the aerodynamics coupled with the aeroacoustics. This article presents an LBM simulation of a centrifugal fan using the commercial Lattice Boltzmann Code SIMULIA PowerFLOW of Dassault Systèmes. The simulation model includes both the fan impeller and the spiral housing. In accordance with the experimental setup, the fan was mounted in a test bench to analyze four different operating points. The results of the LBM simulation were validated by experimental measurements. Flow information in terms of pressure rise and efficiency of the centrifugal fan as a function of the flow rate are in a good agreement. Considering the acoustic spectra and the blade passing frequency, the simulation was able to precisely predict the noise of the centrifugal fan. The simulation results are also used to visualize the flow and acoustic field inside of the fan to detect noise-generating flow features. By evaluating the filtered pressure fluctuation in the fluid volume and on the wall, four main noise sources of the centrifugal fan can be identified.

The fan component which was designed for the energy efficient engine is an advanced high performance, single stage system and is based on technology advancements in aerodynamics and structure mechanics. Two fan components were designed, both meeting the integrated core/low spool engine efficiency goal of 84.5%. The primary configuration, envisioned for a future flight propulsion system, features a shroudless, hollow blade and offers a predicted efficiency of 87.3%. A more conventional blade was designed, as a back up, for the integrated core/low spool demonstrator engine. The alternate blade configuration has a predicted efficiency of 86.3% for the future flight propulsion system. Both fan configurations meet goals established for efficiency surge margin, structural integrity and durability.

Integrating a fan with a boundary layer ingestion (BLI) configuration into an aircraft fuselage can improve propulsion efficiency by utilizing the lower momentum airflow in the boundary layer developed due to the surface drag of the fuselage. As a consequence, velocity and total pressure variations distort the flow field entering the fan in both the circumferential and radial directions. Such variations can negatively affect fan aerodynamics and give rise to vibration issues. A fan configuration to benefit from BLI needs to allow for distortion without large penalties. Full annulus unsteady computational fluid dynamics (CFD) with all blades and vanes is used to evaluate the effects on aerodynamic loading and forcing on a fan designed to be mounted on an adapted rear fuselage of a Fokker 100 aircraft, i.e., a tail cone thruster. The distortion pattern used as a boundary condition on the fan is taken from a CFD analysis of the whole aircraft with a simplified model of the installed fan. Detailed simulations of the fan are conducted to better understand the relation between ingested distortion and the harmonic forcing. The results suggest that the normalized harmonic forcing spectrum is primarily correlated to the circumferential variation of inlet total pressure. In this study, the evaluated harmonic forces correlate with the total pressure variation at the inlet for the first 12 engine orders, with some exceptions where the response is very low. At higher harmonics, the distortion content as well as the response become very low, with amplitudes in the order of magnitude lower than the principal disturbances. The change in harmonic forcing resulting from raising the working line, thus, increasing the incidence on the fan rotor, increases the forcing moderately. The distortion transfers through the fan resulting in a non-axisymmetric aerodynamic loading of the outlet guide vane (OGV) that has a clear effect on the aerodynamics. The time average aerodynamic load and also the harmonic forcing of the OGV vary strongly around the circumference. In particular, this is the case for some of the vanes at higher back pressure, most likely due to an interaction with separations starting to occur on vanes operating in unfavorable conditions.

An experimental investigation of the aerodynamic performance and noise emission of airfoils and fan blades with perforated leading edges is presented. In a first step, a detailed wind tunnel study was carried out. Therefore, measurements on sixteen airfoils with different leading edge designs were performed for various flow speeds and geometric angles of attack. The airfoils with perforated leading edges were made of an aluminum alloy using a powder bed fusion based additive manufacturing process. For the measurements, two turbulence grids were used to generate different inflow turbulence conditions. The aerodynamic performance was captured with a wind tunnel balance and the acoustic measurements were performed using a planar microphone array. Based on the results from that study, unskewed fan blades with four different perforated leading edge designs were manufactured in a second step. With the aim of reducing turbulence ingestion noise of axial fans, the axial fans were examined with regard to their aerodynamics, total-to-static efficiency and sound emissions under free inflow and grid-generated turbulent inflow conditions. The investigations on airfoils and fan blades with perforated leading edge show a notable frequency-dependent noise reduction, but also a loss of aerodynamic performance.

During engine operation, fan casing abradable liners are worn by the blade tip, resulting in the formation of trenches. This paper describes the influence of these trenches on the fan blade tip aerodynamics. A detailed understanding of the fan tip flow features for cropped and trenched clearances is first developed. A parametric model is then used to model trenches in the casing above the blade tip and varying blade tip positions. It is shown that increasing clearance via a trench reduces performance by less than increasing clearance through cropping the blade tip. A response surface method is then used to generate a model that can predict fan efficiency for a given set of clearance and trench parameters. This model can be used to influence fan blade design and understand engine performance degradation in service. It is shown that an efficiency benefit can be achieved by increasing the amount of tip rubbing, leading to a greater portion of the tip clearance sat within the trench. It is shown that the efficiency sensitivity to clearance is biased toward the leading edge (LE) for cropped tips and the trailing edge (TE) for trenches.

Future civil transport designs may incorporate engine inlets integrated into the body of the aircraft to take advantage of efficiency increases due to weight and drag reduction. Additional increases in engine efficiency are predicted if the inlet ingests the lower momentum boundary layer flow. Previous studies have shown, however, that efficiency benefits of Boundary Layer Ingesting (BLI) ingestion are very sensitive to the magnitude of fan and duct losses, and blade structural response to the non-uniform flow field that results from a BLI inlet has not been studied in-depth. This paper presents an effort to extend the modeling capabilities of an existing rotating turbomachinery unsteady analysis code to include the ability to solve the external and internal flow fields of a BLI inlet. The TURBO code has been a successful tool in evaluating fan response to flow distortions for traditional engine/inlet integrations, such as the development of rotating stall and inlet distortion through compressor stages. This paper describes the first phase of an effort to extend the TURBO model to calculate the external and inlet flowfield upstream of fan so that accurate pressure distortions that result from BLI configurations can be computed and used to analyze fan aerodynamics and structural response. To validate the TURBO program modifications for the BLI flowfield, experimental test data obtained by NASA for a flushmounted S-duct with large amounts of boundary layer ingestion was modeled. Results for the flow upstream and in the inlet are presented and compared to experimental data for several high Reynolds number flows to validate the modifications to the solver. Quantitative data is presented that indicates good predictive capability of the model in the upstream flow. A representative fan is attached to the inlet and results are presented for the coupled inlet/fan model. The impact on the total pressure distortion at the AIP after the fan is attached is examined.\n\n

This paper presents the optimization design of a high bypass ratio civil fan blade with the consideration of aerodynamics, static and dynamic mechanics. The baseline fan blade was designed with a conventional approach without using automatic optimization techniques on both the aero side and the mechanical side. Therefore, the objective of this paper is to achieve a higher aero-mechanical performance under the multiple aerodynamic and mechanical constraints. Before the optimization, the static stress and modal analysis are performed on the baseline fan blade with/without the introduction of the arc dovetail root and shank. The results are compared to investigate the necessity of including the arc root and shank in the aero-mechanical optimization. With respect to the optimization process, the numerical design of experiment (DOE) by means of high fidelity CFD/FEA computations is firstly performed to construct the database for the initialization of Kriging surrogate mode. After that, the surrogate model is integrated with the optimization design process, and the non-dominated sorting genetic algorithm (NSGAII) is implemented to obtain the Pareto front, based on which the optimal design is selected. Utilizing this optimization process, both the aero-only and aero-mechanical optimizations are carried out. The results show that the attenuation of the 3D shock wave strength between the middle and shroud span improves the overall aero performance of the fan blade in both the aero-only optimal design and the aero-mechanical optimal design. Compared with the aero-only optimal design, the aero-mechanical optimal design shows the efficiency penalty within all the operation range simulated, however, the mechanical performance is significantly enhanced by the mitigation of the static stress level on the entire arc dovetail root and shank as well as the increase of the resonance margin.

Two blade curvatures representative of those found in automotive fans are compared. Measured performances are analyzed for forward and backward curved blades, either with or without heat-exchangers placed in front of them. The backward fan demonstrated good efficiency but poor acoustics, whereas it is the contrary for the forward fan. Investigations are completed by a numerical analysis of the flow in the cooling module. Different integration effects are highlighted depending on the blade curvature, showing variation in pressure, torque and efficiency. Analyses of blade loadings show that the flow is more homogeneous with a forward curved fan and it produces less unsteadiness at the blade tip. Post-processing of detached eddy simulations (DES) shows density fluctuations on the blade wall and confirms the correlation between the large vortical structures and the acoustic sources for both fans. In addition, with the forward fan, the sound propagation is less directed towards the axis of rotation and it yields up to −3.6 dB of sound pressure level (SPL) measured in front of the cooling module. As a conclusion, any choice for a fan must result from a compromise between aerodynamics and aeroacoustics, and the final performances must be carefully checked on the module.

A fan blade is a complicated object and obviously it is subjected to geometrical uncertainties from manufacture tolerances and other production deviations. In spite of all uncertainties a fan blade should provide stable aerodynamic efficiency and strength properties. That is why it is considered to solve a multidimensional and multidisciplinary optimization task (aerodynamics, strength and flutter sensitivity) in robust statement under geometrical uncertainties. In the proposed test case geometrical uncertainties from the fan blade manufacture tolerances and deviations are considered. The probability density function (pdf) was obtained as a result of statistical operation upon the results of blade coordinate measurements. Approximately 2500 fan blades were measured by means of CMM process to reconstruct the pdf for more than 40 geometrical uncertainties (there are blade thicknesses for different airfoil locations in several cross-sections). CFD and FEM calculations were carried out in NUMECA FINE/Turbo and ANSYS software, correspondingly. The surrogate model technique (the response surface and the Monte-Carlo method implemented to RSM results) was applied for the uncertainty quantification and the robust optimization process for the task under consideration. APPROX software was used for surrogate model construction. The IOSO technology was employed as one of the robust optimization tools. This technology is also based on a widespread application of the response surface technique. As a result, robust optimal solutions (the Pareto set) for all 4 considered criteria (aerodynamic efficiency, structural properties, stall margin and flutter sensitivity) were obtained. The probabilistic criteria were assessed based on the results obtained. The robust optimization results were compared with the deterministic optimization results.

Degradation of compressors is a common concern for operators of gas turbine engines (GTEs). Surface roughness, due to erosion or fouling, is considered one of the major factors of the degradation phenomenon in compressors that can negatively affect the designed pressure rise, efficiency, and, therefore, the engine aero/thermodynamic performance. The understanding of the aerodynamic implications of varying the blade surface roughness plays a significant role in establishing the magnitude of performance degradation. The present work investigates the implications due to the degradation of the compressor caused by the operation in eroding environments on the gas turbine cycle performance linking, thereby, the compressor aerodynamics with a thermodynamic cycle. At the core of the present study is the numerical assessment of the effect of surface roughness on compressor performance employing the Computational Fluid Dynamics (CFD) tools. The research engine test case employed in the study comprised a fan, bypass, and two stages of the low pressure compressor (booster). Three operating conditions on the 100% speed-line, including the design point, were investigated. Five roughness cases, in addition to the smooth case, with equivalent sand-grain roughness (ks) of 15, 30, 45, 60, and 150 µm were simulated. Turbomatch the Cranfield in-house gas turbine performance simulation software, was employed to model the degraded engine performance. The study showed that the increase in the uniform roughness is associated with sizable drops in efficiency, booster pressure ratio (PR), non-dimensional mass flow (NDMF), and overall engine pressure ratio (EPR) together with rises in turbine entry temperature (TET) and specific fuel consumption (SFC). The performance degradation evaluation employed variables such as isentropic efficiency (ηis), low pressure compressor (LPC) PR, NDMF, TET, SFC, andEPR. The variation in these quantities showed, for the maximum blade surface degradation case, drops of 7.68%, 2.62% and 3.53%, rises of 1.14% and 0.69%, and a drop of 0.86%, respectively.

An experimental investigation on the aerodynamic performances of thick blades axial-flow fans was carried out in this study. Two fans are considered, the first one is rotomoulded (in plastic) and the second one is milled (in aluminium). Both have exactly the same shape, except that the rotomoulded fan has hollow blades. They were designed from an existing fan (manufactured by plastic injection process) used in the cooling system of an automotive vehicle power unit. As far as shape is concerned, the only difference between the two first fans and the traditional injected fan is the blade thickness, whereas as far as rigidity is concerned, the only difference between the rotomoulded and the milled fans is the ability of the rotomoulded fan to be deformed easier than the milled fan. The aim of this study is to determine on the one hand the influence of the blade thickness and on the other hand the way the deformation of the hollow blades may affect the global and the local performances. The global performances of the fans were measured in a test bench designed according to the ISO 5801 standards. The curve of the aerodynamics characteristics (pressure head versus flow rate) and of the global efficiency are slightly lower for the roto-moulded fan. The wall pressure fluctuations were also investigated for three flow rates: one corresponding to the maximum efficiencies of both fans and the two others corresponding to an under-flow and an over-flow rate. The power spectral density (PSD) levels, are between six and nine times higher for the roto-moulded fan at nominal flow rate. At partial flow rate, however, the PSD levels are close for both fans.

The advancements in fan technology are nowadays animated by two major drivers: the legal requirements that impose minimum fan efficiency grades for fans sold within European Union (and soon US and Asia), and the market request for better air performance and lower sound emissions. Within HVAC (Heating, Ventilating and Air Conditioning) applications, centrifugal fans with forward curved blades are widely used due to the higher total pressure rise capability and lower acoustic emissions with respect to more efficient backward curved blades. However the continuous rise of minimum fan efficiency grades pushes the manufacturers to develop a new generation of forward curved centrifugal fans, improving previous design. Here the challenge is not only on aerodynamics, but in the overall production process, as squirrel cage fans are characterised by a cost-effective consolidated technology, based on simple blade geometries and easy series manufacturing. For example, the blades usually have circular camber lines, as results of cut cylinders. Thus, once the number of blades and the angle at the leading edge are selected, the chord and the deflection capability are constrained as well. These concurring aspects led industry to include in the design process new tools, in particular CFD, to analyse the flow features of the current generation of fans in order to understand which phenomena are to be either controlled or exploited to increase efficiency and total pressure rise. Here we present a numerical investigation on a forward curved blade centrifugal fan for HVAC applications, to highlight the flow features inside the impeller and in the critical region of coupling with the volute. The analysis was carried out with OpenFOAM, an open-source library for CFD. Computations were performed with the frozen rotor approach and validated against available experimental data.

The Onera elsA CFD software is both a software package capitalizing the innovative results of research over time and a multi-purpose tool for applied CFD and multi-physics. The research input from Onera and other laboratories and the feedback from aeronautical industry users allow enhancement of its capabilities and continuous improvement. The paper presents recent accomplishments of varying complexity from research and industry for a wide range of aerospace applications: aircraft, helicopters, turbomachinery...

In recent years, unmanned aerial vehicles (UAVs) have been developed and studied for various applications, including drone deliveries, broadcasting, scouting, crop dusting, and firefighting. To enable the wide use of UAVs, their exact aeroacoustic characteristics must be assessed. In this study, a noise prediction method for a ducted fan UAV with complicated geometry was developed. In general, calculation efficiency is increased by simulating a ducted fan UAV without the struts that fix the fuselage to the ducts. However, numerical predictions of noise and aerodynamics differ according to whether struts are present. In terms of aerodynamic performance, the total thrust with and without struts is similar owing to the tendency of the thrust of a blade to offset the drag of the struts. However, in aeroacoustic simulations, the strut effect should be considered in order to predict the UAV’s noise because noise from the blades can be changed by the strut effect. Modelling of the strut effect revealed that the dominant tonal noises were closely correlated with the blade passage frequency of the experimental results. Based on the successful detection of noise sources from a ducted fan UAV system, using the proposed noise contribution contour, methods for noise reduction can be suggested by comparing numerical results with measured noise profiles.

Achievement of an optimal compressor design with respect to its aerodynamic performance and feasible structural mechanics within an automated optimization process is subject of this paper. The compressor considered is a highly loaded, transonic fan stage, designed for achievement of a very high pressure ratio. To ensure operation in highly integrated installation conditions, a sufficient stability margin is of major concern. Multiple aerodynamic operating points at two rotational speeds allowed optimization of both the stability margin and the working line stage efficiency. On the part of structural mechanics, several static stress criteria were addressed for definite blade regions as well as the dynamic blade behavior in terms of the Campbell diagram. An optimization strategy was chosen, which targeted firstly on the fulfillment of multiple mechanical and aerodynamical constraints, while the aerodynamic performance was under constraint itself. Upon achievement, optimization aimed for maximum aerodynamic performance while keeping mechanics feasible. Response surfaces have been incorporated in the optimization process to reconcile costly high fidelity CFD and structural simulations with the large number of 114 free design parameters. Furthermore, optimization on these models enabled a successfully accomplishment of the constraint issue by a large number of numerically cheaper fitness evaluations. Starting from an already optimized baseline configuration, the current work targeted an improvement of the rotor aerodynamics in the transonic hub region and the resolution of previously unsolved problems concerning the rotor structural mechanics. Free design parameters were hub and casing contours in the rotor part, the shape of the leading and trailing blade edges and a high degree of freedom for rotor profile sections in the lower half of the blade.

Wells turbine is a kind of self-rectified air turbines used in an oscillatory water column (OWC) device for wave energy conversion. In this study, a steady three-dimensional simulation of a fan-shaped Wells turbine is performed on Star CCM+ commercial software by solving the Reynolds-averaged Navier-Stokes (RANS) equations. The turbulence effects are taken into account by using the Spalart-Allmaras turbulence model. Good agreement between the numerical results and the experimental results within the operation region (5&lt; α &lt;11 degrees) is observed. The geometry of the turbine rotor has a significant effect on the performance of energy conversion. Inspired by the aerodynamics of low Reynolds flyer, the normal fan-shaped Wells turbine is optimized by a bio-mimetic method in which the profile of a hawk moth wing of Manduca Sexta is applied on the blades. The modified turbine has a lower torque and pressure drop coefficient with higher efficiency. The maximum efficiency for the modified turbine is 0.61, compared to 0.48 for the normal fan-shaped one. By analysis of the detailed flow-field, it has also been found that only the middle parts of the blade can effectively generate the momentum. In order to acquire a higher efficiency, further optimization is carried out by refining some blade parts in the tip and the hub which cannot effectively produce power.

Uncertainties surrounding the influence of Reynolds number on the performance of air handling turbomachines are as old as the study of turbomachinery fluid dynamics. In particular, all low-speed turbomachines and most axial-flow fans feature Reynolds numbers that are often lower than the critical value, above which the literature states a limited dependency of blades cascade aerodynamics on Reynolds number. Testing standards already account for this well-known issue, which arises mainly in the case of geometrically similar fans of different size and/or operating conditions. On the other hand, one of the main practical issues in the design of low-speed machines is the disagreement among the most authoritative sources on the value of the critical Reynolds number for axial fans. The many definitions of Reynolds number, which are suited to either fan design purposes or fan performance assessment, introduce additional problems, as the corresponding values may differ by orders of magnitude depending on the chosen definition. A less debated issue deals with the effect of Reynolds number on global performance and efficiency parameters for different axial-flow fan configurations. This paper reports pressure and efficiency data measured at several rotational speeds of four axial fans that feature different configurations, hub-to-tip ratios, sizes and surface finishes. In particular, the tests consider two 315mm and one 630mm tube-axial fans, and one 800mm vane-axial fan with preswirler blading. Data on two vane-axial fans with straightener, and one preswirler-rotor-stator stage, available in the literature, widen the discussion on the Reynolds number effect on the entire category of single-stage axial fans.

The fan blade configuration affects its efficiency and sound pressure level—(SPL). This paper analyzes the fan blade noise components and studies the aerodynamic characteristics of fan blades. The bar theory and moving soundfield characteristics are used in the theoretical analysis. Nonlinear aerodynamics theory is used to analyze the blade force. A mathematical model of fan blade noise is developed and simulated by the precision Gauss-Legendre method. The model simulation and the experiment results are analyzed in the frequency domain. The simulation results are in reasonable agreement with the measured data. Our model and the Fukano model are compared for different rotational speeds of the fan. This paper then studies the change of SPL when the blade parameters (number of blades, rotation speed of fan, chord of fan, and blade profile etc.) vary. The major factors affecting the fan noise are analyzed. Our model is derived from the viewpoint of blade design, so the result can be used to study the aerodynamic characteristics of fan blades quantitatively. The study is considered as a prerequisite to designing fans of high quality, since it provides a theoretical basis for noise prediction and noise control.

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This paper presents the energy-saving effect of a single-drive bearingless motor. In the single-drive bearingless motor, only the axial direction is actively positioned. The other radial and tilting directions are passively stabilized by repulsive passive magnetic bearings. Therefore, it has the advantages of low cost, absence of contact, maintenance-free and a long lifetime. In this paper, an additional advantage, an energy-saving effect, is verified. In experiments, the input power is measured with and without mechanical ball bearings. The bearingless motor can reduce the input power because the magnetic suspension power is low compared with the mechanical bearing loss. In addition, it is found that the efficiency can be improved.

Pressure pulsations may cause high-amplitude vibrations during the process of a centrifugal pump. The trailing edge shape of the blade has a critical influence on the pump’s pressure fluctuation and hydraulic characterization. In this paper, inspired by the humpback whale flipper, the authors research the impact of applying the sinusoidal tubercles to the blade suction side of the trailing edge. Numerical calculation and experiments are carried out to investigate the impact of the trailing edge shape on the pressure pulsations and performance of a centrifugal pump with low specific speed. Two designed impellers are tested, one is a sinusoidal tubercle trailing edge (STTE) impeller and the other is the original trailing edge (OTE) prototype. The detailed study indicates that the sinusoidal tubercle trailing edge (STTE) reduces pressure pulsation and enhances hydraulic performance. In the volute tongue region, the pressure pulsation amplitudes of STTE at fBPF decrease significantly. The STTE impeller also effectively changes the vortex structure and intensity in the blade trailing edge area. This investigation will be of great benefit to the optimal design of pumps.

In a centrifugal compressor the flow around the diffuser is collected and led to the pipe system by a spiral-shaped volute. In this study a single-stage centrifugal compressor with three different volutes is investigated. The compressorwas first equipped with the original volute, the cross-section of which was a combination of a rectangle and semi-circle. Next a new volute with a fully circular cross-section was designed and manufactured. Finally, the circular volute wasmodified by rounding the tongue and smoothing the tongue area. The overall performance of the compressor as well as the static pressure distribution after the impeller and on the volute surface were measured. The flow entering the volute was measured using a three-hole Cobra-probe, and flow visualisations were carriedout in the exit cone of the volute. In addition, the radial force acting on theimpeller was measured using magnetic bearings. The complete compressor with thecircular volute (inlet pipe, full impeller, diffuser, volute and outlet pipe) was also modelled using computational fluid dynamics (CFD). A fully 3-D viscous flow was solved using a Navier-Stokes solver, Finflo, developed at Helsinki University of Technology. Chien's k-e model was used to take account of the turbulence. The differences observed in the performance of the different volutes were quite small. The biggest differences were at low speeds and high volume flows,i.e. when the flow entered the volute most radially. In this operating regime the efficiency of the compressor with the modified circular volute was about two percentage points higher than with the other volutes. Also, according to the Cobra-probe measurements and flow visualisations, the modified circular volute performed better than the other volutes in this operating area. The circumferential static pressure distribution in the volute showed increases at low flow, constant distribution at the design flow and decrease at high flow. The non-uniform static pressure distribution of the volute was transmitted backwards across the vaneless diffuser and observed at the impeller exit. At low volume flow a strong two-wave pattern developed into the static pressure distribution at the impeller exit due to the response of the impeller to the non-uniformity of pressure. The radial force of the impeller was the greatest at the choke limit, the smallest atthe design flow, and moderate at low flow. At low flow the force increase was quite mild, whereas the increase at high flow was rapid. Thus, the non-uniformityof pressure and the force related to it are strong especially at high flow. Theforce caused by the modified circular volute was weaker at choke and more symmetric as a function of the volume flow than the force caused by the other volutes.

The multi-blade centrifugal fan is commonly used in modern building ventilation and air-conditioning system. However, it does not readily satisfy the increasing demand for energy saving, high efficiency or noise reduction. Its performance is inherently limited by the geometrical structure of single circular arc blades. Q35-type multi-blade centrifugal fan studied as an example by combining the disturbance CST function to parameterize the blades. The optimization parameter change range is confirmed, and test samples are extracted before establishing an RBF proxy model. The NSGA-II algorithm is incorporated, and multi-objective optimization is performed with flow rate and total pressure efficiency as optimization goals. The results show that the fan performance is effectively improved. At the design working point, the air volume of the multi-blade centrifugal fan increases by 1.4 m3/min; at the same time, the total pressure efficiency increases by 3.1%, and the noise is reduced by 1.12 dB, applying the proposed design. The obtained higher fan efficiency can effectively improve performance of the whole ventilation and air-conditioning system. This novel optimization method also has relatively few parameters, which makes it potentially valuable for designing multi-wing centrifugal and other types of fans, providing a new idea for energy saving and emission reduction design of fan.

The origins and effects of the complex vortex structure near the volute outlet of a multi-blade centrifugal fan are investigated in this paper. Due to the wide blade and short blade channel, the airflow maintains a large radial velocity during the blade channel. This continuous radial partial velocity causes vortices to be generated at the region of volute outlet. Then, the secondary flow close to the impeller generate from the center to the sides in volute. It is obtained that the streamlines are divided into two parts (backflow and outflow) at volute outlet. Although the vortices near volute outlet region are complex, the main features of flow behavior caused by the vortex are understandable.

Adhesion systems are very important in robots for infrastructure inspection (especially in vertical walls). They present the challenge of optimizing the ratio vacuum/power consumption in battery-powered robots. In this paper, a CFD (computer fluid dynamics) modelling and optimization process of a robot adhesion system is carried out to determine the best performing configuration in terms of vacuum and power consumption. Analytical and numerical models were developed to predict the behaviour of the system for different configurations. The models were validated, using test rig measurements, by calibrating an arbitrary defined inlet height that simulates the leakage flow. Then, different geometric parameters were varied to determine the best performing configuration based on the vacuum/power consumption ratio value. The model presented in the paper was capable of predicting the behaviour of the system for different configurations, with a margin of error of 15% for the vacuum prediction and 25% for the motor power calculation. Finally, the model was used to optimize parameters of the system, like the number of blades of the impeller. The adhesion system was conceived for the modular autonomous climbing legged robot ROMERIN.

Damage caused by erosion has been reported in several industries for a wide range of situations. In the present work, a new method is presented to improve the erosion resistance of machine components by biomimetic method. A numerical investigation of solid particle erosion in the standard and biomimetic configuration blade of axial fan is presented. The analysis consists in the application of the discrete phase model, for modeling the solid particles flow, and the Eulerian conservation equations to the continuous phase. The numerical study employs computational fluid dynamics (CFD) software, based on a finite volume method. User-defined function was used to define wear equation. Gas/solid flow axial fan was simulated to calculate the erosion rate of the particles on the fan blades and comparatively analyzed the erosive wear of the smooth surface, the groove-shaped, and convex hull-shaped biomimetic surface axial flow fan blade. The results show that the groove-shaped biomimetic blade antierosion ability is better than that of the other two fan blades. Thoroughly analyze of antierosion mechanism of the biomimetic blade from many factors including the flow velocity contours and flow path lines, impact velocity, impact angle, particle trajectories, and the number of collisions.

Inspired by the low-noise characteristics of the eagle-owl nocturnal flight, two novel designs for blades of the voluteless centrifugal fan are proposed to improve the aerodynamic performance and reduce the noise. A serrated structure inspired by the eagle-owl wingtips at the trailing edge is adopted to design and optimize the blade. Based on the computational fluid dynamics methods and the Ffowcs Williams–Hawkings equation, the impact of the serrated leading and trailing edges on the aerodynamic performance and acoustic characteristics of a fan is investigated. The optimal geometric parameters of the bionic sawtooth are determined. Subsequently, a comprehensive comparison of the flow characteristics and noise spectra among the fan with the original blade (OBLE), the serrated leading-edge blade (SLBE), and the serrated trailing-edge blade (STBE) is conducted, revealing the control mechanism of the SLBE and STBE on the flow properties and noise optimization principles. Results demonstrate that the SLBE fan not only mitigates pressure fluctuations and optimizes vortices but also increases the maximum flow rate by 1.76%. Although the STBE fan also optimizes pressure and vortices, its efficiency slightly decreases due to reduced blade lift. However, the STBE fan achieves outstanding noise suppression, reducing the sound pressure level (SPL) by 6.42 dB compared to the OBLE fan. While the SLBE fan yields a limited SPL reduction of only 1.97 dB. Additionally, the noise energy shift at 1364 Hz demonstrates frequency modulation caused by the serrations. The blade trailing edge is identified as the primary noise source, and the STBE fan significantly attenuates broadband and tonal noise by optimizing the airflow disturbance suppression at the impeller outlet. These findings validate the feasibility of using biomimetic serrated designs to optimize the performance of voluteless centrifugal fans.

Taking inspiration from previous biomimetic studies on the performance of humpback whale flippers, this paper reports a programme of work to design a ‘whale-fan’ that incorporates a sinusoidal leading-edge blade profile that mimics the tubercles on humpback whales flippers. Previous researchers have used two-dimensional cascades of aerofoils to study the effects of a sinusoidal profile on aerofoil lift and drag performance. The research was primarily concerned with elucidating the fluid-flow mechanisms induced by the sinusoidal profile and the impact of those mechanisms on aerofoil performance. The results indicate that a sinusoidal leading-edge profile has improved lift recovery post-stall and, thus, is inherently more aerodynamically resistant to the effect of stall. The reported research focuses on the application of previous research conducted with infinite span cascades of aerofoils to the design and optimisation of a finite span aerofoil. The paper presents the assumptions when developing a three-dimensional aerofoil-design methodology that correlates the sinusoidal profile of the blade-leading edge with the desired vorticity distribution at the trailing edge. The authors apply the developed methodology to the design of a fan blade’s tip region to control separation at the trailing edge. The paper presents numerically derived whale-fan performance characteristics and compares them with both numerically and experimentally derived performance characteristics of the baseline fan.

Mixed flow fan is a kind of widely used turbomachine, which has faced problems of further performance improvement in traditional design methods in recent decades. Inspired by the microgrooves such as riblets and denticles on bird feathers and shark skins, we here propose biomimetic designs of various blades with the bio-inspired grooves, aiming at the improvement of the aeroacoustic performance. Based on a systematic study with computational fluid dynamic analyses, we found that these designs had the potential in noise suppression even with macroscopic grooves. Our best design can suppress turbulence kinetic energy by approximately 38% at the blade leading edge with aerodynamic efficiency loss of only 0.3 percentage points. This improvement is achieved by passive flow control. The vortical structures are changed in a favorable way at the leading edge due to the grooves. We believe that these biomimetic designs could provide a promising future of enhancing the performance of mixed flow fans by making grooves of ideal flow passages on the suction faces of blades in accord with the theory of pump design.

There is an increasing need in industry for noise reduction in fans. Inspired by owls' silent flight, we propose four owl-inspired blade designs for a mixed-flow fan to examine whether leading-edge (LE) and/or trailing-edge (TE) serrations can resolve the tradeoff between sound suppression and aerodynamic performance. We investigate the blades' aeroacoustic characteristics through various experimental methods and large-eddy simulation (LES)-based numerical analyses. Experimental results suggest that 'slotted', simply-fabricated LE serrations can achieve a lowering of the noise level while sustaining the aerodynamic performance of the fan, whereas TE serrations fail. In addition, the inclination angle can improve LE serration performance in aeroacoustic and aerodynamic performance with a reduction in the specific noise level by around 1.4 dB. LES results and noise spectral analysis indicate that the LE serrations can suppress flow separation, reducing the broadband noise at low-to-middle frequencies (40-4k Hz). This passive-flow-control mechanism, likely due to local higher incidence angles associated with LE serrations, is capable of alleviating the intensive pressure gradient while suppressing wall-pressure fluctuations over the LE region, hence weakening the Kelvin-Helmholtz instability. The tonal noise also shows a marked reduction at the highest peak frequency associated with fan-vane interaction. Moreover, we find that the high-frequency noise by-product radiates mainly from the LE serrations andsurroundings, due to the small eddies broken up when the vortical flows pass through the LE serrations. Our results demonstrate that the biomimetic design of the LE serrations can facilitate the break-up of LE vortices passively and effectively without negatively impacting aerodynamic performance, which can be utilized as an effective device to improve the aeroacoustic performance of fan blades.

We report on a numerical study on the performance of an innovative axial flow fan for large tunnel ventilation. Taking a lead from a previous biomimetic analysis on the performance of the flippers of the humpback whale, this whale-fan was designed with sinusoidal-like leading edge that mimic the tubercles of the whale. We found that this provided a resistance to stall and improved lift recovery in post-stall operations. The sinusoidal profile of the leading edge allowed to control the distribution of vorticity on the suction surface of the blades and increase the stall margin of the device. The paper discusses the design methodology that was followed to correlate the sinusoidal shape of the leading edge of the blade with the desired vorticity distribution at the trailing edge that was needed to control separation. In the paper we show the results of numerical computations carried out with the finite volume open-source code Open FOAM on the whale-fan as well as a baseline fan with straight leading edge. Reynolds Averaged Navier-Stokes equations for incompressible flow were solved with a nonlinear (cubic) eddy-viscosity k-ε model that was found able to control the eddy viscosity distribution in order to account for anisotropy of Reynolds stresses and better reproduce the three-dimensional properties of the flow field. The paper shows the performance chart of the whale-fan, derived from numerical computations, and gives an insight of the fluid flow mechanisms that are generated by the sinusoidal leading edge on the suction surface of the fan. A comparison with the baseline fan with straight leading edge is provided in order to highlight how the shape of the leading edges affect the performance of the fan. Copyright © 2013 by ASME.

Multi-blade centrifugal fans find wide application across various fields, with their internal airflow exhibiting complex turbulent behavior in three dimensions. Historically, blade optimization relied on constant thickness airfoils, limiting the effectiveness of optimization efforts. However, marine organisms have developed airfoil structures with highly efficient drag reduction, offering a novel approach to optimizing multi-blade centrifugal fans. This study proposes an airfoil optimization design method utilizing variable-thickness airfoils to maintain consistent pressure surface leading-edge parameters. By integrating the Non-dominated Sorting Genetic Algorithm II with biomimetic optimization design, performance improvements are achieved. The study constructs an asymmetric bionic blade using a Bezier curve to fit the mean camber line of the blade. Experimental testing validates the optimized fan's performance, demonstrating the effectiveness of the proposed design approach in reducing the unsteady interaction between the impeller and the volute tongue. This reduction significantly diminishes sound pressure fluctuations on the blade surface. Notably, at the maximum volume flow rate, the optimized fan featuring the asymmetric bionic blade exhibits a remarkable enhancement, with a 10.5% increase in volume flow rate and a notable 1.7 dB reduction in noise compared to the original fan configuration.

Sand erosion is a phenomenon that solid particles impinging to a wall cause serious mechanical damages to its surface. It's tough to be a machine in the desert: particles of dirt and sand work their way into moving parts, where they abrade helicopter propellers, airplane rotor blades, pipes and other equipments. However, the desert scorpion ( Androctonus australis ) live their entire lives subjected to blowing sand, yet they never appear to be eroded. In this study, the anti–erosion characteristic rules of the scorpion surfaces under aerodynamics effect of gas/solid mixed media were studied. Biomimetic linear–cutted surfaces consisting of an array of three types of grooves, square–type, V–type and U–type, were designed and investigated to quantify their erosion wear resistance properties. A smooth surface sample was fabricated for comparison. The ANSYS-Fluent simulation of biomimetic models showed that the V-type groove sample, inspired by the desert organism's surface with different morphologies, exhibited the best erosion resistance. It also indicated the anti-erosion property of biomimetic samples could be attributed to the rotating flow in the grooves that reduces the impact speed of particles. The synchronized erosion test confirmed the conclusions. Furthermore, an application exploring of bionic blades on a centrifugal fan was conducted. The blades with optimum parameters could effectively improve anti-erosion property by 29%. We envision that more opportunities for biomimetic application in improving the anti–erosion performance of parts that work under dirt and sand particle environment will be proposed.

The humpback whale (Megaptera novaeangliae) is exceptional among the large baleen whales in its ability to undertake aquabatic maneuvers to catch prey. Humpback whales utilize extremely mobile, wing-like flippers for banking and turning. Large rounded tubercles along the leading edge of the flipper are morphological structures that are unique in nature. The tubercles on the leading edge act as passive-flow control devices that improve performance and maneuverability of the flipper. Experimental analysis of finite wing models has demonstrated that the presence of tubercles produces a delay in the angle of attack until stall, thereby increasing maximum lift and decreasing drag. Possible fluid-dynamic mechanisms for improved performance include delay of stall through generation of a vortex and modification of the boundary layer, and increase in effective span by reduction of both spanwise flow and strength of the tip vortex. The tubercles provide a bio-inspired design that has commercial viability for wing-like structures. Control of passive flow has the advantages of eliminating complex, costly, high-maintenance, and heavy control mechanisms, while improving performance for lifting bodies in air and water. The tubercles on the leading edge can be applied to the design of watercraft, aircraft, ventilation fans, and windmills.

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This work is devoted to the numerical simulation of acoustic emissions characterizing turbojet engines, a subject that is relevant for the more general purpose of aircraft noise prevision and reduction. More precisely, this study assesses the ability of a structured/time-domain computational aeroacoustics method to address realistic problems of engine noise prediction. To that end, we numerically simulate and analyze aft-fan-noise emissions characterizing a full three-dimensional exhaust (with its pylon and internal bifurcations), with that exhaust influenced by representative (takeoff) flight conditions and assigned relevant fan-noise modal contents (of high azimuthal order/ frequency). From a physical point of view, the results highlight how far the installation effects induced by the complex geometry/flow of an engine can affect its fan-noise emission. From a more methodological point of view, these outcomes indirectly show that computational aeroacoustics methods can be used to not only accurately predict engine noise emissions, but to also investigate the physics underlying them. Finally, these results also tend to indicate that computational aeroacoustics structured methods such as the one used here are mature enough to deal with industrial-like engine noise problems.

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This work, realized in the framework of the European project TurboNoiseBB, presents an advanced aeroacoustic design methodology of Outlet Guide Vanes (OGVs) with leading edge serrations, including details on their broadband noise and aerodynamic performance. The serrated OGV corresponds to a modified stator from an aeroengine fan stage tested at the AneCom AeroTest’s facility (Germany). Sinusoidal leading edge patterns with varying amplitude and wavelength along the span are designed in collaboration with Safran Aircraft Engines. Serrations are adjusted to account for the turbulence characteristics provided by Reynolds-Averaged Navier–Stokes (RANS) calculations. Optimal parameters are found using simple design rules discussed in this paper. Down selection of serrated OGV designs (patent pending) is conducted through a RANS control of aerodynamic performances and in accordance with industrial specifications, ensuring acceptable penalties on the loss coefficient and isentropic efficiency. Broadband noise simulations are performed using a computational aeroacoustic (CAA) code that solves the linearized Euler equations with a synthetic turbulence model. Additionally, the acoustic response of the serrated leading edge airfoils is also estimated using the most relevant analytical formulation in the literature, based on the Wiener–Hopf technique. Numerical predictions at approach conditions are compared to available experimental measurements (on the untreated baseline case) and analytical Amiet-based and Wiener–Hopf solutions, showing satisfactory agreement in the sound power spectrum in the bypass duct. Finally, the acoustic performances estimated at the design stage are numerically assessed by both the CAA and Wiener–Hopf methods, providing around 2.5 dB and 3.5 dB reduction in the overall power level, respectively.

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A Lattice-Boltzmann Method (LBM) based approach is used to perform transient, explicit and compressible CFD/CAA simulations on the Advanced Noise Control Fan (ANCF) configuration. The complete 3-D ducted rotor/stator model including all the geometrical details and the truly rotating rotor is simulated. Detailed near and far-field measurements conducted at the NASA Glenn research center are used to validate the simulation results. The measured and predicted sound pressure levels at the far-field microphones are compared and both show the presence of broadband noise and sharp peaks which frequencies depend on the number of rotor blades and the angular velocity of the rotor. The 3-D duct acoustics modes observed in experiments are also captured in the 3-D transient CFD/CAA calculation and detailed analyses of the results are presented. The main circumferential modes predicted from the number of rotor blades and stator vanes are recovered in both experimental and simulation modal decompositions.

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This work presents a numerical prediction of the tonal noise generation in a single-stage, axial flow fan, using a hybrid approach that first calculates the noise sources (generation) using conventional computational fluid dynamics (CFD) techniques, and then estimates the noise level in the blower far-field region (propagation) by means of an aeroacoustic analogy. As a starting point, an unsteady three-dimensional full-annulus simulation of the internal flow is carried out, using a wall-modelled large eddy simulation (WMLES) scheme for the turbulence closure to identify the acoustic sources. A well-tested commercial CFD package, FLUENT, was employed for that purpose, so a complete set of unsteady forces exerted over the blades was calculated. Following, a generalization of Lighthill's aeroacoustic analogy, the so-called Ffowcs Williams and Hawkings (FFWH) aeroacoustic analogy, was numerically implemented using a C++algorithm to resolve an integral formulation of the free-field FFWH wave equation, where CFD data are included in the source terms. The major contribution was expected to be found in the estimation of the tonal noise levels, directly linked to the intensity of the stator—rotor interaction phenomena. Additionally, intensive experimental measurements in the noise propagation region of the fan were conducted, in order to validate the numerical study. A reasonable agreement was found in the tonal noise spectra, although important discrepancies appeared due to the attenuation produced by the fan casing, not considered in the numerical model. Although limitations in the current computational resources led to the use of a relatively coarse mesh in the CFD modelling, the numerical study provided valuable information about the particular influence of the tonal noise sources, estimating accordingly overall experimental trends, and showing the potentiality of numerical tools to deal with noise control for designers and researchers.

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Following large efforts to reduce tone noise during the last decades in modern high-bypass ratio turbofans, fan broadband noise reduction has become now an industrial priority. A hybrid computational method providing source-to-far-field predictions of broadband noise due to rotor-stator interaction is presented. The acoustic model is based on the loading term of the FWH (Ffowcs Williams and Hawkings) equation with a modal Green's function valid for an infinite annular duct, and a Kirchhoff approximation for the free-field radiation. The aerodynamic sources on the airfoils required by the model are expected to be directly issued from a LES (Large Eddy Simulation) computation. The method is applied to a simplified configuration tested in a laboratory rig. The first part of the study is concerned with the assessment of in- duct acoustic field. Usual assumptions about coherence and energy distribution between the acoustic modes are analyzed. PSD (Power Spectrum Density) are calculated through several ways. The second part is focused on the ability to generate an equivalent PSD by means of equivalent source distributions. The purpose is to validate a practical way for coupling LES with Computational Aero-Acoustics Euler solver, in order to include realistic geometry and mean flow effects.

Aeroacoustic simulation of a ring rotor in presence of a uniform inlet ow is presented. An unsteady RANS simulation with a compressible solver is used to compute the ow eld and identify the acoustic sources on the rotor. The tip clearance recirculation shows upstream vortices that appear to impact the rotor blades creating the main source of unsteadiness. Since those vortices rotate at a lower speed than the rotor, the impact frequency implied is shown to be di erent than the blade passing frequency. Besides the aerodynamic simulation, the acoustic signature of this rotor is computed by propagating the noise sources located on the rotor surfaces using two methods: a Ffowcs-Williams & Hawkings analogy in the time-domain, as well as an analytical model in the frequencydomain based on the compact rotating dipole formulation. A comparison with experimental results con rms the aeroacoustic phenomena are well captured and properly propagated by the acoustic codes.

This paper presents results of a research project on active control of the blade passage frequency tone of an axial fan. The secondary sound field is generated by aeroacoustic sources, which are produced by actively controlling the flow around the impeller blade tips. Both amplitude and phase can be controlled in such a way that a destructive superposition with the primary sound field is possible. The flow distortions can be achieved by using different actuators; results using steady and unsteady jets of compressed air and piezo-electric actuators are presented.

An advanced model turbofan was tested in the NASA Glenn 9-by 15-Foot Low Speed Wind Tunnel (9x15 LSWT) to explore far field acoustic effects of increased bypass nozzle area. This fan stage test was part of the NASA Glenn Fan Broadband Source Diagnostic Test, second entry (SDT2) which acquired aeroacoustic results over a range of test conditions. The baseline nozzle was sized to produce maximum stage performance at cruise condition. However, the wind tunnel testing is conducted near sea level condition. Therefore, in order to simulate and obtain performance at other operating conditions, two additional nozzles were designed and tested one with +5 percent increase in weight flow (+5.4 percent increase in nozzle area compared with the baseline nozzle), sized to simulate the performance at the stage design point (takeoff) condition, and the other with a +7.5 percent increase in weight flow (+10.9 percent increase in nozzle area) sized for maximum weight flow with a fixed nozzle at sea level condition. Measured acoustic benefits with increased nozzle area were very encouraging, showing overall sound power level (OAPWL) reductions of 2 or more dB while the stage thrust actually increased by 2 to 3 percent except for the most open nozzle at takeoff rotor speed where stage performance decreased. Effective perceived noise levels for a 1500 ft engine flyover and 3.35 scale factor showed a similar noise reduction of 2 or more EPNdB. Noise reductions, principally in the level of broadband noise, were observed everywhere in the far field. Laser Doppler Velocimetry measurements taken downstream of the rotor showed that the total turbulent velocity decreased with increasing nozzle flow, which may explain the reduced rotor broadband noise levels.

This paper is concerned with the simulation of the unsteady turbulent flow and the aerodynamic tonal noise due to pressure fluctuations on the casing wall. Three-dimensional numerical simulations of the complete unsteady flow on the whole impeller-volute configuration were carried out using computational fluid dynamics (CFD) techniques. Pressure fluctuations on the casing wall were obtained, and the blade passing frequency (BPF) component was extracted to be modeled as the dipole source term of the wave equation. In a companion paper, the pressure fluctuations served as the external excitation to the casing vibration. Multi-domain direct boundary element method (BEM) was used to simulate the noise radiation with two domains representing the interior and exterior fields of the volute respectively, in order to take account of the sound scattering effect by the volute casing. Results showed that the dipole on the volute tongue surface was the most dominant noise source of the fan. Sloping-edge volute tongue was introduced to reduce BPF noise radiation through phase cancellation between the dipole sources over the volute tongue.

This paper presents the findings of an investigation on the use of several blade-tip configurations (modified by the addition of various end plates at the blade tip) for passive noise control in industrial fans. Utilizing an experimental technique developed to investigate noise sources along the radius of the blades, together with cross-correlation and coherence analyses of the near field and far field, the modified blade-tip configurations are shown to reduce the rotor-only aeroacoustic signature of the fan as a direct consequence of changes induced in tip-leakage flow behavior. These changes in the nature of flow mechanisms in the region of the blade tip are correlated with the spanwise noise sources, and their role in the creation of overall acoustic emissions is thus clarified. The tip-leakage flow structures are analyzed to identify their contribution to overall noise and interaction with other noise sources. Coherence spectra are also analyzed to investigate the relevance of the noise sources. The cross-correlations reveal distinctive acoustic signatures that are described in detail. The methodology has been demonstrated to be effective in identifying (i) the blade-tip configuration with the best acoustic performance, and (ii) other significant noise sources along the blade span. The modified tip configurations are shown to have a significant effect on the multiple vortex behavior of leakage flow, especially with respect to the near-wall fluid-flow paths on both blade surfaces. The reduction in fan acoustic emissions is assessed and correlated with the control of tip-leakage flows achieved by the modified blade tips.

This paper discusses the aeroacoustic aspects of the design, construction and testing of an all-electric ducted fan propulsion module for future electric aircraft. An overview of the propulsor aerodynamic design is provided. Acoustic measurements made with a prototype sub-scale unit in an anechoic chamber are reported, and measurement results are presented for far-field spectra, tonal and broadband directivities at a range of rotational speeds. It is shown that broadband noise is the dominant contributor to the sub-scale unit noise. A psychoacoustic investigation of the measured far-field radiation is conducted using selected Sound Quality Metrics, and it is shown that both Zwicker's Psychoacoustic Annoyance and Loudness scale with rotational speed at all angles.

The results of the multidisciplinary optimization of a contra-rotating fan have been taken as the basis for the study of different features of a wake interaction noise model, which influence the prediction and hence drive the optimization procedure towards the goal of noise reduction. The source and propagation effects have been considered separately. First, the effect of modelling the source either with a parallel or with a skew gust formulation, based on Amiet’s theory, has been investigated. Then, the propagation formula has been modified to take into account the effect of the geometry of the blades on the retarded time of the emission.

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Unsteady Reynolds Averaged Navier-Stokes(URANS) and Large Eddy Simulation(LES) simulation of an axial flow fan are calculated upon same conditions and computational grids in order to study aeroacoustic noise of an axial flow fan numerically. Results of computed performance and predicted noise are compared with those of measurement. Both performances show accurate results with a significant difference of less than 5%. However, noise of LES result is more close to measured noise qualitatively than URANS. Levels of tonal noises of both LES and URANS are quite similar with those of measured at BPF(Blade Passing Frequency) in sound spectrum. However, as leading edge separation and tip vortex shedding phenomena of LES are showed more clearly than those of URANS, sound level of broadband noise of LES corresponds better than that of URANS, especially.

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Modern high-speed turbo-machinery such as compressors and gas turbines can generate high level airborne noise from their fans/impellers. Here, the noise source locations and radiation characteristics of an open fan are predicted by using a Computational Aeroacoustic (CAA) model of the fan and compared to the experimental results obtained by using a Nearfield Acoustical Holography (NAH) method. The CAA model is built by using a commercial software package, ANSYS Fluent. In this model, the acoustic source data is extracted from a transient Computational Fluid Dynamic (CFD) analysis based on an unsteady k-I turbulence model. The NAH method is applied to sound pressure data measured by using an 8×8 microphone array to visualize the three-dimensional sound pressure fields. In addition, twelve reference microphones are used to decompose twelve incoherent partial sound pressure fields from the measured data. The CAA-predicted sound fields indicate that the fan noise sources consist of a combination of monopoles at the first blade passing frequency and its higher harmonics. The CAA model can be used to predict the sound pressure fields, radiated from the open fan, which agree well with the measured results in a wide frequency span.

A final objective of this study is to develop a tool to predict aeroacoustics noise radiated from a low-speed fan, and its reduction. Aeroacoustics noise that is radiated from a low-speed axial flow fan, with a six-blades rotor installed in a casing duct, is predicted by an one-way coupled analysis of the computation of the unsteady flow in the ducted fan and computation of the sound radiated to the ambient air. The former is performed by our original code, FrontFlow/blue, which is based on Large Eddy Simulation (LES). The latter is performed by using a commercial code, SYSNOISE, which computes the sound fields in the frequency domain. The following three cases of computations are performed for LES with different flow field configurations and/or grid resolutions: a coarse mesh without the struts located, in the actual fan, upstream of the rotor blades, a fine mesh without the struts, and a coarse mesh with the struts. The first two test cases are intended to investigate the effects of the mesh resolution on the prediction accuracy of the unsteady flow field, especially we intended to capture unsteadiness in turbulent boundary layer (TBL) in the second test case with the computational mesh composed of about 30 millions hexahedral elements. The fine mesh LES successfully reproduced the transition to TBL on the suction surface of the rotor blades and gives better, when compared with the results from the coarse mesh LES, agreements with measurements in terms of Euler’s. The final case is used for providing acoustical input data of the sound source. A reasonable agreement is obtained between the predicted and measured sound pressure level evaluated at 1.5 m upstream of the blade center.

Mathematical formulations of the unsteady three-dimensional flowfield induced by a rotating annular cascade interacting with an oncoming periodic gust and disturbances from an oscillating actuator surface composed as a part of the duct wall are presented on the basis of a linearized unsteady lifting surface theory. The problem of suppressing the tone noise due to interaction of the rotor with the gust by means of the actuator motion is studied. Theoretical analysis with numerical calculations is conducted for a simple harmonic sinusoidal gust, and a simple harmonic sinusoidal circumferential wave form of the actuator motion and optimum conditions of the actuator motion are investigated. There are substantial differences in the optimum phase and amplitude of the actuator motion between the conditions of suppressing the upstream and downstream acoustic powers. In the case of multiple cut-on duct modes, the actuator motions of the cut-off circumferential wave numbers are desirable to effectively suppress the total acoustic powers.

Aerodynamic and aeroacoustic performance experiments were carried out on four- and eight bladed, 1.542 m diameter, axial flow cooling fans, with constant solidity and hub-to-tip ratio. Tests were conducted in an ISO5801, Type A Fan Test facility. The tip gap (TG) was reduced from 4 mm (0.26% fan diameter) to 2 mm (0.13% fan diameter), to 0 mm, for both fan configurations. The noise profile of each fan configuration at the same TG over the whole volumetric flow rate spectrum was compared to each other. The 4 mm (0.26%) TG is used as a baseline to measure the nett increase or decrease in sound levels. Noise emissions decreased as the TG was reduced. It is discovered that the four bladed fan configuration had lower noise emissions than the eight bladed fan configuration at all blade tip clearances at design flow rate. It is concluded that reducing the TG and number of blades, at constant solidity, reduces sound emissions. The 0 mm TG for the four bladed fan produced the greatest reduction in noise emissions. An increase in fan total-to-static performance is observed when reducing the TG for both fan configurations.

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This dissertation investigates the effect of airfoil steady loading on the sound generated by the interaction of an isolated, zero-thickness airfoil with a high-frequency convected disturbance. The analysis is based on a linearization of the inviscid equations of motion about a nonuniform mean flow. The mean flow is assumed to be two-dimensional and subsonic. Throughout most of the dissertation, we assume that the Mach number is 0(1), though in one section we concentrate on the leading-edge region and study the behavior of the sound field as the Mach number tends to zero. The small parameter representing the amount of airfoil camber and incidence angle, and the large parameter representing the ratio of airfoil chord to disturbance wavelength, are utilized in a singular perturbation analysis. The analysis shows that essentially all of the sound is generated at the leading and trailing edges, in regions the size of the disturbance wavelength. The solution in the local-leading-edge region reveals several sound-generating mechanisms which do not exist for an airfoil with no mean loading. These mechanisms are not present at the trailing edge; the trailing edge is important only as a scatterer of the sound produced at the leading edge. The propagation of sound away from the airfoil edges is described by geometric acoustics, with the amplitude varying on the scale of the airfoil chord and the phase varying on the much smaller scale of the disturbance wavelength. In addition, a diffraction-type transition region exists downstream of the airfoil. Calculations of radiated acoustic power show that the sound field depends strongly on Mach number, gust characteristics, and airfoil steady loading. Small changes in these properties can produce large changes in radiated power levels. Most importantly, we find that the amount of power radiated correlates very well with the strength of the mean flow around the leading edge.

The purposes of the subject test were to identify and quantify the mechanisms by which fan broadband noise is produced, and to assess the validity of such theoretical models of those mechanisms as may be available. The test was conducted with the Boeing 18-inch fan rig in the Boeing Low-Speed Aeroacoustic Facility (LSAF). The rig was designed to be particularly clean and geometrically simple to facilitate theoretical modeling and to minimize sources if interferring noise. The inlet is cylindrical and is equipped with a boundary layer suction system. The fan is typical of modern high-by-pass ratio designs, but is capable of operating with or without fan exit guide vanes (sators), and there is only a single flow stream. Fan loading and tip clearance are adjustable. Instrumentation included measurements of fan performance, the unsteady flow field incident on the fan and stators, and far-field and in-duct acoustic fields. The acoustic results were manipulated to estimate the noise generated by different sources. Significant fan broadband noise was found to come from the rotor self-noise as measured with clean inflow and no boundary layer. The rotor tip clearance affected rotor self-noise somewhat. The interaction of the rotor with inlet boundary layer turbulence is also a significant source, and is strongly affected by rotor tip clearance. High level noise can be generated by a high-order nonuniformity rotating at a fraction of the fan speed, at least when tip clearance and loading are both large. Stator-generated noise is the loudest of the significant sources, by a small margin, at least on this rig. Stator noise is significantly affected by propagation through the fan.

The aim of this paper is to present a computational method to predict the aeroacoustic noise in ducted fans. Here, the method is applied to an axial fan running at 1980 rpm in a circular duct. Two commercial softwares, FLUENT and LMS SYSNOISE, are employed for this purpose. Unsteady flow analysis is performed with Large Eddy Simulation (LES) using FLUENT and then passed to LMS Sysnoise in order to compute the acoustic radiation. The numerically obtained acoustic field around the duct is compared with the experimental data and fairly good agreement is observed.

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We have developed a prediction model for the overall level of aeroacoustic noise generated by cross-flow fans. It is based on two assumptions: the velocities along the outside edge of the impeller have an especially close relation to the noise levels, and the noise levels are in proportion to the sixth power of the relative velocities at the edge of the blade. A computational fluid dynamics is used to obtain the necessary velocity-field data for this prediction model. The predicted noise levels of a test impeller for different flow coefficients are in good agreement with the measured results. This means that variations in noise levels with the flow coefficient can be described accurately by the prediction model, which should prove to be a useful tool for speeding up the development of silent cross-flow fans.

A hybrid aerodynamic-aeroacoustic method has been developed and applied to predicting the tonal noise of a Boeing ducted fan model tested at low speed. The steady-state threedimensional flow field was obtained by solving Navier-Stokes equations using an explicit, timemarching, finite volume, multigrid, multiblock, and central difference algorithm. With the input of near field aerodynamics, the radiated acoustic field from the ducted fan was computed by using a Galerkin finite element procedure with conventional finite elements in the near field and wave envelope elements in the far field. Three cases were studied including the effect of boundary layer suction on the inner cowl wall. Aerodynamic calculations show that acoustic waves are captured in the inlet duct. The predicted noise directivity and sound pressure levels are in good agreement with Boeing measured data.

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Obtaining the right pitch in turbomachinery blading is crucial to efficient and successful operations. Engineers adjust the rotor’s pitch angle to control the production or absorption of power. Even for low speed fans this is a promising tool. This paper focuses on the inception and the evolution of the flow instabilities in the tip region which drive the stall onset in low speed axial fans. The authors conducted an experimental study to investigate the inception patterns of rotating stall evolution at different rotor blade stagger-angle settings with the aim of speculating on stable operating margin. The authors drove the fan to stall at the design stagger-angle setting and then operated the variable pitch mechanism in order to recover the unstable operation. They measured pressure fluctuations in the tip region of the low-speed axial-flow fan fitted with a variable pitch in motion mechanism, with flush mounted probes. The authors studied the flow mechanisms for spike and modal stall inceptions in this low-speed axial-flow fan which showed relatively small tip clearance. The authors cross-correlated the pressure fluctuations and analyzed the cross-spectra in order to clarify blade pitch, end wall flow, and tip-leakage flow influences on stall inception during the transient at the rotor blades’ different stagger-angle settings. The authors observed a rotating instability near the maximum pressure-rise point at both design and low stagger-angle settings. The stall inception patterns were a spike type at the design stagger-angle setting as a result of the interaction between the incoming flow, tip-leakage flow and end wall backflow.

Comprehensive measurements of the spinning acoustic mode structure in the inlet of the advanced ducted propeller were obtained using a unique method that was first proposed by Sofrin. A continuously rotating microphone system was employed. Three inlet configurations with cut-on as well as cut-off stator vane sets were tested. The cut-off stator was designed to suppress all modes at the blade passing frequency. Rotating rake measurements indicate that several extraneous circumferential modes, possibly due to the interaction between the rotor and small interruptions in the casing tip treatment, were present. The cut-on stator produced the expected circumferential modes plus higher levels of the unexpected modes seen with the cut-off stator. HE next generation of fan engines will likely employ a marriage of turbofan and propeller technologies to achieve significant noise and fuel consumption reductions. The ad- vanced ducted propeller (ADP) model used in this investi- gation was designed and built by Pratt and Whitney, a Di- vision of United Technologies, and tested in the NASA Lewis 9- by 15-ft Anechoic Wind Tunnel. Typical of propeller tech- nology, the ADP allows for the in-flight adjustment of the blade pitch angle. This provides reverse thrust and optimum performance over a wide range of conditions. The duct pro- vides the noise suppression advantage of a conventional fan engine. Since future engines are expected to use still higher bypass ratios, fan noise is likely to be the dominant engine source. One of the most important features of fan tone noise is its modal structure. Knowledge of these spinning modes helps to identify the generation mechanism, control duct propa- gation (thus, mode knowledge is needed for acoustic treat- ment design) and control far-field radiation. Previous at- tempts at direct mode measurements1'3 have faced formidable practical difficulties such as: very large axial and circumfer- ential arrays of wall microphones that are not practical for the short ducts of ultrahigh bypass engines, and radial mea- surements upstream of the fan that introduce a wake that interacts with the rotor, thus causing extraneous modes. A continuously rotating microphone technique first proposed by Sofrin4 overcomes the problem of wake-generate d modes, reduces the number of microphones and the duct length re- quired. This technique has been implemented for the first time in this investigation. Two important features of this tech- nique are as follows:

Axial flow fans are commonly used for a system or machinery cooling process. It also used for ventilating warehouses, factories, and garages. In the fan manufacturing industry, the demand for varying fan operating points makes design parameters complicated because many design parameters affect the fan performance. This study combines the deep neural network (DNN) with a genetic algorithm (GA) for axial flow design and development. The characteristic fan curve (P-Q Curve) can be generated when the relevant fan parameters are imported into this system. The system parameters can be adjusted to achieve the required characteristic curve. After the wind tunnel test is performed for verification, the data are integrated and corrected to reduce manufacturing costs and design time. This study discusses a small axial flow fan NACA and analyzes fan features, such as the blade root chord length, blade tip chord length, pitch angle, twist angle, fan diameter, and blade number. Afterwards, the wind tunnel performance test was performed and the fan performance curve obtained. The feature and performance test data were discussed using deep learning. The Python programming language was used for programming and the data were trained repeatedly. The greater the number of parameter data, the more accurate the prediction. Whether the performance condition is met could be learnt from the training result. All parameters were calculated using a genetic algorithm. The optimized fan features and performance were screened out to implement the intelligent fan design. This method can solve many fan suppliers’ fan design problems.

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Abstract In the current study, the tandem blade technology is applied to an supersonic throughflow fan (STFF) tandem cascade for the first time and a 2D STFF tandem cascade is preliminarily designed. Through the modification design of the tandem airfoils and their configuration (axial overlap (AO) and percent pitch (PP)), the coefficients of total pressure loss and loading are reduced by 4% and 8.58%, respectively. Furthermore, the impact of tandem configurations on the performance is parametrically investigated by numerical simulations. The results indicate that compared with AO, the performance under design incidence is more sensitive to PP except for the cases with PP exceeding a threshold value (1.15). PP dominates the loss and load by controlling the evolution of the FB wake and the shock structure of FB and the rear one of the tandem blade (RB), while AO mainly adjusts the entire shock system structure through the change of virtual shape, resulting in the variation in load distribution between FB and RB. It is worth noting that the overall loading and the total loss remain unchanged with increasing AO except for the tandem configurations (PP = 1.05, AO ≤ −0.01), which make the flow structure in the gap region undergo a fundamental change. With the optimal tandem configuration (PP = 1.05, AO = −0.01) and the modified tandem blades (the ratios of chord length and camber for FB over RB are 0.67 and 0.5, respectively), the total pressure loss coefficient is further reduced by 19.7% in comparison with the preliminary tandem design.

Fan and compressor research projects carried out at GE Aircraft Engines under NASA sponsorship are described in this paper. Four 1400-fps-tip-speed rotors designed with different airfoil shapes were found to have comparable stall lines but different efficiency trends. A stator placed behind one of these affected its performance somewhat. Adjustments of variable camber inlet guide vanes placed ahead of a 1500fps stage were found to affect its pumping capability without much affecting its stall line. For the Quiet Engine Program (QEP), two 1160-fps fans and one 1550-fps fan were tested. Development of the high-speed fan revealed the effects on performance of airfoil shape and part-span shroud blockage. The 950-fps variable-pitch fan for the Quiet Clean Short-haul Experimental Engine (QCSEE) demonstrated reverse thrust capabilities and a novel method of avoiding large core inlet pressure losses during reverse thrust operation. The 1350-fps Energy Efficient Engine (E3) fan demonstrated excellent performance with a novel quarter-stage arrangement that eliminated the need for interspool bleed while giving good dirt removal potential. The E3 compressor program employed Low Speed Research Compressor tests to identify the most appropriate blading type. High-speed rig tests and engine tests were then used to develop this 23:1-spool-pressure-ratio compressor. Research on casing boundary layer control through bleeding and blowing led to the discovery that irregular casing geometries usually give stall line enhancements even without auxiliary air circuits. Some of the resulting casing treatment research is reported herein. Instances in which NASA-sponsored research has affected GE Aircraft Engine products are pointed out.

Design criteria as well as a general description are provided for the first full-scale variable pitch fan engine tested in this country. The test facility for this 6700 Ib thrust engine is defined, and a summary of the test program is presented. Aerodynamic, acoustic, and structural data from the initial test phase are discussed. A ground adjustable mechanism was used to set fan blade angle for the first series of tests. A second test phase was conducted with a dynamic pitch change capability incorporated in the engine; the significance of reverse transient results are examined.

Fan and compressor research projects carried out at GE Aircraft Engines under NASA sponsorship are described in this paper. Four 1400-fps-tip-speed rotors designed with different airfoil shapes were found to have comparable stall lines but different efficiency trends. A stator placed behind one of these affected its performance somewhat. Adjustments of variable camber inlet guide vanes placed ahead of a 1500 fps stage were found to affect its pumping capability without much affecting its stall line. For the Quiet Engine Program (QEP), two 1160-fps fans and one 1550-fps fan were tested. Development of the high-speed fan revealed the effects on performance of airfoil shape and part-span shroud blockage. The 950-fps variable-pitch fan for the Quiet Clean Short-Haul Experimental Engine (QCSEE) demonstrated reverse thrust capabilities and a novel method of avoiding large core inlet pressure losses during reverse thrust operation. The 1350-fps Energy Efficient Engine (E3) fan demonstrated excellent performance with a novel quarter-stage arrangement that eliminated the need for inter-spool bleed while giving good dirt removal potential. The E3 compressor program employed Low Speed Research Compressor tests to identify the most appropriate blading type. High-speed rig tests and engine tests were then used to develop this 23:1-spool-pressure-ratio compressor. Research on casing boundary layer control through bleeding and blowing led to the discovery that irregular casing geometries usually give stall line enhancements even without auxiliary air circuits. Some of the resulting casing treatment research is reported herein. Instances in which NASA-sponsored research has affected GE Aircraft Engine products are pointed out.

Car air-conditioners consist of a blower unit and a heater unit. A blower unit sends wind to a heater unit, and a heater unit adjusts the temperature inside the vehicle. Blower units of car air-conditioners are required to be smaller, lighter, noiseless, and power-saving. However, it is difficult and expensive to predict the noise directly by computational fluid dynamics simulation. Hereupon, this study employs an indirect noise prediction method based on a noise prediction theory to evaluate noise for blower units inexpensively. This method is investigated through a comparison with actual sound pressure level measurement. Then, using this method, this study moves to design optimization of a blower unit of car air-conditioners. The optimization aims to improve total pressure efficiency and sound pressure level from the current design that has been employed for a real commercial vehicle. This study employs a genetic algorithm to explore global optima in a two-objective problem. The present genetic algorithm is assisted by the Kriging surrogate model to reduce computational cost required for evaluating objective functions. The optimization results indicate that the optimized blower unit involves a multi-blade fan with the high chord-pitch ratio to decrease the loss of total pressure efficiency, which is often induced by the flow separation on the blade and the swirling flow on the meridional plane. In addition, the sound pressure level of blower unit can be reduced by decreasing the local flow velocity on the meridian plane due to a blockage factor. A blower unit, which has a scroll with a large tongue angle, shows high total pressure efficiency because the increase in eddy loss is suppressed at the tongue. They suggest the importance of the matching of multi-blade fan and scroll to achieve the good overall performance of a blower unit.

No abstract

Acoustic and aerodynamic data for a 1.83-meter (6-ft.) diameter fan suitable for a quiet engine for short-takeoff-and-landing (STOL) aircraft are documented. The QF-9 rotor blades had an adjustable pitch feature which provided a means for testing at several rotor blade setting angles, including one for reverse thrust. The fan stage incorporated features for low noise. Far-field noise around the fan was measured without acoustic suppression over a range of operating conditions for six different rotor blade setting angles in the forward thrust configuration, and for one in the reverse configuration. Complete results of one-third-octave band analysis of the data are presented in tabular form. Also included are power spectra, data referred to the source, and sideline perceived noise levels.

The goal of this study is the simulation of the flow inside a rotor with elliptic airfoils, where the Kutta condition cannot be satisfied. This work develops a three-dimensional numerical modelling of a monoplane axial jet fan with symmetric blades. The three-dimensional model includes tip clearance gridding and turbulence modelling based on high-order Reynolds-averaged Navier—Stokes (RANS) schemes. The flow patterns inside the blade passage and the wake-core structure will be studied at design operating conditions. Also, the interaction of the tip leakage flow with blade-to-blade structures will be analysed in detail. The investigation shows how the tip leakage vortex modifies the blade loading on the suction surface. The leakage flow rolls up in a vortical structure at the suction side, establishing a mixing mechanism that produces a low-axial velocity region. As a result, the adverse pressure gradient is enhanced and a major flow separation overcomes. This feature is especially critical in the case of a rotor with symmetric blades, where the flow is always detached at the trailing edge. The simulation is carried out using a commercial code, FLUENT, which resolves the Navier—Stokes set of equations. A high dense mesh is introduced in the model, so tip leakage is expected to be well captured. Different turbulence models have been tested in order to determine the most accurate choice. It is shown that a linear Reynolds stress model provides velocity distributions more adjusted to experimental data. This suitable prediction for rotating flow passages is a consequence of the characteristics of the model: consideration of anisotropic turbulence and direct inclusion of curvature and rotation effects in the transport equations. Therefore, swirl effects of the tip vortex can be modelled correctly. The numerical results are compared with previous experimental data of velocity fields to validate the simulation. In particular, the instantaneous wake flow structure was measured with a two hot-wire anemometer. Axial and tangential velocity profiles were obtained after pitch averaging the time-resolved flow patterns.

Noise emitted from an axial fan is classiffied into two types of noise, that is, rotational and turbulent noise. The former is due to the radiator fan, which is one of the major components of noise generated in an engine compartment, and consists of many efforts have been made to reduce it. In this paper the mechanism of the rotational noise of an axial fan having blades of unequal pitch angles is studied experimentally. By adjusting the attack angle of each blade with the blade pitch and accelerating the flow in narrower passages, the rotational noise was found to be decreased.

The supersonic through-flow variable-pitch tandem fan offers significant potential to expand the acceptable inflow range of the fan. However, owing to its higher degree of freedom, the adjustment relationship between the front and rear blades needs further clarification. This study uses numerical simulations to explore the adjustment and loss mechanisms of the rear blade stagger angle in a variable-pitch tandem cascade across different operating modes. In the transonic mode, cascade performance changes monotonically with the rear blade stagger angle. A larger stagger angle can significantly reduce the shock boundary layer interaction on the suction side of the rear blade, while weakening the maximum boost capacity of the cascade. In the supersonic through-flow mode, the favorable pressure gradient enables the rear blade to operate at a smaller positive incidence, improving its flow turning ability and alignment between the inlet metal angle of the rear blade and the inflow angle of the front blade under positive incidence conditions. In the high-speed windmilling mode, it is crucial to achieve a balance between the separation at the trailing edge of the suction side of the rear blade and the shock-induced separation on the pressure side. Notably, the optimal trend of the rear blade stagger angle adjustment in these two modes shows an inverse relationship.

Variable pitch propellers, once confined to turboprop engines, are now revolutionizing turbofan applications. Recent breakthroughs in materials and technology, exemplified by Pratt &amp; Whitney’s geared turbofan engine, underscore the practicality of variable pitch systems. Ongoing research promises to extend their adoption across diverse engine types, significantly enhancing safety and performance. This study investigates a novel approach to enhance reverse thrust using dual-row radial fans with adjustable pitch angles. These fan blades exhibit geometry variations, combining features from both turbofan motor fan blades and turbo- propeller motor blades. The results are promising: this configuration nearly triples the thrust force, producing approximately 292.917 kilo-newtons. Moreover, it enables the generation of reverse thrust equivalent to 25.077 kilo- newtons. These enhancements are achieved while reducing blade rotational speed from 5200 revolutions per minute to 3200 revolutions per minute and inlet airspeed from 660 km/h (at maximum power) to 220 km/h. Additionally, a notable 11% reduction in noise level at the blade tips has been observed. This research sheds light on the potential of innovative fan blade designs to revolutionize reverse thrust capabilities in turbofan engines, contributing to safer and more efficient aircraft landings.

An externally driven, 1.2 pressure ratio full-scale fan stage with an adjustable pitch rotor was tested in an outdoor facility at the Lewis Research Center. Rotor pitch angles resulting in minimum sideline perceived noise levels are defined as a function of stage thrust. Thrust-corrected fan noise variations are examined for operation at constant thrust, rotor tip speed, and stage work coefficient. At constant stage thrust, reducing the rotor pitch angle below design values increased the fan noise with the greatest change occurring in the blade passing tone level. At constant fan speed the minimum noise occurred at a particular rotor pitch angle, which was not the minimum thrust condition. With constant stage work coefficient, rear quadrant noise increased at above-design speed conditions.

Background noise measurements were made of the acoustic environment in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel (40x80) at NASA Ames Research Center. The measurements were acquired subsequent to the 40x80 Aeroacoustic Modernization Project, which was undertaken to improve the anechoic characteristics of the 40x80's closed test section as well as reduce the levels of background noise in the facility. The resulting 40x80 anechoic environment was described by Soderman et. al., and the current paper describes the resulting 40x80 background noise, discusses the sources of the noise, and draws comparisons to previous 40x80 background noise levels measurements. At low wind speeds or low frequencies, the 40x80 background noise is dominated by the fan drive system. To obtain the lowest fan drive noise for a given tunnel condition, it is possible in the 40x80 to reduce the fans' rotational speed and adjust the fans' blade pitch, as described by Schmidtz et. al. This idea is not new, but has now been operationally implemented with modifications for increased power at low rotational speeds. At low to mid-frequencies and at higher wind speeds, the dominant noise mechanism was thought to be caused by the surface interface of the previous test section floor acoustic lining. In order to reduce this noise mechanism, the new test section floor lining was designed to resist the pumping of flow in and out of the space between the grating slats required to support heavy equipment. In addition, the lining/flow interface over the entire test section was designed to be smoother and quieter than the previous design. At high wind speeds or high frequencies, the dominant source of background noise in the 40x80 is believed to be caused by the response of the in-flow microphone probes (required by the nature of the closed test section) to the fluctuations in the freestream flow. The resulting background noise levels are also different for probes of various diameters and types. The inflow microphone support strut is also a source of background noise but this source's impact may be minimized by careful design of the strut. In the present paper, the mechanisms mentioned above are discussed in detail. Their frequency and velocity ranges of dominance are defined and the differences between past and current facility background noise levels are presented. This paper gives valuable information for those wishing to make acoustic measurements in the 40x80. With this report and an estimate of the noise levels produced by the noise source of interest, it should be possible to determine the signal-to-noise ratios and measurement locations to successfully perform aeroacoustic testing in the NASA Ames Research Center's 40- by 80-Foot Wind Tunnel.

The objective of the Stanford ASC project is to develop a framework able to perform multi-disciplinary, integrated simulations on massively parallel platforms. 4 This paper focuses on the turbomachinery computation and, in particular, on the physics of interaction of different turbomachinery components in the engine. Typical flow features such as tip and horse-shoe vortices as well as blade wakes will be discussed for these multi-component turbomachinery simulations. The compressor and turbine of a modern turbofan engine, Figure 1, typically have two counter-rotating concentric shafts to allow for different rotational speeds of their components as well as a reduction of net torque. The low-pressure parts rotate at a lower rate than the high-pressure components. Typical rotation rates are 5,000 to 7,000 RPM for the former and 15,000 to 20,000 RPM for the latter. The compressor and turbine themselves consist of a series of rotors and stators for which the blade counts are normally chosen such that no sector periodicity occurs. Combined with the inherently unsteady nature of turbomachinery flows due to the motion of the rotors, the full wheel geometry needs to be considered in a time accurate numerical simulation of the flow. The computational requirements for such a simulation are severe. The high-pressure compressor (HPC) alone consists of 5 stages (rotor/stator combinations) and 50 to 200 blade passages per stage. Since approximately a million nodes are required per blade passage to obtain a grid-converged Reynolds-Averaged Navier-Stokes (RANS) solution, the computational mesh for a full wheel HPC simulation contains 500 million to 1 billion nodes. The turbine consists of less stages due to the the favorable pressure gradient. However, a full wheel simulation still requires 150 million to 300 million nodes. The spatial mesh is to be integrated in time for 2,000 to 10,000 time steps, based on the estimate that 50 to 100 time steps are needed to resolve a blade passing, to remove the transient effects. Alone the full wheel unsteady HPC simulation will require 20 to 40 million CPU hours on today’s fastest computers. Adding the low-pressure compressor (LPC), fan as well as highand low-pressure turbine (HPT and LPT, respectively), the computational requirements are far beyond what is currently affordable for practical applications and therefore approximations are used to reduce the computational costs. The most widely-used industrial practice for solving turbomachinery problems is the mixing plane assumption. A circumferential averaging of the flow variables is applied at the interface between rotor and stator. These average quantities are then imposed as upstream and downstream values for the following and preceding blade rows respectively and a steady-state computation can be performed for both the rotor and the stator. Due to this averaging and the periodicity assumption only one blade passage needs to be simulated per blade row, independently of the blade counts. Although this assumption models the mean effect of the rotor/stator interaction, all the unsteady information is lost due to the averaging. An alternative approach used to perform an unsteady simulation is to chose a periodic sector of, for example 20o, where the blade counts are changed such that the full wheel can be split into 18 sections and periodicity conditions can be used. The pitch and chord of the blades then need to be adjusted to preserve the flow blockage. Because of these changes it is clear that only approximate information can be obtained

The need for thrust forces on an aircraft in flight propellers and jet propulsion propellers, jets and rockets compared source of thrust efficient propulsion in a fluid rockets aerofoils optimum angle of attack propeller blades variable pitch and constant speed propellers feathering reversible pitch propellers blade tip speed propeller reduction gears number of blades required contra rotating propellers altitude effects variable pitch and constant speed mechanisms the engine cycles the importance of compression two strokes and four strokes the practical four stroke engine poppet valve mechanisms sleeve valves inertia of moving parts balancing the reciprocating parts torsional oscillations turbojets .turboprops - an introduction turbofans, ducted fans and by-pass engines - an introduction the gas turbine cycle the compression process compression ratios and pressure ratios the effect of altitude on engine power the centrifugal supercharger exhaust turbines two-stage superchargers compression in the gas turbine compression by RAM compressor intake losses surging compressor characteristics the two-stage centrifugal compressor axial compressors compressor velocity diagrams free vortex flow constant reaction blades stall and surge starting the airflow adjustable guide vanes blow-off valves two spool compressors temperature effects fuels and combusion combustion in the piston engine detonation and octane ratings gas turbine fuels supplying the fuel to the combustion chambers induction the simple carburettor compensating devices correction for altitude icing injectors supplying the fuel to the gas turbine combustion in the gas turbine burners and combustion changers power, power limitations and power boostings transmission dynamometers radial and in-line piston engines expansion in the gas turbine turbines effect of free vortex flow on blade shape limiting conditions at the turbine radial flow turbines jet pipes boosting the thrust adjustable jet pipe nozzles turboprops turbofans thrust reversal intakes water/methanol injection engine cooling controls supercharger controls automatic boost control controls for the aircraft turbine limiting the speed pressure control anti-surge devices temperature control re-heat control electrical fuel control systems jet pipe temperature control complete electrical control control for a two spool engine with re-heat propulsion controls for supersonic flight conclusion.

Static and propulsive performance characteristics of ducted fan at zero angle of attack for several fan blade angles

The predictions of fan performance on the pressure and flow rate characteristics of the axial flow fans using the conventional computational flow dynamics (CFD) approaches generally show a large deviation of about 20–30% from the experimental results. This article modifies the conventional CFD approaches by engaging the flow resistance of the fan test bench on the downstream area of the computational domain. The downstream pressure and flow rate are adjusted iteratively during the computational process. The results show that the prediction deviations using this method can be reduced to at most 3%, which is a great improvement compared to the conventional method. The inter-blade flows of three axial flow fans with different blade angles of attack are subsequently studied using this method. The results show that the flow patterns are drastically sensitive to the variation of the blade angle of attack, and the fan performances are closely related to the inter-blade flow behaviors. In the pre-stall regime, inappropriately designed blade angle of attack would cause the inter-blade flows in the region near the blade tip and the flows in the tip clearance region to present larger lateral and smaller axial velocity components with recirculation bubbles near the blade trailing edges. These flow behaviors cause the degradation of the fan performance. In the stall regime, boundary layer separation occurs to the suction surface of fan blades. Large recirculation bubbles appear near the trailing edges of blades and cause blockage effect against the axial flows. For the fans with inappropriately designed blade angle of attack, reverse flows can even be observed in the inter-blade passages with huge recirculation bubbles attaching to the trailing edges of fan blades.

In this investigation an attempt is made to find the best hub to tip ratio, the maximum number of blades, and the best angle of attack of an axial fan with flat blades at a fixed rotational speed for a maximum mass flow rate in a steady and turbulent conditions. In this study the blade angles are varied from 30 to 70 degrees, the hub to tip ratio is varied from 0.2 to 0.4 and the number of blades are varied from 2 to 6 at a fixed hub rotational speed. The results show that, the maximum flow rate is achieved at a blade angle of attack of about 45 degrees for when the number of blades is set equal to 4 at most rotational velocities. The numerical results show that as the hub to tip ratio is decreased, the mass flow rate is increased. For a hub to tip ratio of 0.2, and an angle of attack around 45 degrees with 4 blades, a maximum mass flow rate is achieved.

Fans are used all over the world in a wide verity of industries and other purposes. Some of the important applications are in steam power station, ventilation system, cooling of electric motor and generator, and many industrial processes. Many researchers and engineers are making their efforts to design fans to fulfill the particular requirement of application in the most efficient way. The criterion of cost of fan, ease in manufacture and conservation of energy are other also to be considered in design. Several studies are available of various researchers in analysis and simulation of axial and centrifugal fans. Axial flow fans have also been designed and simulated by the researchers. Simulation of performance of axial flow fans and design of various blade sections of the axial flow fans have been studied experimentally or numerically. The present work comprises the numerical study of the axial flow fan section aerofoil. The objective of the study is to simulate the flow features around the aerofoil of particular design for three different values of the striking angle. The results are obtained using FLUENT in the form of velocity vectors at the leading edge, across the aerofoil and at the trailing edge. The contours of pressure and turbulence are also shown for the three cases.

Acceleration potential techniques from three-dimensional thin wing theory have been generalized for propeller and prop-fan analysis. Helicoidal reference surfaces take the place of the planar surface in wing theories; otherwise the theories are equivalent. The acoustic branch of the theory, including nonlinear source terms, extends and unifies frequency domain noise theories dating back to Gutin. For aerodynamic applications, it is shown that prop-fans satisfy well-known criteria for use of linearized theory at transonic speeds by virtue of small aspect ratio and small thickness ratio. The results are in the form of integral equations for downwash as functions of thickness and steady or unsteady loading distributions. For the case of no rotation, the kernel functions reduce to well-known kernels of wing theory. The analysis, within the restrictions of linearization , treats rigorously any planform and any flight condition including the combination of subsonic roots and supersonic tips typical of prop-fans. The effects of thickness, camber, angle of attack, sweep, offset, blade interference, and tip relief are all treated without approximation.

No abstract

This paper describes the prediction of broadband self noise from ducted fans. The source mechanism is assumed to be the interaction of the turbulent boundary layer with the trailing edges of the fan blades. The source levels are obtained from the measurements of self noise from isolated blades by Brooks, Pope and Marcolini and these are corrected to give the in duct sound power from a high solidity fan. It has been found that the blade surface pressures are not uncorrelated on each fan blade and corrections must be included for the scattering from multiple trailing edges. A method is introduced for coupling the modes in a circular duct to the modes of a linear cascade so that the sound power is not singular at the mode cut on frequencies. Results show that the in duct sound power scales with the fifth power of the fan speed at low Mach numbers, but this changes to the sixth power or greater at high Mach numbers. The angle of attack of the blade increases the self noise as 2.4 dB per degree and there are significant increases in low frequency noise when blade stall occurs.

An actuator duct model was installed into the WIND Navier-Stokes code. With this model, flow through fan rotors and fan exit guide vanes can be simulated without blade geometry. Flow turning, total pressure and total temperature changes across blade rows are controlled by body forces added to the Navier-Stokes equations. This model provides an affordable and relatively accurate prediction of a three-dimensional flow field through rotor and stator blade rows. A NASA Stage 35 compressor and a NASA 22 test rig flow were analyzed to quantify the ability of the actuator duct theory to represent blade rows. Favorable comparisons between predicted and measured total pressure, total temperature and swirl profiles indicated that the actuator duct logic was correctly installed in the WIND code. Comparisons of inlet separation angle-of-attack were made between test data and predictions using the actuator duct theory. The WIND code with the actuator duct model predicted higher separation angle-of-attack by an average of 2° for different fan speeds. The effect of the rotor on inlet flow separation was also determined by comparing the predictions of a flow-through nacelle with the predictions using the actuator duct to simulate the rotating fan. The comparison shows that the presence of the rotor increased separation free angle-of-attack over the flow-through nacelle which is consistent with the observation from the experiment. NOMENCLATURE

A detailed experimental study on the aerodynamic performance and noise emission of airfoils and fan blades with permeable leading edges under disturbed inflow conditions was performed. The airfoils and fan blades with permeable leading edges were made of an aluminum alloy using a powder bed fusion-based additive manufacturing process. In a first step, a wind-tunnel study was carried out. This consisted of detailed aerodynamic and aeroacoustic measurements on 16 airfoils with different permeable leading-edge designs that were performed for various flow speeds and geometric angles of attack. Based on the results from that study, unskewed fan blades with four different permeable leading-edge designs were manufactured in a second step. With the aim of reducing turbulence interaction noise of axial fans, the fans were examined with regard to their aerodynamic and acoustic properties under grid-generated turbulent inflow conditions. In a third step, a possible transfer of the observed noise emission from airfoils with permeable leading edge to that of fan blades was investigated. It was found that a notable broadband noise reduction can be transferred from airfoil applications to the sound spectra of axial fans. At the same time, the porous modifications can reduce the aerodynamic performance, and hence the fan efficiency.

Purpose The purpose of this paper is to explore a methodology that allows to represent turbomachinery rotating parts by replacing the blades with a body force field. The objective is to capture interactions between a fan and an air intake at reduced cost, as compared to full annulus unsteady computations. Design/methodology/approach The blade effects on the flow are taken into account by adding source terms to the Navier-Stokes equations. These source terms give the proper amount of flow turning, entropy, and blockage to the flow. Two different approaches are compared: the source terms can be computed using an analytic model, or they can directly be extracted from RANS computations with the blade’s geometry. Findings The methodology is first applied to an isolated rotor test case, which allows to show that blockage effects have a strong impact on the performance of the rotor. It is also found that the analytic body force model underestimates the mass flow in the blade row for choked conditions. Finally, the body force approach is used to capture the coupling between a fan and an air intake at high angle of attacks. A comparison with full annulus unsteady computations shows that the model adequately captures the potential effects of the fan on the air intake. Originality/value To the authors’ knowledge, it is the first time that the analytic model used in this paper is combined with the blockage source terms. Furthermore, the capability of the model to deal with flows in choked conditions was never assessed.

The Wells turbine rotor consists of several symmetric airfoil blades arranged around a central hub, and the stagger angle is 90 degrees. These characteristics simplify the total construction of OWC type wave energy converters. Although the Wells turbine is simple, the turbine produces a complicated flow field due to the peculiar arrangement of blades, which can rotate in the same direction irrespective of the oscillating airflow. In order to understand these flows, flow visualization is carried out with an oil-film method in the water tunnel. This research aims to analyze the mechanism of the 3-D flows around the turbine with the flow visualization. The flow visualization explained the influence of attack angle, the difference between fan-shaped and rectangular wings, and the sweep angle.

The aim of this article is to develop a three-dimensional computational model to simulate the traveling process of inlet distortion in fan and compressor with low calculated costs. The model is established based on the body force model in the framework of modern Computational Fluid Dynamics technology. The flow is assumed to be axisymmetric in each meridional blade passage. The impact of the solid blade shapes on airflow is modeled with blade blockage factor and blade body force. The relationships between blade body force and blade inlet Mach number together with attack angle are established with the deviation angle model and loss model. Meanwhile, the effect of the turbulent mixing is also taken into consideration. This developed computational code is then applied to the investigation of a transonic fan rotor and of a four-stage low-speed axial compressor under clean and distorted inlet condition. The predicted performance of both the fan rotor and the four-stage compressor with clean inlet are in line with the experimental results. A quantitative comparison is made between the computational results and the measurement data of the fan rotor with inlet distortion. Additionally, the transfer behavior of inlet distortion in the four-stage compressor is simulated by the model. All results demonstrate the effectiveness and practicability of the model.

This paper includes parametric study and optimization of non-linear ceiling fan blades by combining the techniques of Design of Experiments (DOE), Response Surface Methods (RSM) and Computational Fluid Dynamics (CFD). Specifically, the nonlinear (elliptical) planform shape of ceiling fan blade is investigated in conjunction with blade tip width, root and tip angle of attack. Sixteen cases are designed for three blade ceiling fan using two level full factorial model. The flow field is modeled using Reynolds-Averaged-Navier-Stokes approach. The performance variables used to formulate a multi-objective optimization problem are volumetric flow rate, torque and energy efficiency. Response Surface Method is used to generate the optimized design for non-linear ceiling fan blade profile. The results reveal that the interactions between the design variables play a significant role in determining the performance. It is concluded that the nonlinear forward sweep has a moderate effect on response parameters.

An experimental and analytical study of the tonal trailing-edge noise of a symmetric NACA-0012 aerofoil and of a cambered SD7003 aerofoil has been achieved. It provides a complete experimental database for both aerofoils and improves the understanding of the underlying mechanisms. The analysis stresses the high sensitivity of the tonal noise phenomenon to the flow velocity and the angle of attack. Several regimes of the noise emission are observed depending on the aforementioned parameters. The contributions of the pressure and the suction sides are found to vary with the flow parameters too. A special attention has been paid to the role of the separation bubble in the tonal noise generation. Hot-wire measurements and flow visualization prove that the separation bubble is a necessary condition for the tonal noise production. Moreover, the bubble must be located close enough to the trailing edge. Several tests with small-scale upstream turbulence confirm the existence of the feedback loop. Analytical predictions with a classical trailing-edge noise model show a good agreement with the experimental data; they confirm the cause-to-effect relationship between the wall-pressure fluctuations and the radiated sound. Finally, previously reported works on fans and propellers are shortly re-addressed to show that the tonal noise associated with laminar-boundary-layer instabilities can take place in rotating blade technology.

One-third octave band and narrowband spectra and continuous directivity patterns radiated from an inlet are presented over ranges of fan operating conditions, tunnel velocity, and angle of attack. Tunnel flow markedly reduced the unsteadiness and level of the blade passage tone, revealed the cut-off design feature of the blade passage tone, and exposed a lobular directivity pattern for the second harmonic tone. The full effects of tunnel flow are shown to be complete above a tunnel velocity of 20 meters/second. The acoustic signatures are also shown to be strongly affected by fan rotational speed, fan blade loading, and inlet angle of attack.

Low-speed axial cooling fans are frequently used to manage engine temperature by ensuring that adequate quantities of air pass through heat exchangers, even at low vehicle speeds or in the idle condition. This study aims to provide a better understanding of the unsteady flow behavior around an automotive axial cooling fan with seven blades and its impact on the aerodynamic noise generation. Large Eddy Simulation (LES) near the near-field region and the Ffowcs-Williams and Hawkinbygs (FW-H) method were performed to analyze the flow characteristics around the fan and predict the aerodynamic noise emitted from the fan under a constant rotational speed of 2100 rpm. The simulation results for the velocity distributions and aerodynamic noise were compared with the experimental data measured by single hot-wire probe and in a dead-sound room. The results showed a comparatively good agreement upstream and downstream from the fan and at two different receivers of 0.5 m and 1.0 m. When the fan was rotating, a strong tonal noise numerically existed near the leading edge of the blades at the tip and amounted to 110 dB sound pressure level (SPL) caused by the increasing angles of attack with the increasing radial velocity near the ring, which caused the entire air foil to emit a low-frequency noise. Furthermore, the different SPL decay characteristics of approximately 5 dB in the near-field region and 6 dB in the far-field region were observed each time the distance from the fan doubles. The findings of this research can provide important insights into the design of axial fans with low noise and high performance.

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The inlet distortion arising on a generic fan-in-wing wind-tunnel model is investigated by means of unsteady Reynolds-averaged Navier–Stokes simulations. Flow separation occurs on the inlet lip and generates a separation bubble above the rotor blades. A distortion of the total pressure distribution at the fan inlet significantly influences the blade loading. The strong flow-velocity gradient over the inlet lip induces an increase of the axial-velocity magnitude, resulting in a reduction of incidence angle on the rotor blade. In the bubble-core region, the low axialvelocity magnitude enhances the blade incidence angle and provokes blade tip stall. Steady-state calculations, using an actuator disk approach, are also conducted to identify the key parameters affecting lip boundary-layer separation. The ratio of freestream velocity to fan jet velocity and the inlet-lip radius affect the total pressure distribution bymodifying the location of the flow separation. The angle of attack on the wing has a negligible impact on the inlet distortion. An inlet lip with a large radius at its front part suppresses the lip separation and considerably reduces the total pressure distortion. Injecting a jet over the inlet lip can be a solution to actively control the lip flow.

This paper describes the prediction of broadband self noise from ducted fans. The source mechanism is assumed to be the interaction of the turbulent boundary layer with the trailing edges of the fan blades. The source levels are obtained from the measurements of self noise from isolated blades by Brooks, Pope and Marcolini and these are corrected to give the in duct sound power from a high solidity fan. It has been found that the blade surface pressures are not uncorrelated on each fan blade and corrections must be included for the scattering from multiple trailing edges. A method is introduced for coupling the modes in a circular duct to the modes of a linear cascade so that the sound power is not singular at the mode cut on frequencies. Results show that the in duct sound power scales with the fifth power of the fan speed at low Mach numbers, but this changes to the sixth power or greater at high Mach numbers. The angle of attack of the blade increases the self noise as 2.4 dB per degree and there are significant increases in low frequency noise when blade stall occurs.

*† ‡ Ducted fan performance was calculated using the AMI panel method VSAERO coupled with the ROTOR propeller module. Calculations were performed for a set of experimental data measured on a test model in the NASA Ames facility. The ducted fan model was a generic representation of a class of proposed small UAV systems. Good correlation of duct and rotor thrust and aerodynamic pitching moments was found for all conditions under which the duct lip flow was attached. Empirical extensions to stalled duct lip results can be made for high rotor thrust. I. Introduction new class of unmanned aerial vehicles under development are small ducted fans. These vehicles have no separate lifting surfaces but instead rely on rotor and fan-induced thrust for lift and maneuvering. These UAVs operate primarily at low speeds, high thrust, and high angles of attack. An area of particular concern for these UAVs is translational performance in hover. In this flight condition (nearly 90 degrees angle of attack with respect to the duct thrust axis) a large aerodynamic pitching moment is generated which tends to pitch the vehicle away from the direction of translation. This pitching moment requires additional control authority to overcome and in many cases can severely limit the translational speed of the hovering vehicle. A computer code well suited to the task of calculating these flows is the ROTOR module of the AMI panel method VSAERO. ROTOR computes the coupled effects of the propeller induced flow and the external flow around the duct. The code combines a blade element theory propeller calculation with the VSAERO potential flow solution for arbitrary bodies in subsonic flow. The code takes into account induced effects of the propeller such as asymmetric inlet lip suction and the effects of the exhaust flow in thrust vectoring. Computations for a generic ducted fan UAV compare favorably with test results. The overall lift, drag, and pitching moments developed by the vehicle can be calculated with the VSAERO/ROTOR method for all flight conditions in which attached flow is maintained around and through the duct inlet. This includes the high angle of attack and high thrust conditions (representing crosswinds in hover) which are of particular concern to this class of vehicle. While the very high duct angles of attack would initially seem to preclude the successful use of a potential flow method, the high duct thrust and resulting high mass flows through the duct maintain attached flow through the duct. The resulting flow field can be successfully calculated with this method. . Empirical correlations of duct stall can be used to provide limits of attached flow behavior and guidelines for estimates of aerodynamic forces and moments beyond duct stall.

The objective of this work was to develop and verify a data acquisition and reduction conditional sampling technique suitable for the laser velocimeter which would allow multicomponent velocity and turbulence intensity measurements near and between the rotating propeller or fan blades A relatively simple experiment was set up to measure the flowfield of a two bladed propeller operating at static (nonflight) conditions to verify these procedures The program consisted of acquiring time averaged, mean and ensemble averaged, blade to blade distributions of velocity and turbulence intensity data for all three velocity components Separated and reverse flow regions were located on a rotating static propeller The radial distribution of the static propeller section angle of attack was also measured during rotation Blade to blade distributions revealed that a negative prewhirl exists in front of the propeller disk Behind the propeller a distinct distortion of the flowfield due to the presence of the propeller blade wake was observed

The main objective of this paper consists of the computation of the aerodynamic performances of symmetrical blade contours of fully reversible axial fans by Numerical (CFD) methods, developing by a public literature survey, methodology for the design of reversible axial fans and analysis of the designed fan with CFD methods. The aerodynamic shows of the blade cascades are evaluated using FLUENT 6.0 software for different boundary conditions, strengths and angles called Angle of Attack(AoA) cascade also performing for varying speeds. The consequences of these computations are embedded into the industrialized methodology. Which is designed with the developed methodology, is done with Numerical methods.

In this study, the wake characteristics of an arc blade were measured by the wind tunnel experiment; the characteristics were defined as the width of the wake, diameter of the vortex, ratio of the vortex scale, and the local lift. The influence of the angle of attack on the aerodynamic noise of the blade was quantitatively predicted by using these characteristics. It was clarified experimentally that the sound pressure of the aerodynamic noise becomes small since the gradient of the differential of the lift fluctuation was reduced according to the increase of the angle of attack. The wake characteristics were applied to the prediction of the broadband noise generated from a multiblade fan; the fan noise level distribution was estimated with high accuracy to be in the range from 1000-3000 Hz and was used to analyze the broadband noise of the fan. From the analysis of the fan noise level, it was found that the difference in the relative velocity caused by the biased internal flow was related to the noise levels.

Underground mining safety relies heavily on ventilation, which is energy and maintenance intensive. An optimization method for an axial-flow Chinook ventilation fan, analyzing parameters like angle of attack, tip clearance, rotation speed, hub-to-tip ratio, and rotor blade count using Design of Experiments (DOE) and regression is proposed. The numerical solutions are confirmed with experimental data. Considering a Mach number of 0.4, compressible flow conditions are analyzed using a two-equation turbulence model. During stall, fan efficiency drops to 47 %. High fatigue probability is observed at the blade-root intersection in stall conditions. The optimization pinpoints several operational configurations that meet the required performance while preserving the fan's structure. A particular off-design optimal point indicates that reducing the blade count and decreasing the tip-clearance lead to an average performance improvement of 9 %, with significant benefits in noise, cost, weight, and energy consumption. The numerical forecasts demonstrate precision with an average discrepancy of less than 5 %.

Ceiling fans are the most used resource for providing indoor thermal comfort in hot climates because of factors like low cost, easy availability and less electric consumption compared to air conditioning units. The fan industry of Pakistan is well-renowned on the national scale. In this paper, the features of the flow field generated by the ceiling fans under different geometric shapes are discussed. Specifically, the effect of forward elliptic sweep angle is studied on the performance of ceiling fans. Other geometric variables considered are tip width, root and tip angle of attack. The response variable considered for parametric analysis as well as optimization studies is the rated air delivery. The benchmark design is the reference blade being sold in market. By applying Design of Experiment (DOE), sixteen experiments are designed for new blades. These new blade designs are simulated through Reynolds-Averaged-Navier-Stokes (RANS) commercial flow solver. The computational model is developed around the same experimental facility and validated with experimental data. Subsequently, statistical tools are used to study the effect of individual parameters as well as their interactions. Finally, Response Surface Methodology (RSM) is used to find the optimal solution in the design space.

Actuator-disk models (ADMs) use blade element theory to numerically simulate the flow field induced by axial fans. These models give a fair approximation at near design flow rates, but are of poor accuracy at low flow rates. Therefore, the lift/drag (LD) characteristics of two-dimensional (2D) sections along the span of an air-cooled heat exchanger (ACHE) axial fan are numerically investigated, with the future prospect of improving ADMs at these flow conditions. It is found that the blade sectional LD characteristics are similar in shape, but offset from the 2D LD characteristics of the reference airfoil (NASA LS 413 profile) at small angles of attack (αatt&lt;5deg). A deviation between these characteristics is observed at higher angles of attack. The blade sectional lift coefficients for αatt&gt;5deg always remain lower compared to the maximum lift coefficient of the reference airfoil. Conversely, the blade sectional drag coefficients are always higher compared to that of the reference airfoil for αatt&gt;5deg.

A study is made of the various mechanisms which generate broadband noise on a range of rotors The sources considered are load fluctuations due to inflow turbulence, due to turbulent boundary layers passing the blades' trailing edges, and due to tip vortex formation Vortex shedding noises due to laminar boundary layers and blunt trailing edges are not considered as they can be prevented in most cases Various prediction methods have been reviewed and extended in some cases An extensive search was made of existing experiments and calculations based on the various prediction methods were made This study shows that present analyses are adequate to predict the spectra from a wide variety of experiments on fans, full scale and model-scale helicopter rotors, wind turbines, and propellers to within about 5 to 10 dB Better knowledge of the inflow turbulence improves the accuracy of the predictions The results of this study indicate that inflow turbulence noise depends strongly on ambient conditions and dominates at low frequencies Trailing edge noise and tip vortex noise are important at higher frequencies if inflow turbulence is weak Boundary layer trailing edge noise is important especially in the presence of large rotors; it increases slowly with angle of attack but not as rapidly as tip vortex noise, which can be important at high angles of attack for wide chord, square edge tips