Dissertations / Theses on the topic 'Axial fan noise'

This work was concerned with the aerodynamic and acoustic performance of small axial flow refrigerator fans. Relevant literature focusing on the principles of fan noise generation and fan system elements that contribute to noise generation was identified and discussed. A plenum chamber test rig was designed and constructed following ISO 10302-1. A range of 200 mm diameter pressed aluminium Air-Drive fans, commonly used in commercial refrigerator systems, were evaluated using the test rig. It was found that the performance of these fans was highly dependent upon the impedance of the system in which they are installed. Indications of rotating stall under high load were observed and shown to significantly increase the noise output of the fan without greatly affecting the air moving capability. A series of novel colour map plots are presented, which allow for a visual interpretation of fan performance over a wide range of operating conditions. A fanpack developed by Wellington Drive Technologies Ltd was evaluated. This fanpack was found to generate significant tonal noise. The design of the fanpack was evaluated and improvements are suggested. Prototype fans were developed from the fanpack based on promising concepts presented in the literature. The performance of four prototype fans was evaluated. The results were disappointing, but proof of concept was demonstrated.

A new active-passive approach for the control of noise radiated from a small axial fan was investigated. The approach involved the installation of an axial fan into a short duct with both passive and active noise control functions. First, a systematic methodology for the analytical modeling of finite-length ducts with multiple discontinuities was formulated. The procedure involved the modeling of a duct as a collection of simple duct sections, which were interconnected at multiple junctions. Analytical studies have shown that a short lined duct provides passive noise reduction effects through the mass-loading effect of the duct air volume at low frequencies and the sound absorption by a passive liner at high frequencies. It was also shown that active control can provide further noise attenuations at low-to-mid frequencies, thereby enhancing the overall noise control performance. Two alternate designs of active-passive noise control fan duct were considered. One was a simple non- segmented duct with a 2x2 active control and the other was an internally segmented duct with an 8x8 active control. It was indicated that the latter design possesses a significantly higher global noise control potential than the former with respect to both bandwidth and attenuation level. This was attributed to the reduction of the unwanted pressure contributions from the duct cross modes through the high frequency shifting of the associated cut-on frequencies. The experimental validation of the noise control approach was also carried out. An active-passive noise control fan duct incorporating the segmented duct design with 8x8 active control was constructed in conjunction with a hybrid feedforward-feedback control system. Experimental results have shown significant reductions in the total fan noise power associated with the first four BPF tones by the feedforward control and the broadband fan noise power by the feedback control. The overall active-passive noise control characteristics were observed to be in accordance with the analytical results.
Ph. D.

Recent experimental achievements in active noise control (ANC) for cooling fans have used near-field error sensors whose locations are determined according to a theoretical condition of minimized sound power. A theoretical point source model, based on the condition previously stated, reveals the location of near-field pressure nulls that may be used to optimize error sensor placement. The actual locations of these near-field pressure nulls for both an axial cooling fan and a monopole loudspeaker were measured over a two-dimensional grid with a linear array of microphones. The achieved global attenuation for each case is measured over a hemisphere located in the acoustic far field of the ANC system. The experimental results are compared to the theoretical pressure null locations in order to determine the efficacy of the point source model. The results closely matched the point source model with a loudspeaker as the primary source, and the sound power reduction was greatly reduced when error sensors were placed in non-ideal locations. A weakness of the current near-field modeling process is that a point monopole source is used to characterize the acoustic noise from an axial cooling fan, which may have multipole characteristics. A more complete characterization of fan noise may be obtained using a procedure based on the work of Martin and Roure [J. Sound Vib. 201 (5), 577--593 (1997)]. Pressure values are obtained over a hemisphere in the far field of a primary source and the contributions from point source distributions up to the second order, centered at the primary source, may be calculated using a multipole expansion. The source information is then used in the aforementioned theoretical near-field calculation of pressure. The error sensors are positioned using the complete fan characterization. The global far-field attenuation for the multipole expansion model of fan noise is compared to that of previous experiments. Results show that the multipole expansion model yields a more accurate representation the near field, but is not successful in achieving greater sound power reductions in the far field.

ENGLISH ABSTRACT: A design routine was derived for designing a series of rotor-only axial flow fans. The routine was applied by designing two different series of axial flow fans. The first design was for a general application rotor-only axial flow fan. This fan series was designed, built and tested in co-operation with Howden Air Industries for both research and commercial purposes. The second design was for a low-noise fan series, which was designed, built and tested by the University of Stellenbosch for research purposes only. The design theory used the principle of blade cropping, meaning that one blade was designed to fit all the different fan sizes. The fan series was designed for diameters ranging from 3 15 mm to 1000 mm. The fan rotors were designed to conform to a velocity profile of minimum exit kinetic flux. The general application fan design was concentrated around the popular fan diameter sizes of 500 rnm, 560 mm and 630 mm and a rotor speed of 1440 rpm, using a commercially available fan series as reference. The low-noise fan design concentrated on one fan size only, namely 630 mm, while also making use of the principle of forward blade sweep. The remaining fan design principles stayed the same as for the general application fan design. The F-series airfoils were used as blade sections for both fan designs. Both fan series were tested for fan noise and performance in accordance with the BS 848 Standards part 1 (1980) and 2 (1985). A selection of fan diameter sizes was tested for the general application fan to verify its perfo!"mance over a range of fan sizes. This indicated a fan series with a wide range of efficient operation, including excellent noise characteristics. A 630 mm diameter fan was used to test the low-noise fan series. It showed both high efficiency and low noise characteristics. The reduction in fan noise achieved with the low-noise fan does not justi1)' the amount of work and costs involved in the designing process, compared to the general application fan.
AFRIKAANSE OPSOMMING: 'n Ontwerpsroetine vir die ontwerp van 'n reeks enkelrotor aksiaalwaaiers is ontwikkel. Die roetine is toegepas deur twee verskillende reekse aksiaalwaaiers te ontwerp. Die eerste ontwerp was vir 'n algemene toepassings enkelrotor aksiaalwaaier. Die waaierreeks is ontwerp, gebou en getoets in samewerking met Howden Air Industries vir beide navorsings - en kommersieIe doeleindes. Die tweede ontwerp was vir 'n lae geraas waaierreeks. Die reeks is ontwerp, gebou en getoets deur die Universiteit van Stellenbosch vir navorsingsdoeleindes. Die onwerpsteorie het gebruik gemaak van die beginsel van lemverkorting, waardeur een lem ontwerp is om op al die groottes waaierdeursnee te pas. Die waaierreekse is ontwerp vir waaierdeursnee tussen 315 mm en 1000 mm. Die rotors is ontwerp om 'n uitlaatsneIheidsprofiel te gee wat 'n minimum verlies in kinetiese energie toelaat. Die algemene toepassings waaierontwerp het gekonsentreer rondom die gewilde waaierdeursnee van 500 mm, 560 en 630 mm. Dit is ontwerp vir 'n rotorspoed van 1440 met 'n kommersieel beskikbare waaierreeks wat as verwysing gebruik is. Die lae geraas waaierreeks het op slegs een waaiergrootte gekonsentreer, naamlik 630 mm. Die lae geraas waaierreeks is ook ontwerp met vorentoe gekurfde lemme. Die res van die ontwerpsbeginsels was dieseIfde as vir die algemene toepassings waaierreeks. Die F-reeks vleuelprofiele is gebruik vir die lemseksies van beide waaierreekse. Beide waaiereekse is getoets vir waaiergeraas en -effektiwiteit deur gebruik te maak van die BS 848 Standaarde deel 1 (] 980) en 2 (] 985). 'n Verskeidenheid van waaierdeursnee van die algemene toepassings waaierreeks is getoets om die waaier se vertoning oor 'n gebied van waaiergroottes te bepaal. Die resuItaat was 'n waaierreeks met 'n wye gebied van effektiewe werking, asook uitstekende geraaseienskappe. 'n 630 mm Deursnee waaier is gebruik om die lae geraas waaier te toets. Die toetse het 'n waaier getoon wat beide hoe effektiwiteit en lae geraaseienskappe het. Die afname in waaiergeraas wat verkry is met die lae geraas waaier, in vergelyking met die algemene toepassings waaier, regverdig egter rue die werk en kostes verbonde aan die ontwerp van die waaierreeks nie.

Vehicle electrification plays a significant role in the effort to reduce the environmental impact of the automotive industry. Scania is one of the leading manufacturers ofheavy vehicles which is currently moving towards a sustainable transport system by manufacturing a new generation of heavy vehicles powered by batteries. Oneof the major concerns with these vehicles is related to the noise generated by the electric axial fans used in the cooling system. This project was conducted with thepurpose of investigating the factors that positively affect both noise and performance in the electric fans. Based on two different blade design methods and several noisecontrol techniques, 11 fan models were developed. The fan models created with design method 1 are equipped with cambered-plate blades, while the models madewith design method 2 consist of airfoil-shaped blades. Moreover, the performance of these models was analyzed by using theoretical methods and Computational FluidDynamics (CFD). In addition, two empirical approaches were used to estimate the acoustic energy emitted by the fan models. Furthermore, the developed modelswere compared with two commercially available fans. It was found that both design methods provide similar performance in low pressure differences. On the other hand,the efficiency and acoustic energy are influenced by the choice of the noise control methods.
Fordonselektrifiering har en väsentlig roll i arbetet med att minska bilindustrins miljöpåverkan. Scania är en av de ledande tillverkarna av tunga fordon som för närvarandegår mot ett hållbart transportsystem, genom att tillverka en ny generation tunga fordon drivna med batterier. Ett stort bekymmer med dessa fordon är relaterattill det ljud som genereras av de elektriska axialfläktarna som används i kylsystemet. Detta projekt genomfördes i syfte till att undersöka de faktorer som positivtpåverkar både buller och prestanda hos de elektriska fläktarna. Baserat på två olika bladdesignmetoder och flera brusstyrningstekniker, utvecklades 11 fläktmodeller.Fläktmodellerna som är utformade med konstruktionsmetod 1 är utrustade med krökformade plattor, medan modellerna som skapades med designmetod 2 bestårav vingprofil blad. Dessutom analyserades prestandan för dessa modeller med användning av teoretiska metoder och strömningsmekaniska beräkningar. Ytterligaretvå empiriska tillvägagångssätt användes för att uppskatta den akustiska energin som släppts ut av fläktmodellerna. Utöver det jämfördes de utvecklade modellernamed två kommersiellt tillgängliga fläktar. Detta visade att båda konstruktionsmetoderna resulterar i liknande prestanda vid lågtrycksskillnader, däremot påverkasverkningsgraden och den akustiska energin av valet av brusstyrningsmetoder.

Multiple fans are sometimes used in an array configuration to cool various types of electronic equipment. In addition to adding another noise source, using two fans with closely spaced blade passage frequencies (BPF) can create an annoying beat frequency. A two fan array with each fan having a different BPF was considered. The fans were theoretically modeled at the BPF and first harmonics. Each fan has two acoustic paths to the far field. Thus, each fan was modeled as a two source array. The first control configuration consisted of one control filter using six control sources and six error sensors in a fully coupled control system designed to control both fans simultaneously. The second configuration used two independent controllers with three control sources and three error sensors, one controller per fan. Experimentally, the averaged narrow band reduction of the BPFs and the second harmonic of the two independent controllers were 15.6 and 7.4 dB respectively, compared to a reduction of 14.4 and 5.7 dB at the two frequencies using a single control loop. The results suggest that independent controllers perform better than the single control loop for the fan array studied. Optimization of active noise control systems has increased performance but sometimes with decreased robustness. Two control source configurations for the sound power reduction of a simple source were analyzed by modeling the control systems. The two control source configurations were four symmetric control sources surrounding the noise source and an optimized linear array of four control sources. Simulation results show the linear array control source configuration is more sensitive to microphone placement errors, with a 20-33 dB reduction in attenuation for a microphone placement error of 2 mm compared to a 0.8 dB drop in attenuation for the symmetric case. The linear array configuration was found to be more sensitive to the microphone placement errors compared to the symmetric configuration. A 2.5 mm change in one microphone position causes an average of 6 dB loss in attenuation for the linear array configuration compared to a 0.6 dB loss for the symmetric configuration.

Le bruit tonal d’interaction rotor-stator, généré par l’impact des sillages issus des pales d’un rotorsur la grille d’aubes d’un stator redresseur, contribue de manière déterminante au bruit d’origineaérodynamique des turbomachines axiales carénées, qui équipent une large part des systèmes de propulsionaéronautique et de conditionnement d’air. La prédiction du bruit par l’utilisation de simulationsnumériques demeure onéreuse, notamment dans les premières phases de conception lorsque de nombreusesconfigurations doivent être testées. Dans cette optique, l’approche analytique choisie dans cettethèse apporte une alternative tout à fait appropriée. Les modèles analytiques basés sur une fonctionde réponse aéroacoustique de profil isolé ne permettent pas de reproduire l’effet de grille engendrépar le nombre important d’aubes de stator. Inversement, de fortes approximations sont nécessairespour décliner les fonctions de réponse de grilles d’aubes existantes dans des configurations tridimensionnelles.Le formalisme proposé, basé sur la méthode de raccordement modal, permet d’introduiresimplement l’effet de grille dans une géométrie annulaire d’étage rotor-stator. Un modèle de réponse degrille rectilinéaire bidimensionnel est tout d’abord présenté pour la transmission d’ondes acoustiques àtravers le stator ainsi que pour la génération de bruit par l’impact de rafales hydrodynamiques. Dansce cadre, une analyse linéaire et non visqueuse est considérée, pour laquelle les modes acoustique ettourbillonnaire d’un gaz sont couplés par le biais des frontières rigides. Les perturbations de vitessesliées aux sillages sont modélisées comme des rafales convectées. Leur impact sur la grille de statorgénère des ondes acoustiques se propageant en amont, en aval ainsi que dans les espaces inter-aubesdu stator, vu comme un réseau périodique de guides d’ondes. Les sections de bords d’attaque et defuite des aubes sont considérées comme des interfaces sur lesquelles la continuité des fluctuations depression, de vitesse axiale et de vorticité est vérifiée. Un système d’équations est ainsi obtenu, puisrésolu par des projections sur les bases modales du conduit et des inversions matricielles. Le champacoustique rayonné est ainsi déterminé uniformément dans tout le domaine. Les résultats issus de cesmodélisations sont comparés à ceux des fonctions de réponse de grilles d’aubes rectilinéaires issues dela littérature, montrant un très bon accord avec les modèles basés sur la technique de Wiener-Hopf. Leformalisme est par la suite étendu aux grilles annulaires par l’ajout de fonctions de Bessel comme fonctionsde forme radiale exprimant les effets tridimensionnels. Finalement, une procédure est présentéepour rendre compte de l’hétérogénéité des aubes de stator, caractéristique des nouvelles architecturesde turbomachines. Cette méthodologie est basée sur l’emploi conjoint du principe du dipôle de bordd’attaque et de la fonction de réponse aéracoustique de la grille de stator à l’aide de la technique deraccordement modal. Le principe de dipôle de bord identifie le chargement instationnaire des aubesinduit par l’impact de rafales hydrodynamiques, calculé par le formalisme d’Amiet, avec la trace duchamp de pression acoustique produit par un dipôle placé au voisinage du bord de l’aube. Les prédictionsissues de ce modèle, appliqué dans un cadre bidimensionnel, sont ensuite comparées à des mesuresobtenues pendant la campagne d’essais du projet SEMAFOR
The rotor-stator wake-interaction tonal noise, generated by the impingement of rotor wakes onoutlet guide vanes, plays a crucial role in the aerodynamic noise of axial-flow ducted fan stages. Thelatter are widely used in most aeronautic propulsion and air-conditioning systems. The noise predictionby means of numerical simulations remains expensive, especially at the preliminary design stage whennumerous configurations must be tested. In this respect, the analytical approach chosen in this thesisprovides a well suited alternative. The analytical modeling based on an isolated-airfoil response functioncan not reproduce the cascade effect introduced by the large number of stator vanes. Conversely, drasticapproximations are required to extend the current cascade response functions to three-dimensionalconfigurations. The proposed modeling based on the mode-matching technique simply introduces thecascade effect in an annular rotor-stator stage. A rectilinear cascade response function is firstly presentedto account for the acoustic transmission through the stator along with the wake-interaction noise.In this context, a linearized and non-viscous analysis is carried out, in which the acoustic and vorticalmodes of a gas are coupled at rigid physical boundaries. The velocity perturbations issued from thewakes are written as a sum of convected gusts. Their impingement on the cascade of vanes generatesacoustic waves propagating upstream, downstream of the cascade, as well as inside the inter-vane channelsof the stator, seen as a periodic array of bifurcated waveguides. The duct cross sections at theleading-edge and the trailing-edge of the vanes are seen as interfaces on which the continuity of thefluctuating pressure, axial velocity and vorticity is fulfilled. A system of linear equations is obtained,then solved by means of modal projections and matrix inversions. The acoustic field is then uniformlycalculated in the whole domain. Comparisons with rectilinear cascade response functions show a verygood agreement with predictions based on the Wiener-Hopf technique. The configuration of an annularcascade is addressed by introducing the Bessel functions as radial shape functions, expressing threedimensionaleffects. Finally, a procedure is presented to account for the heterogeneity of the statorvanes, typical of modern fan architectures. This approach is based on the combinaison of the leadingedgedipole principle and the cascade response function derived from the mode-matching technique.The edge-dipole principle identifies Amiet’s solution for the unsteady loading and the radiation of adipole approached very close to the edge of a half plane. The predictions provided by this modeling,applied in a two-dimensional configuration, are finaly compared to measurements performed in the testcampaign of the SEMAFOR project

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This work consists in an analysis of the noise level generated by axial flow fans composed of centrifugal rotors with radial blades, where the main objective is the development and validation of a methodology for the prediction of the aerodynamic noise generated by these fans. The proposed methodology was developed based on works available in the literature, in which the emitted sound power level is calculated through analytical equations that use experimentally calibrated parameters and variables related to the fan operating point, such as volume flow, pressure, absorbed power, peripheral velocity, among others. The fan aerodynamic variables were obtained with the aid of CFD techniques, which require a validation process. This validation process is accomplished by means of the comparison between the CFD and experimental results. The methodology validation is achieved by the comparison between the predicted and the experimental results of the sound pressure levels and the fan aerodynamic variables. All experiments involved in the present work were carried out following the procedures and criteria established by technical standards. The main acoustic resonance modes of the fan were also determined by means of the numerical simulations and validated through experimental sound measurement techniques of the type Waterfall.
Este trabalho consiste em uma análise do nível de ruído gerado por ventiladores de fluxo axial composto por rotores centrífugos de pás radiais, onde o principal objetivo é o desenvolvimento e a validação de uma metodologia para predição do nível de ruído aerodinâmico gerado por tais ventiladores. O desenvolvimento do método proposto é fundamentado em trabalhos disponíveis na literatura, onde o nível de potência sonora emitida por ventiladores é calculado através de equações analíticas que usam parâmetros calibrados experimentalmente e variáveis relacionadas ao ponto de operação do ventilador, como vazão, pressão, potência absorvida, velocidade periférica, entre outros. As variáveis aerodinâmicas do ventilador foram obtidas com o auxílio de técnicas de CFD, as quais necessitam de um processo de validação. Esse processo é executado por meio da comparação entre os resultados de CFD e experimentais. A validação da metodologia é realizada pela comparação entre os resultados preditos e os experimentais dos níveis de pressão sonora e das variáveis aerodinâmicas do ventilador. Todos os experimentos envolvidos no presente trabalho foram executados conforme procedimentos e critérios estabelecidos por normas técnicas. Os principais modos de ressonância acústica do ventilador também foram determinados por meio de simulações numéricas e validadas através de técnicas de medição sonora experimental do tipo Waterfall.

碩士
國立屏東科技大學
機械工程系所
98
This text discuss Optimum design of vane axial fan and noise analysis. The vane axial fan than normal axial fan axial fan can generate a better flow field,and assisted by static blades, can spread rotor blades air emissions from its centralized, its better performance. Vane axial fan because of the effect of air concentration, in the same space and the environment will not display multiple sets of interference in each other's problems. Therefore, vane axial fan used in servers, computer rooms, CNC equipment. Such circumstances may have a greater heat problem, to avoid thermal effects of electronic components function, then according to become damaged, it is now more and more technology vendors for equipment needs, and then use the vane axial fan. Experiment will use the Taguchi method for the frame and blades, respectively, the optimum operation, observe the performance parameters corresponding to the trend and noise analysis. Supplemented by fluid simulation software to verify the experimental data with each other. Last is the fan part of the use of finite element analysis, do the structural strength of the blades.

碩士
國立臺灣科技大學
機械工程系
87
This thesis is aimed at how to improve the performance and noise of a P.C. cooling fan. First of all, a basic geometry of an axial-flow fan is generated by the theoretical analysis; then, the corresponding experiments are executed the performance and noise characteristics in the AMCA test chamber and semi-anechoic room based on AMCA-210-85 and ISO9614-1 standards respectively. Later, several modifications on the fan configuration such as attaching second-flow device, roughen blade surface, and adding groove on fan frame are introduced to verify the corresponding influences on fan performance and noise. In summary, the experimental results show that the attachment of second-flow device can enhance the fan static pressure by 8.2% in the low to middle-flow- rate ranges; besides, 3 to 6 dBA noise reduction on the narrow-band frequency is obtained. Moreover, under the similar noise level, 5 and 5.3 percentages of fan static-pressure gains are demonstrated in the middle flow rate range for the roughen blade surface and adding groove on fan frame, respectively.

碩士
國立臺北科技大學
能源與冷凍空調工程系碩士班
105
With the increase of power consumption and heat generation, using CFD software can greatly reduce the time and cost of making the fan entity and measuring the fan curve. Accuracy of the ANSYS Fluent simulation was checked with experiment on the basis of the AMCA-210-99 standard at first. The average error is less than 10%, then, using the Taguchi method to optimize the fan efficiency and reduce noise. Four factors were studied in this thesis, i.e. fixed stagger angle, free stagger angle, fan blade height and fan cross section shape. Influences of different fan factors on the performance, volume flow rate, pressure, torque, fan efficiency and noise were examined. Totally, 9 sets of simulations were obtained .The data were analyzed through Signal-to-Noise Ratio method, by using MINITAB software, the best factor level of two quality characteristics were obtained. The results show that although volume flow rate increased slightly, fan torque declined 24%, therefore fan efficiency increases from 22.45% to 30.07%. Noise declined from 54.439dB to 53.214dB.

碩士
國立虎尾科技大學
機械與機電工程研究所
100
During the design and manufacturing process of a fan, various shapes, size of the blade and installing angle are designed for different requests. Reaction to the rapid market demands, the CAD and CAE analyses are applied to analyze the fluid flow field and noise distribution of a fan for different parameters to satisfy the required fan performance and noise level. In this study, numerical investigation of fluid flow and noise distribution of an axial-flow fan for air-conditioning is conducted by using FLUENT computational fluid dynamics software that MRF(Multiple Reference Frame) is adopted to describe the rotation parts as well as static parts of a fan and finite volume method(FVM) is applied to solve the mass, momentum equations. The results show that the 1st set with blade diameter 580mm, installing angle 40 degree, rotating between 900 to 1500 rpm, or the 2nd set with blade diameter 390mm, installing angle 38 or 40 degree, rotating between 1200 to 1500rpm, satisfy our design requirements.

碩士
國立臺北科技大學
車輛工程系所
95
Using acoustical analysis techniques investigate cross flow fan arising from the operation strident sound issues. This research change axial configurative tongue design with aperture or comb shaped ; and adopt laboratory tests to verify its feasibility. The results be proved these different changes can decrease cross-flow fan BPF peak, in particular reduce 8 dB (A) noise effects at specific rpm. Generally, the cross flow fan operating noise totally about 55 dB(A), but in the midnight when prominent frequency noise has become extremely annoying. This research attempted to different axial configurative tongue designed to improve penetrating single frequency noise of cross-flow fan. And further analyze acoustical parameters to fine the best tongue with impeller RSA（Rotor-Skewed Angle）mixed . Through CFD (Computational Fluid Dynamics) analysis software Fluent 6.2 forecast its feasibility and effectiveness. The acoustic analysis results of axial configurative tongue design with aperture or comb shaped can reduce the BPF peak effects. Therefore we can not only receive better sound quality on the experiments, but also get a similar effect in fluent 6.2 simulations.

The aim of this investigation is the aeroacoustic analysis of the boundary layer separation noise and trailing edge noise in a heat pump axial fan, using Computational Fluid Dynamics (CFD), Fluid Fluid Structure Interaction (FSI) and Computational Aeroacoustics (CAA). The Broadband Noise Source (BNS) model and Transition SST turbulence model, implemented in Fluent 19.0, were used to study the boundary layer noise component of the three noise reduction features in steady-state and transient simulations. The objectives of this study were divided into two main parts: the analysis and optimization of golf ball dimples to control the the boundary layer separation on fan blade and the study regarding the application of two features from the "silent" flight of the owl on the fan, the finlets and the flexible trailing edge. The parametric optimization on dimples showed a 15,1% shift in boundary layer separation. This optimized pattern when applied to the suction side of the fan blade shifting the boundary layer separation which promotes the inhibition of the vortex generated at the junction of the blade with the hub resulting in a reduction of up to 0,8 dB under normal fan operating conditions. It was also found that dimples have a greater influence on operating conditions under an airflow less than 1500 m3/h, showing a shift in the stall resulting in an increase of the fan efficiency by 1,9% and a decrease in the boundary layer noise of 2,9 dB. On the second part of the work it was found that a fan with finlets presented a reduction of 0,3 dB at 300 rpm, although the results showed an increase in noise and a decrease in efficiency for higher rpm than those for which the finlets were optimized. The study of an flexible trailing edge showed a decrease in the thickness of the turbulence generated by the boundary layer. This, due to the downward movement of the flexible trailing edge that decreases the pressure mismatch between the suction surface and the pressure surface and the decrease of the angle of attack caused by its upward movement. Experimental measurements of an dimpled fan prototype, conducted in a hemi-anechoic chamber showed noise improvements in the order of 0,5 dB(A), the results suggested that for lower velocities than 380 rpm an increase in the fan efficiency is expected. Lastly, an attempt was made to induce stall in the fan through the obstruction of the heat pump evaporator. This investigation identified that for an airflow of 1700 m3/h at 535 rpm the original fan enters in a light stall condition while the dimpled fan prototype maintains its normal operating conditions, resulting in a reduction of 0,9 dB(A).
O objetivo deste trabalho de investigação consistiu na análise do ruído aeroacústico emitido pelo ventilador aplicado às unidades exteriores das bombas de calor, recorrendo a Computational Fluid Dynamics (CFD), Fluid Fluid Structure Interaction (FSI) e Computational Aeroacoustics (CAA). O modelo acústico Broadband Noise Source (BNS) e o modelo de turbulência Transition SST, implementados no código comercial Fluent 19.0 foram utilizados para avaliar diferentes técnicas de redução do ruído emitido pela separação da camada limite e pelo bordo de fuga. Os objetivos deste estudo estão divididos em duas componentes: a análise e otimização de cavidades inspiradas nas bolas de golf para o atraso da separação da camada limite na pá do ventilador e o estudo da implementação de duas características do voo "silencioso" das corujas no ventilador, o bordo de fuga alhetado e o bordo de fuga flexível. Os resultados da otimização paramétrica das cavidades das bolas de golf mostram um atraso na separação da camada limite de 15,1%. Este padrão otimizado quando aplicado no lado de sucção da pá do ventilador atrasa a separação da camada limite o que promove a inibição do vortex gerado entre a pá e o centro do ventilador resultando numa redução de até 0,8 dB em condições normais de funcionamento do ventilador. As cavidades das bolas de golf mostram ter uma maior influência para condições de operação com um fluxo de ar inferior a 1500 m3/h, mostrando atrasar o fenômeno de stall, aumentado a eficiência do ventilador em 1,9% e diminuíndo o ruído aerodinâmico em 2,9 dB em comparação com o modelo original. Na segunda parte da tese foi descoberto que um bordo de fuga alhetado revela uma redução de ruído de 0,3 dB a 300 rotações por minuto, sendo que se verifica perda de eficiência e aumento do ruído do ventilador para rotações por minuto superiores aos quais as alhetas foram geometricamente otimizadas. O estudo da utilização de um bordo de fuga flexível mostrou a diminuição da espessura da turbulência gerada pela camada limite através do movimento descende do bordo de fuga flexível que diminui a diferença de pressão entre a superfície de sucção e a superfície pressão e a diminuição do ângulo de ataque com o seu movimento ascendente. Medições experimentais realizados numa câmara semi-anecóica do protótipo do ventilador com cavidades inspiradas nas bolas de golf mostraram melhorias na ordem de 0,5 dB(A) para diferentes rotações por minuto e sugerem um aumento da eficiência para rotações por minuto inferiores a 380. Por fim foi feita a tentativa de induzir um escoamento totalmente separado no ventilador através da obstrução do evaporador da bomba de calor, este estudo identificou que que para um fluxo de ar de 1700 m3/h a 535 rotações por minuto o ventilador original entra em condição de separação total sendo que o protótipo do ventilador com cavidades inspiradas nas bolas de golf mantem condições de funcionamento normais, resultando numa redução de 0,9 dB(A).
Mestrado em Engenharia Mecânica

The aim of this investigation is the aeroacoustic noise analysis of two fan models with different sizes used within two heat pump units, using Computational Fluid Dynamics (CFD) and Computational Aeroacoustics (CAA). The Broadband Noise Source (BNS) model and Transition SST turbulence model, implemented in Fluent 19.0, were used to detect the boundary layer noise component of the case studies in steady-state simulations. The targets of this study were divided in three main parts: analysis of the relation between diameter and tip speed and aeroacoustic noise, the motor cap’s influence on boundary layer noise and the analysis of serrated trailing edges and fans with golf-ball dimples. Results indicate a potential of 3,3 and 4 dB aerodynamic noise improvement at low and high speed flow requirements, respectively, using the bigger fan in the small-chassis, due to the lower speed needed to maintain the same airflow rate. It was found that the motor cap influences downstream airflow and reduces reverse flow. Although influencing the operating point of the fans, using the motor cap shows 0,4 and 0,8 dB improvement potentials for one of the fan models at the aforementioned speed modes, after adjustments for required airflow rates. Lastly, it was discovered that adding dimples to regions of the fan’s surface with a bias towards flow separation can help prevent the phenomenon and reduce turbulent kinetic energy in the near airflow, improving boundary layer noise. This becomes more evident in near-stall/stall operating conditions. The trailing edges didn’t show considerable improvements for the fan model they were added to. Experimental measurements of the three re-scaled 3D printed fan models, conducted in an enthalpic tunnel and a hemi-anechoic chamber, showed noise improvement potentials in the order of 3,7 and 5,3 dB(A) at 350 rpm for the fans with dimples and serrated edges, but new measurements need to be conducted with equal printing quality on all models to confirm the results
O objetivo deste trabalho de investigação consistiu na análise do ruído aero- acústico emitido por dois ventiladores de diâmetros diferentes aplicados em duas unidades exteriores de bombas de calor, recorrendo a Computational Fluid Dynamics (CFD) e Computational Aeroacoustics (CAA). O modelo acústico Broadband Noise Source (BNS) e o modelo de turbulência Transition SST, implementados no código comerical Fluent 19.0, foram utilizados para detetar o ruído da camada limite dos diversos casos de estudo, utilizando simulações em regime permanente. Os objetivos do estudo estão divididos em três componentes: a análise da relação entre o diâmetro e a velocidade de ponta com o ruído aeroacústico, o estudo da influência do disco do motor na acústica da camada limite e a análise de arestas serradas e ventiladores com cavidades inspiradas nas bolas de Golf. Os resultados indicam um potential para redução do ruído aerodinâmico de 3,3 e 4 dB no modo de baixa e alta velocidade, respetivamente, utilizando o ventilador maior no chassis mais pequeno, uma vez que requer velocidades mais baixas para atingir o mesmo caudal de ar. Foi descoberto que o disco do motor influencia a distribuição do caudal à saída do ventilador e que previne o fluxo inverso de ar. Apesar de influenciar os pontos de operação do ventilador, utilizar o disco demonstra um potencial de redução de ruído de 0,4 e 0,8 dB num dos modelos nas velocidades anteriormente mencionadas, após ajustes para os requisitos de caudal. Por fim, foi descoberto que adicionar cavidades a regiões da superfície de ventiladores com tendência para separações de fluxo de ar pode prevenir este fenómeno e reduzir a energia cinética turbulenta, favorecendo o ruído da camada limite. Este fenómeno torna-se mais evidente em condições de operação perto do stall aerodinâmico. Não se registaram melhorias significativas no modelo com arestas serradas. Medições experimentais realizadas num túnel entálpico e numa câmara semi-anecóica dos três protótipos impressos à escala reduzida mostraram melhorias na ordem dos 3,7 e 5,3 dB(A), a 350 rpm, com os modelos com cavidades e com arestas serradas, contudo novas medições devem ser conduzidas com igual qualidade de impressão para confirmação dos resultados
Mestrado em Engenharia Mecânica

碩士
國立勤益科技大學
冷凍空調系
105
Axial fans are now widely used in cooling systems, especially in the outdoor unit of air-conditioning systems. This fan serves to cool the outdoor unit device which will affect the efficiency of air conditioning systems. Make it more saving the energy and better environmental comfort. In order to achieve excellent heat dissipation, the fan must have excellent design. The purpose of this paper is to study the Computational Fluid Dynamics (CFD) technique, and plotted the new fan cooling design into the cooling fan curve (P-Q Curve), and compare the air volume under different hydrostatic conditions. To achieve the results of the comparison, the value of this experiment can be used as a reference for designing the fan in the future.

博士
國立臺灣科技大學
機械工程系
107
This study intends to apply Helmholtz resonator on the axial-flow, the mix-flow, and the centrifugal fans for improving their narrow-band noises by an integrated effort of numerical simulation, mockup fabrication, and experimental test. At first, the cascade and design theories are utilized to generate the three-dimensional configuration of each fan type for serving as the reference basis. Next, the flow fields and the acoustic features associated with these fans are simulated and evaluated systematically with the aids of the commercial CFD software Fluent. Subsequently, the thorough understanding on the flow and acoustic features of these fans can be attained and utilized to design proper Helmholtz resonators, which are manufactured via CNC technology and installed on the appropriate location for assessing the associated noise-reduction outcomes via both CFD and experimental techniques. For the axial-flow fan, CFD simulation indicates that the noise reductions caused by resonators designed for the 1st and 2nd harmonic frequencies are 11-19 dB and 20-23 dB on their target frequencies, respectively. Also, the experiments present that resonator designed for the first characteristic frequency has the best noise-reduction effects, which are 20.0 and 1.0 dB on the 2nd harmonics and the overall noise, respectively. Regarding the mix-flow fan, numerical calculation predicts that the noise reductions caused by Helmholtz resonators designed for the 1st and the 2nd harmonic frequencies are 2-7 dB and 4-9 dB on their target frequencies, respectively. Also, the experiments illustrate the best noise-reduction effects on the 1st and the 2nd harmonics are 5.4 and 6.9 dB, which are not deviated too much from CFD result. However, the application of resonator on the centrifugal fan is not as effective as the above two fan types. CFD outcomes show that the noise decreases of 3.3 dB and 4.6 dB are achieved on the 1st characteristic frequency by the installation of two resonator designs aimed at the first harmonics. In addition. the smaller noise -reduction effects are found as 1.5 dB and 1.9 dB via the acoustic test inside a semi-anechoic chamber. Generally, the trend and deviation between CFD and test results are correlated and within an acceptable range. In conclusion, the accomplishment of this study provides a systematic design scheme for the application of Helmholtz resonator on three common-used fan types. Several design parameters and installation locations of Helmholtz resonator are analyzed and discussed in a rigorous manner here.