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To improve the performance of the aerodynamic properties and reduce the aerodynamic noise of an axial flow fan in the outdoor unit of an air conditioner, this study proposed a bionic forked trailing-edge structure inspired by the forked fish caudal fin and implemented by modifying the trailing edge of the prototype fan. The effect of the bionic forked trailing edge on the aerodynamic and aeroacoustic performance was investigated experimentally, and detailed analyses of the blade load and internal vortex structures were performed based on large-eddy simulations (LES). It is shown that the bionic forked trailing edge could effectively adjust the blade load distribution, reduce the pressure difference between the pressure side and suction side near the trailing edge of the blade tip region, and weaken the intensity and influence range of the inlet vortex (IV) and the tip leakage vortex (TLV). The discrete noise caused by the vortices in the rotor tip area was also reduced, particularly at the blade passing frequency (BPF) and its harmonic frequency. The experimental results confirmed the existence of an optimal bionic forked trailing-edge structure, resulting in the maximum power-saving rate γ of 7.5% and the reduction of 0.3 ~ 0.8 dB of aerodynamic noise, with an included angle θt of 13.5°. The detailed analysis of the internal vortex structures provides a good reference for the efficiency improvement and noise reduction of axial flow fans.

The present study introduces an innovative aerodynamic redesign of an axial flow fan based on constant diffusion factor and radial equilibrium. All input design parameters such as mass flow rate, hub to tip ratio, aspect ratio, tip diameter and angular velocity are taken from NASA Rotor 67 as a conventional axial flow fan. A computer program is developed to extract the three-dimensional geometry of a fan and to estimate the span-wise distribution of parameters. The new designed fan flow field is investigated in detail by CFD tool at both design and off design conditions. Finally, a turbofan cycle analysis is conducted based on thermodynamic and gas dynamic principles to evaluate the fan performance in a turbofan engine in comparison to NASA Rotor 67. Achieving a higher total pressure ratio, meeting the target pressure ratio in lower rotational speed with higher efficiency, delivering more bypass air in a constant diameter and less fuel consumption for the same specific thrust force are the main advantages for the new design strategy in comparison to the conventional designed fans such as Rotor 67. However, efficiency reduction in fan over speed is the main disadvantage.

This paper presents a critical overview on worst-case design scenarios for which low-speed axial flow fans may exhibit an increased risk of blade resonance due to profile vortex shedding. To set up a design example, a circular-arc-cambered plate of 8% relative curvature is investigated in twofold approaches of blade mechanics and aerodynamics. For these purposes, the frequency of the first bending mode of a plate of arbitrary circular camber is expressed by modeling the fan blade as a cantilever beam. Furthermore, an iterative blade design method is developed for checking the risky scenarios for which spanwise and spatially coherent shed vortices, stimulating pronounced vibration and noise, may occur. Coupling these two approaches, cases for vortex-induced blade resonance are set up. Opposing this basis, design guidelines are elaborated upon for avoiding such resonance. Based on the approach presented herein, guidelines are also developed for moderating the annoyance due to the vortex shedding noise.

Bu çalışmada eksenel fan modeli kullanılarak rotor ve stator kademeleri arasında tanımlanan etkileşim yüzeyi modellerinin ve rotor kanadı profilleri üzerinde uygulanan kaydırma yönteminin etkileri HAD analizleri yapılarak incelenmiştir. Turbomakinelerin HAD analizlerinde rotor ve stator kademeleri arasındaki geçişler için tanımlanan duran çark (frozen rotor), karışım yüzeyi (stage-mixing plane) ve zamana bağlı rotor stator (transient rotor-stator) modeli olmak üzere üç farklı model bulunmaktadır. Tezin ilk bölümünde bu üç modelin referans eksenel fan modelinin performansına etkisini incelemek için zamandan bağımsız analizlerde kullanılan duran çark ve karışım yüzeyi modelleri ile zamana bağlı analizler için geliştirilen zamana bağlı kanat kademesi (transient blade row) modellerinden zaman dönüşümü (time transformation) modelleri kullanılarak analizler gerçekleştirilmiş ve sonuçlar değerlendirilmiştir. Analizler, belirlenen devir sayısında ilk olarak zamandan bağımsız rotor-stator etkileşim yüzeyi modellerinden duran çark ve karışım yüzeyi modelleriyle çözülmüştür. Daha sonra başlangıç şartları karışım yüzeyi çözümleri tanıtılarak zamana bağlı kanat kademesi modellerinden, zaman dönüşümü yöntemiyle çözülmüş ve analiz sonuçları farklı performans parametreleri üzerinden kıyaslanmıştır. Üç farklı etkileşim yüzeyi modeli kullanılarak analiz edilen eksenel fan modeli analizi sonuçları kıyaslandığında, karışım yüzeyi ve duran çark modelleri ile elde edilen statik basınç ve verim eğrilerinin birbirlerine yakın sonuçlar verdiği, zaman dönüşümü modelinin ise bu iki modelden özellikle düşük debilerde daha fazla statik basınç artışı ve verim oluşturduğu görülmüştür. Daha sonra bu üç yöntemle elde edilen HAD analizi sonuçları son işleyici modülü üzerinden, rotor ve stator kanatları üzerinde oluşan basınç ve hız dağılımları, akım çizgileri ve kanat üzerinde oluşan basınç dağılımları gibi parametrelerce farklı kanat kesitlerinde incelenmiştir.Çalışmanın ikinci bölümünde ise eksenel fanlarda kanat profillerinin taşınması uygulamalarından kaydırma yöntemi, refereans fan modeli rotor kanatlarına uygulanmıştır. Rotor kanadı profilleri, kanat kesidinin veter uzunluğu doğrultusunda öne ve arkaya doğru 30°'lik açıda kaydırılarak iki farklı model elde edilmiştir. Kaydırma yöntemiyle hazırlanan fan modelleri ilk olarak karışım yüzeyi modeliyle analiz edilerek performans eğrileri incelenmiştir. Kaydırma uygulanan modeller ile referans fan modelinin debiye göre statik basınç artışları ve verim eğrileri birbirinden farklı sonuçlar ortaya çıkarmıştır. Öne doğru kaydırma uygulanan rotor modeli fanın çalışma aralığını genişletmiş ancak düşük debilere kaydırmıştır. Arkaya doğru kaydırma uygulanan model ise tam tersi fanın çalışma aralığını daraltmış fakat daha yüksek debilerde akış geçirdiği görülmüştür. Verim eğrisi incelendiğinde ise öne doğru kaydırma uygulanan modelin rererans fana göre nispeten daha yüksek değerler verdiği, arkaya doğru kaydırma uygulanan modelin ise daha düşük değerlerde verim sağladığı görülmüştür. Daha sonrasında analizler sonucunda, rotor kanatları üzerinde farklı kesitlerdeki boyutsuz basınç katsayısına göre basınç dağılımları incelendiğinde ise öne doğru kaydırma uygulanan modelin referans modele göre aerodinamik yükü bir miktar azalttığı, arkaya doğru kaydırma uygulanan modelin ise aerodinamik kanat yükünü arttırdığı görülmüştür. Son olarak, kaydırma uygulanan modeller karışım yüzeyi modeli çözümlerine ek olarak en yüksek verim noktalarındaki debiler için duran çark ve zaman dönüşümü modelleriyle da analiz edilerek sonuçlar değerlendirilmiştir. Hesaplamalı akışkanlar dinamiği analizleri, ANSYS CFX 17.2 üzerinden gerçekleştirilmiştir. Fan katı modelinin geometrisi, ANSYS DesignModeler modülü kullanılarak oluşturulmuş ve ağ yapıları hazırlanmak üzere ANSYS TurboGrid modülüne aktarılmıştır. TurboGrid ile rotor ve stator kademeleri kanatları için çözüm ağları hazırlanmıştır. Hazırlanan çözüm ağlarının, ağdan bağımsız sonuçlar verdiği ve y+ değerlerinin kabul edilebilir düzeyde olduğu değerlendirmesi yapılmasının ardından orta sıklıktaki ağ yapısı üzerinden çalışmalara devam edilmiştir. Hazırlanan çözüm ağları ANSYS CFX programına aktarılarak akış koşulları ve çözüm parametreleri tanıtılmıştır. Akış bölgesi, zaman dönüşümü modeli uygulanmasında gerekli olan aralık (pitch) koşulunun sağlanabilmesi için 5 stator ve giriş hacmi ile birlikte 3 rotor ve çıkış hacmi şeklinde periyodik sınır koşulları uygulanarak modellenmiştir. Daha sonra ön işleyici (CFX-Pre) modül üzerinden akış özellikleri, sınır şartları, akış bölgesi ara yüzeyleri ve çözüm kontrol parametreleri tanımlanmıştır. Analizlerde SST k-w türbülans modeli tercih edilmiştir. Hesaplamalar, çözücü (CFX-Solver) modülü üzerinden yapılarak son işleyici (CFD-Post) modülü ile analiz sonuçları görüntülenmiştir. Bu çalışma ile hem dönen ve dönmeyen hacimlerden oluşan eksenel fanlar arasındaki arayüzler için tanımlanan rotor stator etkileşim yüzeyi modellerinin hem de literatürde farklı değerlendirmeler yapılan kanat profillerine kaydırma uygulamasının fan performansına etkileri incelenmiştir. Çalışma sonucunda iki konuda da literatüre katkıda bulunacak sonuçlar elde edilmiş ve değerlendirmelerde bulunulmuştur. In this study, the influence of rotor-stator frame change (mixing plane) models and the influence of sweep on rotor blade profiles of axial flow fan are examined by CFD analysis. There are three different frame change methods defined for the passages between rotor and stator stages in CFD analysis of turbomachines which are frozen rotor, mixing plane (stage) and transient rotor-stator. In the first part of the thesis, the effect of these three methods on the performance of the reference axial fan model is analyzed. Frozen rotor and mixing plane (stage) methods are used in steady analysis and time transformation method from transient blade row model is used in unsteady analysis. First of all, analyzes are solved by using frozen rotor and mixing plane models from the steady rotor-stator frame change models at the specified revolutions per minute. Then, using the mixing plane analyzes results as initial conditions, the reference axial fan model is analyzed with time transformation method from the transient blade row models. Results are obtained over six operating points to get more accurate performance curves. After the end of analyzes, results are compared with different performance parameters. The performance of reference axial flow fan model are compared according to the results three different frame change models. Consequently, the pressure and efficiency curves obtained by mixing plane and frozen rotor models give similar results. However, it has been seen that the time transformation method produces more static pressure rise and higher efficiency compared to these two models, especially at low mass flow rates. Furthermore, the results of CFD analysis by using these three methods are examined in different blade sections for different parameters, such as pressure distributions on the rotor blades and also streamlines, pressure contours and velocity vectors which show flow characteristics on the rotor and stator blades.In the second section of the thesis, the sweep method which shifts blade profiles in the direction perpendicular to the chord is applied on reference axial fan rotor blades. In open literature, there are many studies about the sweep method for turbomachines but as a result of the studies, there are some contradictory explanations when evaluating the effects of the method on the turbomachine performance. In this study, forward and backward sweep with 30° sweep angle is applied to the rotor blades and two different rotor blade models are obtained as a result of this process.First, these forward and backward sweep fan models are analyzed by using mixing plane (stage) model. Thus, the aerodynamic performance curves and flow fields of these fans are calculated. When the swept models are compared to the results of reference fan model analysis, static pressure rise and efficiency curves are observed different from each other. Forward sweep increases the static pressure rise and the efficiency of the fan. However, forward sweep expands the fan's operating range, but shifts to lower mass flow rates. On the contrary, backward sweep decreases the static pressure rise and efficiency of the fan. Nevertheless, operating range of the fan is shifted to the higher mass flow rates, besides, this operating range gets narrowed . In addition to these results, pressure distributions on the rotor blades with the dimensionless pressure coefficient in the different blade sections are examined. Consequently, forward sweep model reduces the aerodynamic load sligthly with respect to the reference model and the backward sweep model increases the aerodynamic blade load compared to other models. Finally, in addition to the mixing plane (stage) analyzes, sweep models are also analyzed by means of the frozen rotor and time transformation methods for the highest efficiency points.Computational Fluid Dynamics (CFD) analyzes are performed using ANSYS CFX 17.2 analysis program. First, existing reference axial fan CAD geometry is imported into ANSYS DesignModeler, then blade geometries of the reference fan model are prepared by using ANSYS DesignModeler module. Then, the CFD meshes of rotor and stator blades are generated using ANSYS TurboGrid. Three different sequences of meshes (rough, medium and frequent) are generated to assess the mesh dependence of the simulations. As a result of this process, mesh dependency and y+ values of boundary layers are checked and the analyses are carried out with the medium frequency mesh structures. The number of mesh elements for stator and rotor are around 0.55 million and 1.15 million respectively. Then, model setup and numerical simulations are carried out with ANSYS CFX. Model setup consists of defined fluid domains, flow conditions, periodic interfaces, frame change models, turbulance model and solution parameters. Fluid domain involves four different parts; inlet, stator, rotor and outlet. Of these domains, inlet, stator and outlet parts are stationary whereas rotor composes the rotational part. For numerical simulations, to avoid convergence problems , inlet and outlet volumes of the flow domains are added to reference axial fan rotor and stator domains. Furthermore, in order to avoid the time problem depending on the number of mesh, rotational periodicity is used for analyzes. However, transient CFD calculations of multistage turbomachines, which are already in the design process, are limited due to computational power and the computational domain which is needed to enforce spatial and temporal periodicity because of unequal blade counts and pitches. Thus, one main issue is to maintain the periodicity by reducing the number of blade passages in each blade row. Therefore, the fluid domains are modeled as 3 rotor blades and output volume with 5 stator blades and input volume to provide the pitch interval needed to implement the time transformation approach. SST k-w turbulence model is used in all simulations. The k-w based Shear Stress Transport (SST) model was designed to give highly accurate predictions of the onset and the amount of the flow separation under adverse pressure gradients by the inclusion of transport effects into the formulation of the eddy viscosity. This results in a major improvement in terms of the flow separation predictions. Morever, a target is set for all normalised RMS residuals to be below 10-5. While it is important to drive the equation residuals to negligible iteration error, it is also important to monitor overall quantities such as mass conservation, pressure ratio and efficiency as a function of iteration. Finally, calculations are generated via the CFX-Solver module and the analysis results are displayed with CFD-Post module.As a result of this study, rotor-stator frame change (mixing plane) methods and the sweep on rotor blade profiles of axial flow fan are examined and consequently axial fan performance and flow characteristics are investigated with several performance parameters. Furthermore, valuable results are obtained at the end of the study for both subjects which would contribute to the open literature. 125

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-e 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.

Radial-vaned air separators produce strong stall improvement effect in axial flow fans. Changes in the fan internal flow patterns achieved by the device are confirmed by Pitot traverse measurements. For the air separator condition, with a decrease in the fan flow rate the meridional streamline inclinations through the rotor blades have become increasingly steep and the circumferential velocities increase toward the tip region, in contrast to relatively little changes in the behaviors of the streamlines and flow patterns in the solid wall condition. It is suggested that the stall suppression is achieved by a combination of the following effects of the air separator; (1) suction of casing boundary layers and elimination of embryos of stall, (2) separation of reversed flow from the main flow, (3) induction of the flow toward the casing wall and strengthening of meridional streamline inclination, thus keeping the Euler head increasing, and (4) reinforcement of axi-symmetric flow structure. Appearance of these effects in the descending order is considered to achieve the great stall suppression effect that would be difficult by other types of stall prevention devices.

The flow field at the rotor exit of a low aspect ratio axial flow fan for different tip geometries and for different flow coefficients is measured in the present study. The following configurations are tested: (1) rotor without partial shroud, designated as rotor (wos), (2) rotor with partial shroud, designated as rotor (ws), and (3) rotor with perforated (perforations in the shape of discrete circular holes) partial shroud, designated as rotor (wps). From steady state measurements, the performance of rotor (wps) is found to be the best. Both the rotors with partial shrouds have stalled at a higher flow coefficient compared to that of rotor (wos). From periodic flow measurements, it is concluded that the low velocity region near the tip section is considerably reduced with the use of partial shrouds with perforations. The extent of this low velocity region for both rotor (wos) and rotor (wps) increases with decreasing flow coefficient due to increased stage loading. This core of low momentum fluid has moved inwards of the annulus and towards the pressure side as the flow coefficient decreases. The extent of the low momentum fluid is smaller for rotor (wps) than that of rotor (wos) at all flow coefficients. Copyright � 2011 N. Sitaram and G. Ch. V. Sivakumar.

Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis. Two kinds of hub-cap, rounded and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. In case of right-angled front shape, axisymmetric distorted inflow is induced by flow separation at the sharp edge of hub-cap, and the characteristics of the inflow depend on the distance between hub-cap and blade leading edge. Three-dimensional Reynolds-averaged Navier-Stokes equations are introduced to analyze the flow characteristics inside the blade passage. Numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results that non-uniform axial inlet velocity profile near the hub results in the change of inlet flow angle. Large recirculation flow upstream the fan rotor for the right-angled hub-cap induces separated flow on the blade surfaces near the hub region, and thus deteriorates the performance of fan rotor. The effect of the distance between hub-cap and blade leading edge on the efficiency is also discussed.

In this work, the time varying stresses in a Howden axial flow fan are obtained by finite element analyses. Dynamic substructuring is used to obtain accurate values of the stresses in the threads of the blade shaft, the component which connects the blade with the hub. Three different global models are used to compare the influence of neglecting the fan shaft and the stiffness influence of the centrifugal force. The relative displacements, which are obtained from the global models, have been used as boundary condition in the detailed models. The detailed models are used to obtain the Von Mises stresses in the root of the threads of the blade shaft. Finally the results of the three global models are compared with experimental measured data provided by Howden. The experimental data results in the highest Von Mises stresses. The model with the fan shaft and the stiffness influence of the centrifugal force gives values for the Von Mises stresses which are approximately twenty percent lower. The model without the fan shaft results in the lowest stresses which are approximately forty percent lower than the stresses obtained using the measured data.

Turbo makine akışlarının eksenel-simetrik modelleri, tersine tasarım, analiz ve test verisinin işlenmesinde ana araçlardır. Bu metodların gücü, bu akışların esasen çevreselde ortalanmış akışta rotor ve stator kaynaklı akış döngüleri ile temsil edilebilmesinden kaynaklanmaktadır. Bu sayede hesaplama süresi üç boyutlu analiz metodlarının en az yüzde biri mertebesindedir. Bunu gerçekleştirmenin yolu ise turbo makine enerji denklemleri ile birlikte görgül kanatçık basınç kaybı, isabet açısı, sapma açısı ve tıkama modellerinin her kanadın kökünden ucuna kadar akış çözümüne tanımlanmasıdır. Konu kompresör ve türbinler için açık literatürde birçok açıdan çalışılmasına rağmen turbofan motorların fan ve ayırıcı sistemlerinin tersine tasarımı için yapılan çalışmalar çok kısıtlıdır.Bu çalışmanın amacı, bu eksikliği gidermek için yeni bir ayrık akış metodunun akım çizgisi eğriliği tersten akış çözüm metodu için geliştirilmesidir. Çözücüye eklenecek görgül modeller ise literatürden kalibre edilmek üzere derlenmiştir.Metod hem deneysel hem de sayısal veri ile toplam altı değişik model üzerinde üç aşamada doğrulanmıştır. İlk olarak, kanatçık içermeyen ve sadece eksenel-simetrik ayrık akışlı kanal çözümünü doğrulamak için tasarlanan üç farklı model kullanılmıştır. Sonraki aşamada bahsi geçen görgül modeller transonik ve ayrık akış içermeyen NASA 2-kademe fanı ve tezin kapsamında tasarlanmış fan kademesi üzerinde sırasıyla deneysel ve sayısal verilerle doğrulanmıştır. Son aşamada ise GE-NASA ayrık akışlı fan sistemi kullanılarak tüm modellerin deneysel doğrulaması yapılmıştır.İncelenen geometriler için hesaplamalarda gözlemlenen en büyük hatalar basınç oranı için 1.6%, verim için 2.3%, hız için 8% ve akış açısı için 1.8 derecedir. Tüm bu çalışmalar sonucunda geliştirilen metodun doğruluğu gösterilmiştir ve mevcutta bulunan ayrık akış içermeyen kompresör eksenel-simetrik metodlarına asgari çaba ile uygulanabilirdir. Through-flow modeling of turbomachinery flows is the principle tool for inverse design, off-design analysis and post-processing of test data, due to its capability to simulate the principal aspects of turbomachinery flows, swirling flow with rotors and stators, in the axisymmetric meridian plane with minimum two orders of magnitude smaller computational time compared to three-dimensional analysis methods. Turbomachine energy equation and empirical models for incidence, deviation, pressure loss and blockage are used to define source terms for an axisymmetric compressible flow solution. Even though the subject has been studied in numerous aspects for compressors and turbines, open literature on fully coupled fan and splitter design of turbofan engines is still limited. The present study addresses this void by developing a new split-flow method for inverse streamline curvature flow solution methodology in the course of this thesis. Hybridized empirical models that are compiled from the literature are implemented as a baseline to be calibrated.The method is validated both experimentally and numerically on a total of six different test cases within a three-step validation strategy. Firstly, split-flow solutions of the developed method for three representative duct geometries, but without a turbomachinery, are validated. Secondly, two different single-stream transonic fans, NASA 2-stage fan and a custom-designed fan stage are used to experimentally and numerically validate the empirical models, respectively. Thirdly, experimental data of GE-NASA by-pass fan is used to validate the complete models.It is shown that the accuracy of solutions in the tested cases are within less than 1.6% in pressure ratio, 2.3% in efficiency, 8% in velocity and 1.8 degree in flow angle. With this accuracy level, the proposed method is shown to be valid and can be implemented into existing compressor streamline curvature methodologies with minimal numerical effort. 181

Three dimensional steady and unsteady velocity distributions in the axial flow fan were measured using a hot wire probe for various operational conditions, various rotational speeds and various measuring positions. For measuring the velocity distributions in the blade passage, a specially designed and manufactured hot wire traversing apparatus was used. Steady velocity distributions, turning angles, effects of incident to the cascade, flow leakage through the tip clearance and effects of the flow separation show the flow phenomena through the blade passages. Unsteady velocity distributions show time dependent procedures of the wake flowing through the moving blade passage. Considering these results of measurements, the effects of the upstream stationary blade and the effects of Reynolds number on the flow were considered.

oz EKSENEL AKIŞLI BİR FANIN GİRİŞİNDEKİ AKIŞ DÜZENSİZLİKLERİ GÜRÜN, Akif Murat Yüksek Lisans, Makina Mühendisliği Bölümü Tez Yöneticisi: Prof. Dr. O. Cahit Eralp Yardımcı Tez Yöneticisi: Prof. Dr. Kahraman Albayrak Nisan 2002, 235 sayfa Bu çalışmada, eksenel akışlı bir fanın giriş ve çıkışında üç boyutlu hız ölçümleri, bir veri alma sistemine bağlanan sıcak tel anemometresi kullanılarak incelenmiştir, ölçümlerde tek boyutlu eğik kızgın tel tekniği kullanılmıştır. Deneyler, Deney Dizayn tekniği kullanarak hazırlanmıştır. Üç boyutlu türbulans şiddetleri ve düzensiz giriş akışlı fan verimlilik eğrileri, üç plakanın ön, alt, sağ olmak üzere ahi değişik giriş konfigurasyonunda ve üç ayrı akış miktarında incelenmiştir. Akış düzensizliklerinin türbulans şiddetine etkileri ve bunun sonucunda fanın performansına olan etkileri incelenmiştir. Bütün veriler MINITAB yazılımı ANOVA araçları kullanılarak istatiksel olarak incelenmiştir. Akış miktarının fan girişinde alt plakanın varlığında azaldığı, fan yükünün artmasıyla arttığı görülmüştür. Ayrıca, bunların ikisinin birden de etkili olduğu gözlenmiştir. Parelel olarak, alt plakanın, fan yükünün ve de ikisinin birden toplam verimliliği etkilediği bulunmuştur. Öte yandan statik verimliliğin sadece fan yüküne bağlı olduğu görülmüştür. Ayrıca, giriş konfigurasyonunun ve akış rniktarının türbulans yoğunluklarına ve ortalama hıza olan etkileri de incelenmiştir. X eksenindeki türbulans yoğunluğunun kontrol altında tutulan hiçbir değişkenle ilgisi saptanamamıştır, öte yandan, y eksenindeki yoğunluğun ah plakaya, z eksenindeki yoğunluğun ise akış miktarıyla ilgili olduğu saptanmıştır. Bu eksenlerdeki türbulans yoğunluğunun geometrik ortalaması olarak tanımlanan birleştirilmiş ortalama türbulans yoğunluğunun ise fan yüküne bağlı olduğu gözlenmiştir. İokümaniasyon mekkbsBSonuç olarak turbülans yoğunluğunun fen performansı için bir etken olmadığı bulunmuştur, Akış miktarı bir soğutma fanı için en önemli değişken olup ağırlıklı olarak fan yüküne bağlı olduğu girişteki düzensizliklerden etkilenmediği görülmüştür. Anahtar Kelimeler: Eksenel Akışlı Fan, Eğik Sıcak Tel Anemometresi, Veri Alımı, Deney Dizaynı, Fan Verimlilik Eğrileri, ANOVA VI ıremenntöt «.rtP-KEr* ABSTRACT INLET FLOW DISTORTIONS ON AN AXIAL FLOW FAN GÜRÜN, Akif Murat M.S., Department of Mechanical Engineering Supervisor: Prof Dr. O. Cahit ERALP Co-Supervisor: Prof Dr. Kahraman ALBAYRAK April 2002, 235 pages In this study, the three-dimensional velocity field of an axial flow research fen at the inlet is examined using a constant-temperature hot wire anemometer connected to a data acquisition system. The single slanted sensor hot wire technique is used in the measurements. The experiments are designed using Design of Experiments (DOE) technique. The three-dimensional turbulence intensities and distorted fen performance curves are determined for six different inlet configurations of three plates distorting the inlet, namely front, bottom, right and three flow rates. The effect of inlet flow distortions on the turbulence intensities, hence on the performance of the fen is investigated. All the measurements are analyzed statistically with MINITAB software using ANOVA tools. It has been found that the flow rate decreases when there is plate at the bottom of the fen inlet and increases with the throttling. Additionally, the bottom plate and throttling have a combined effect on the flow rate. In parallel, the bottom plate and throttling affect the total efficiency, having also a combined effect, on the other hand the static efficiency depends only on throttling. Moreover, the effects of inlet configuration and throttling on the turbulence intensities and mean velocity are also investigated. The turbulence intensity in the x-axis is found to dependent on none of the controlled parameters, but y-intensity depends on bottom plate and z-intensity on throttling. A combined mean turbulence intensity is defined as the geometric mean of these intensities and it is found to be dependent on the throttling. It has been observed that the turbulence intensity is not an effective parameter on the performance of the fen. The most important parameter for a cooling fen is inthe flow rate and it mostly depends on throttling as expected and is mainly insensitive to the distortions at the inlet. Key Words: Axial Flow Fan, Slanted Hot Wire Anemometer Technique, Data Acquisition, Design of Experiments, Fan Performance Curves, ANOVA IV 235

öz EKSENEL AKIŞLI BİR FANIN GİRİŞİNDEKİ AKIŞ DÜZENSİZLİKLERİ BÖGE, Ali Cem Yüksek Lisans, Makina Mühendisliği Bölümü Tez Yöneticisi : Prof. Dr. O. Cahit Eralp Eylül 2000, 203 Sayfa Bu çalışmada, eksenel akışlı bir fanın giriş ve çıkışında üç boyutlu hız ölçümleri, sıcak tel anemometresi kullanılarak incelenmiştir. Ölçümlerde tek boyutlu eğik kızgın tel tekniği kullanılmıştır. Fanın giriş ve çıkışında, statik ve toplam basmç ölçümleri yapılmıştır. Fan performans grafikleri, AMCA 210-85 Standardına göre hesaplanmıştır. Anahtar Kelimeler : Eksenel Akışlı Fan, Eğik Sıcak Tel Anemometresi, Basmç Dağılımı, Fan Performans Eğrileri IV ABSTRACT INLET FLOW DISTORTIONS ON AN AXIAL FLOW FAN BÖGE, Ali Cem M.S., Department of Mechanical Engineering Supervisor : Prof. Dr. O. Cahit Eralp September 2000, 203 pages In this study, the three mean velocity components, namely tangential, radial and axial velocities at the inlet and at the exit of an axial flow research fan is examined by using hot wire anemometer. The single slanted sensor hot wire technique is used in the measurements. The static and the total pressure distributions at the inlet and the exit of the fan are examined. The fan performance curves are obtained according to the AMCA 210-85 Standard. Key Words : Axial Flow Fan, Slanted Hot Wire Anemometer Technique, Pressure Distribution, Fan Performance Curves 111 203