O trabalho aqui apresentado visa estudar diferentes tipos de piso localizados na seção de testes de um túnel de vento e verificar a influência que ocorre em ensaios de automóveis analisando o escoamento entre o veículo e o solo, assim como avaliar alterações no coeficiente de arrasto, utilizando simulações numéricas computacionais. O coeficiente de arrasto de um veículo é uma propriedade aerodinâmica importante e, quanto menor for esse valor, melhor será seu rendimento, além de melhorar o consumo de combustível, item relevante hoje no projeto de novos automóveis. Partindo de um ensaio experimental de uma pequena caminhonete em túnel de vento com piso fixo, um modelo virtual igual é construído e analisado por CFD, nas mesmas condições de teste do ensaio real. A diferença de resultado entre o coeficiente de arrasto medido em túnel de vento e o cálculo por simulação é de 0,25%, mostrando que o método de simulação possui grande confiabilidade. Posteriormente, outras duas simulações considerando dois outros tipos de solo: plataforma elevada e esteira rolante são analisadas e apresentaram diferenças de decréscimo valor de arrasto de 0,002 e 0,012 respectivamente, em relação a simulação com piso fixo, mostrando a influência de alterar o tipo do solo na seção de testes do túnel de vento. O comportamento do escoamento de ar é visualizado através de imagens do campo de velocidades e de pressões, sendo caracterizadas a camada limite e regiões de estagnação. Complementarmente, são realizados dois estudos: o primeiro considerou apenas uma roda isolada em condição de piso fixo e com esteira rolante, na mesma seção de testes do túnel de vento, visando medir a influência de mudar tipos de solo, sem utilizar um veículo completo, economizando em processamento e preparação de modelo. O segundo estudo considerou 3 diferentes tamanhos de malha sendo eles 5, 10 e 20 mm e medir a influência disso no resultado do coeficiente de arrasto obtido. / The work here presented aims to study different types of ground configurations, located at the test section of a wind tunnel and check their influence on the drag coefficient of one car, using only computer simulations. The drag coefficient of a vehicle is one of the most important aerodynamic proprieties, and as low as this drag value can be, the car performance will increase and the fuel consumption will decrease, item which has been persued in new vehicles. Starting from one real wind tunnel test of a small pick-up, with static test section ground, a virtual model was built and tested using CFD, following the same configuration of the real test. The difference between test and simulation results was 0.25%, showing that the methodology here used is reliable. After that, two other types of ground were simulated: elevated plate and moving belt and the results show that drag value decreased 0.002 and 0.012 respectively, compared to the value obtained with static ground simulation. The flow behavior is demonstrated with colored images of the velocity and the pressure fields. As a complement for this work, two other cases were studied: the first one analyzed one isolated wheel in two different types of ground: static and moving belt, at the same wind tunnel test section, aiming to measure the influence of these types of ground, without the need of using a complete car, saving computational and modeling time. The second study shows the influence of mesh size, considering three cases: 5, 10 and 20 mm, in order to evaluate the influences of it on drag coefficient results provided by CFD.

Desde o início da década de 2010, o aumento do preço do combustível de aviação e a pressão da sociedade para redução da emissão de gases nocivos ao meio ambiente, junto com a necessidade de redução de ruído durante as fases de decolagem e pouso, levaram as companhias aéreas a buscar aeronaves mais eficientes. Para suprir essa demanda, os fabricantes de aviões comerciais solucionaram esse problema através do uso de motores de maior desempenho, que apresentam maior diâmetro que motores de gerações passadas. Desse modo, foi necessário projetar asas com maior diedro na região da raiz, possibilitando a instalação desses novos motores, e diedro menor após a seção do motor, adotando assim a solução de asa em gaivota. O presente trabalho visa analisar o impacto de diferentes tipos de asas em gaivota nos coeficientes aerodinâmicos de uma aeronave de configuração comercial típica. Para tanto, foi realizada uma revisão bibliográfica dos estudos envolvendo asas em gaivota. Numa primeira fase foi feito um estudo analítico das características aerodinâmicas de alguns modelos de aeronaves com asa em gaivota, e em uma segunda fase, foram empregadas ferramentas computacionais para analisar seus comportamentos aerodinâmicos. Posteriormente, em uma terceira fase, esses modelos foram ensaiados no túnel de vento do LAE (Laboratório de Aerodinâmica da EESC/USP), e os resultados das três fases foram comparados. / Since the beginning of the 2010s, the increasing price of aviation fuel and the pressure of society to reduce the emission of harmful gases into the environment, coupled with the need of noise reduction during the takeoff and landing, induce carrier companies to look for more efficient airplanes. To furnish this demand, the airplane manufacturers solved the problem using high performance engines, which present a larger diameter than the engines from previous generations. Thereby, it was necessary to project wing with higher dihedral on the root portion, enabling the installation of these new engines, and a lower dihedral after the engine section, thus adopting a gull wing solution. This research project aims at analyzing the impact of different types of gull wing on the aerodynamic coefficients of a typical commercial configuration airplane. For this purpose, a bibliographic review about the studies related to gull wings was performed. In a first phase, an analytical analysis of the aerodynamic characteristics of some airplane model with gull wings was done, and in a second phase, computational programs was used to study their aerodynamic behavior. Later, in a third phase, these models were tested in the wind tunnel of LAE (Laboratory of Aerodynamics of EESC/USP), and the results from the three phases were compared.

A ventilação natural é uma das estratégias mais eficientes para o condicionamento térmico passivo de edificações, ocorrendo por ação dos ventos, por efeito chaminé ou pela combinação de ambos. Em áreas densamente ocupadas, a velocidade do vento é reduzida pelos diversos obstáculos locais, tornando o efeito chaminé e a captação pela cobertura as alternativas mais viáveis para indução da ventilação natural em edificações. Dentre as estratégias de ventilação, destacam-se os sheds, aberturas no telhado, que funcionam como captadores ou extratores de ar, dependendo de sua localização em relação aos ventos dominantes. Apesar de terem um grande potencial, são pouco utilizados devido à falta de dados técnicos acessíveis ao projetista. Além disso, muitas vezes são utilizados para captação ou para extração do ar de forma aleatória, sem uma análise da influência dos parâmetros projetuais na ventilação natural. Essa pesquisa parte da hipótese que existe diferença nesses parâmetros para um shed extrator e para um shed captador de ar e que é possível otimizar a ventilação natural através desses dispositivos. O objetivo geral foi avaliar o impacto de diferentes parâmetros projetuais e climáticos no desempenho de sheds captadores e extratores de ar e propor diretrizes para o projeto desses dispositivos. A metodologia foi composta de estudos paramétricos, a fim de investigar a interdependência de diferentes parâmetros projetuais na ventilação natural por sheds e realizar análises comparativas. O processo baseou-se em análises numéricas através de simulações CFD e a verificação desses resultados por meio de ensaios experimentais em túnel de vento. As análises mostraram uma boa compatibilidade entre os resultados numéricos e experimentais, obtendo uma diferença de no máximo 10% entre as duas ferramentas para a maioria dos pontos monitorados. Com relação às simulações computacionais, constatou-se que o desempenho de sheds é fortemente influenciado pela velocidade e pelos ângulos de incidência dos ventos externos. Além disso, notou-se que existem diferenças nos parâmetros projetuais para um shed extrator e para um captador, sendo que alguns casos apresentaram bons desempenhos em ambas as situações. Por fim, conclui-se que é possível otimizar o uso da ventilação natural através desses dispositivos, sendo que esses resultados auxiliam a prática do projeto arquitetônico na determinação de configurações adequadas. / Natural ventilation is one of the most important strategies for passive cooling of indoor environments. It can occur by wind forces, stack effect or a combination of both strategies. In urban areas the wind speed is reduced due to several obstacles. Stack effect and air intake by the roof can be viable alternatives to induce natural ventilation in buildings. Among the ventilation strategies, sheds can be highlighted. These structures consist of roof openings that work as collectors or extractors of air, depending on their location in relation to the prevailing wind directions. Although they have great potential, they are seldom used by Brazilian architecture, due to lack of technical data available to the designer. Besides, sometimes the sheds are used for air intake or exhaustion without any detailed analysis on the influence of different building design parameters on natural ventilation. The starting hypothesis of this research is that there is a difference in construction parameters for an exhaustion and intake sheds and it is possible to optimize the use of natural ventilation through these devices. The research aims to investigate the potential of air extracting and capturing sheds to promote indoor natural ventilation and proposes guidelines for the design of these devices. The applied methodology consists on parametric studies to investigate the interdependence of different design parameters for natural ventilation in sheds and perform comparative analyzes. The procedure was based on CFD simulations and the verification of such results through experimental tests using wind tunnel. The analyses showed a good compatibility between the numerical and experimental results, obtaining a maximum difference of 10% between the two tools for most of the monitored points. The computer simulations showed that sheds performance is strongly influenced by the external wind speed and its incidence angles. In addition, it was noted that there are differences in design parameters for air extracting and capturing sheds and some cases showed a good performance in both situations. Finally, it was concluded that it is possible to optimize the use of natural ventilation through these devices, and these results support the practice of architectural design in determining appropriate settings.

O presente trabalho busca através do uso de túnel de vento e de análises computacionais via CFD (Computacional Fluid Dynamics) avaliar o comportamento aerodinâmico que determinadas modificações nas arestas vivas de uma edificação retangular propiciam. No que tange a avaliação em túnel de vento, confeccionou-se modelos rígidos com diversas tomadas de pressão distribuídas nas fachadas dos modelos com o propósito de determinar a distribuição das isolinhas médias de pressão e os coeficientes aerodinâmicos. As simulações computacionais foram feitas a partir do uso do método de Taylor-Galerkin de 2 passos em sua forma explícita. Os modelos numéricos foram discretizados segundo o Método dos Elementos Finitos (MEF) utilizando a técnica de integração reduzida e controle de modos espúrios. A turbulência foi tratada utilizando o modelo de turbulência LES (Large Eddy Simulation), um simulador sintético de turbulência e a viscosidade turbulenta segundo a forma dinâmica. Ao final, concluiu-se que as modificações nas arestas vivas de um edifício alto, inicialmente retangular, são capazes de propiciar reduções significativas nas cargas de arrasto e laterais às quais a edificação estaria sujeita sem as modificações propostas. As isolinhas de pressão determinadas mostraram que há uma grande diferença na distribuição de pressões, sendo as modificações nas arestas capazes de diminuir os coeficientes de pressão experimentados pela estrutura. E que o uso integrado de ferramentas experimentais e numéricas pode propiciar um maior conhecimento e confiabilidade nos resultados obtidos na investigação da resposta aerodinâmica de uma estrutura. Além disso, através da comparação entre resultados experimentais e numéricos, viu-se que ambos apresentaram resultados próximos, demonstrando assim, a evolução dos métodos numéricos em avaliações de problemas de interesse da Engenharia do Vento. / The present work aims to evaluate the aerodynamics behavior that certain types of corner modifications in a rectangular building produce by using wind tunnel and computational analysis by CFD. Regarding the wind tunnel tests, rigid models were built using several pressure taps on their facades in order to determine the average pressure isolines distribution and the aerodynamic coefficients of the reduced models. Computational simulations were made using the two-step Taylor-Galerkin method in its explicit form. The numerical models were discretized according to the Finite Element Method (FEM) using the reduced integration technique and hourglassing control. The turbulence was treated using the Large Eddy Simulation (LES) methodology, a synthetic turbulence simulator and the turbulent viscosity according to the dynamic approach. At the end, it was concluded that the corner modifications in a tall building, initially rectangular, are able to produce significant reductions in drag and lift loads to which the building would be subject without the proposed modifications. The determined pressure isolines showed there is a great difference in the pressure distribution, being the corner modifications able to reduce the pressure coefficients experienced by the structure. And that the integrated use of numerical and experimental tools can provide greater knowledge and reliability in the results obtained in the investigation of the aerodynamic response of a structure. In addition, through the comparison between experimental and numerical results, it was observed that both presented close results, thus demonstrating the evolution of numerical methods in evaluations of problems of Wind Engineering interest.

Les phénomènes d’interaction fluide-structure jouent un rôle important dans le calcul de tenue au séisme des assemblages combustibles. Afin de quantifier les marges de dimensionnement, le modèle de forces fluides utilisé doit être validé et affiné. Pour cela, des campagnes d’essais à l’échelle industrielle ont été réalisées en amont de la thèse. L’objectif ici est de contribuer à l’interprétation des essais industriels pour le cas stationnaire, et de valider les méthodes numériques permettant de simuler ce type d’écoulement. La problématique industrielle s'inscrit dans la tradition de l'étude des structures élancées sous écoulement axial. Le modèle de force fluide locale généralement utilisé, que nous appelons modèle de Taylor-Lighthill-Païdoussis (TLP), consiste en stationnaire à combiner un terme de force fluide potentielle, proportionnel à la courbure, et un terme de force fluide visqueuse, proportionnel à la pente. Des versions dynamiques de ce modèle ont été employées avec succès pour prédire le comportement vibratoire de cylindres flexibles en écoulement axial. Néanmoins, la littérature propose très peu de données de validation directe de cette représentation des forces fluides. Afin d’acquérir de telles données, pour le cas particulier d’un cylindre confiné dans un réseau de cylindres, un nouveau banc d’essai a été conçu et mis en place au laboratoire. Il s’agit d’un faisceau de 3x3 cylindres disposé dans une veine de soufflerie. Le cylindre central possède trois degrés de liberté : rotation, translation, flexion. Les efforts fluides résultants sont mesurés à l’aide d’une balance. Un modèle numérique similaire à la maquette est aussi réalisé et donne accès aux forces fluides locales. Les forces globales obtenues numériquement et expérimentalement sont comparables. Les forces locales obtenues dans les simulations numériques s’expliquent bien à l’aide du modèle TLP, en ignorant les effets de bord à l’entrée et à la sortie du faisceau. La transposition au cas industriel, de géométrie plus complexe, est réalisable par recalage des coefficients du modèle. / Fluid-structure interaction phenomena play a major role in the seismic design of fuel assemblies. In order to evaluate the design margins, the implemented model of fluid forces needs to be carefully assessed. Industrial-scale tests have been carried out with that purpose. Our goal is to contribute to their interpretation in the steady case, and to validate CFD methods usually applied to the type of flow at stake here. This fits in the tradition of the study of slender structures in axial flow. The local steady fluid forces decompose in a potential term, which is proportional to the curvature of the structure, and a viscous term, proportional to the angle of incidence. Adapted versions of this representation, which we call Taylor-Lighthill-Païdoussis (TLP) model, have proved successful in predicting the dynamic behaviour of flexible cylinders in axial flow. However, there is a lack in the literature of sound validation data for the fluid forces themselves. In order to gather such data, a new test rig has been designed and built. It consists in a 3x3 cylinder bundle confined in a wind tunnel. The central cylinder can be rotated, translated or bent. Resultant fluid forces are measured using a load cell. CFD calculations give access to the local fluid forces. CFD and experiments give similar results on the global fluid forces. The TLP model performs well at predicting the local fluid forces, except in the inlet and outlet regions. It can be fitted to the industrial case by adapting its coefficients.

O principal objetivo desta tese é estudar os efeitos inerciais e de pressão do escoamento médio sobre o próprio escoamento médio de jatos bi-dimensionais confinados. Os escoamentos considerados no presente trabalho são turbulentos, isotérmicos, incompressíveis e compostos por fluidos simples. A introdução e a revisão bibliográfica são feitas por meio da apresentação: das motivações tecnológicas e fundamentais para a escolha do tema da presente tese; do cenário no qual a abordagem adotada está inserida; dos parâmetros adimensionais usualmente adotados na literatura para caracterizar os jatos bidimensionais confinados (parâmetros clássicos); e dos dados experimentais levantados na literatura na forma de correlações semi-empíricas, e de perfis de propriedades do escoamento. A presente tese desenvolve uma abordagem integral e adimensional para jatos confinados. As hipóteses adotadas nesta abordagem são aquelas relativas a escoamentos em camada fina cisalhante, e a escoamentos não dissipativos. A abordagem é baseada em balanços integrais de massa e quantidade de movimento. Os termos de quantidade de movimento são classificados como inerciais ou de pressão; e como fluxos, forças ou fontes. Esta classificação permite analisar os efeitos considerados pelos parâmetros adimensionais clássicos. Os parâmetros clássicos não satizfazem simultaneamente às seguintes condições: ser baseado em uma superfície de controle fechada; e ter os efeitos inerciais e de pressão separados em parâmetros distintos. Desta forma, são desenvolvidos dois parâmetros adimensionais novos. Estes parâmetros novos são usados na definição de variáveis adimensionais cuja finalidade é obter uma regra de escalonamento apropriada. A regra de escalonamento desenvolvida é validada por meio de sua aplicação a três bancos de dados de literatura. Esta aplicação mostra a influência dos efeitos inerciais e de pressão sobre o escoamento. A qualidade dos dados experimentais de literatura e próprios também é avaliada pela aplicação desta mesma regra de escalonamento. O túnel de vento construído para estudo de jatos confinados axi-simétricos é apresentado por meio: dos requisitos de projeto; dos critérios de projeto; e da descrição dos componentes. Este túnel possui seção de teste com 300mm de diâmetro e 1500mm de comprimento; contração com razão de área de 4 : 1 e lanças de ar com diâmetros de 10mm, 40mm, 75mm e 150mm. Os procedimentos experimentais adotados na caracterização do escoamento do túnel de vento axi-simétrico incluem: a técnica de determinação do tensor das tensões de Reynolds e do vetor velocidade média em função de medições de velocidade média e de tensão normal de Reynolds em 6 direções distintas; a validação desta técnica; e as correções de posicionamento e de direcionamento do intrumento de medição. O instrumento de medição utilizado foi um anemômetro a laser (LDV). As principais contribuições da presente tese são as seguintes: redesenvolvimento dos parâmetros adimensionais clássicos de jatos confinados por meio de uma metodologia e nomenclatura unificada; proposição de dois parâmetros adimensionais para jatos confinados, um para efeitos inerciais e outro para efeitos de pressão; incremento do banco de dados experimentais referentes a jatos confinados; construção de um túnel de vento axi-simétrico para estudo de jatos confinados; e descoberta da existência de similaridade em jatos confinados com gradiente de pressão elevado. / The main objective of this thesis is to study the mean flow inertial and pressure effects on the mean flow itself in two-dimensional confined jets. The flows considered in the present work are turbulent, isothermal, incompressible and single-fluid. The introduction and the bibliographical review are done by the following presentations: technological and fundamental motivations for the choice of the thesis subject; the scene where the adopted approach is included; dimensionless parameters usually adopted in the literature for two-dimensional confined jets characterization (classic parameters); and experimental data found in literature as semi-empirical correlation, and as mean flow properties profiles. This thesis develops an integral and dimensionless approach for confined jets. The hypotheses adopted in such approach are the thin shear layer approximation, and the non-dissipative flow assumption. The approach is based on mass and momentum integral balances. The terms are classified as inertial or as pressure; and as flux, as force, or as source. Such classification allows the analysis of the effects considered by the dimensionless classic parameters. The classic parameters do not satisfy the following conditions simultaneously: to be based on a closed control surface; and to separate the inertial and pressure effects in distinct parameters. Due to this, two new dimensionless parameters are developed. The new dimensionless parameters are used in dimensionless variables definition whose purpose is to obtain a proper scaling rule. The developed scaling rule is validated applying it to three data banks from literature. This application shows the inertial and pressure effects on the flow. The quality of the literature and the own data bank is evaluated by this scaling rule application. The wind tunnel built for axi-symmetric confined jets studies is presented by: project requirements; project criteria; and components description. This tunnel has a test section with 300mm in diameter and 1500mm in length; contraction area rate of 4 : 1; and air guns with 10mm, 40mm, 75mm and 150mm in diameters. The procedures adopted in the axi-symmetric wind tunnel flow characterization include: the scheme to determine the Reynolds stress tensor and the mean velocity vector from mean velocity and normal Reynolds stress measurements in six distinct directions; this scheme validation; and the positioning and directioning probe corrections. The instrument used was a laser Doppler velocimeter. The main contributions of the present thesis are the following: redevelopment of the confined jets classic dimensionless parameters through an unified methodology and nomenclature; the proposition of two new confined jets dimensionless parameters, one for inertial effects and other for pressure effects. improvement of experimental data bank regarding confined jets; construction of an axi-symmetric wind tunnel for confined jet studies; and the discovery of the similarity existence in confined jets with high pressure gradient.

Aerogeradores, ou turbinas eólicas, são máquinas instaladas em grandes parques eólicos que convertem a energia cinética do vento em energia elétrica. A definição da separação e da interação entre máquinas é um fator fundamental de análise durante a fase de projeto, pois os chamados efeitos de esteira podem inviabilizar o desenvolvimento de um parque eólico. Em geral, a esteira de um aerogerador está caracterizada por um significativo déficit de velocidade e uma intensificação dos níveis de turbulência, o que ocasiona a diminuição da eficiência aerodinâmica e a redução da vida útil das máquinas localizadas a sotavento. Embora existam diferentes pesquisas destinadas à compreensão e previsão dos efeitos de esteira, o problema permanece como uma questão desafiadora que exige a adoção de ferramentas de alta precisão para sua identificação. Este trabalho apresenta uma metodologia experimental em túnel de vento, para a caracterização e avaliação do campo de escoamento na esteira aerodinâmica de um modelo reduzido, sob diferentes condições de escoamento incidente. Especificamente, investiga-se a influência da turbulência atmosférica para quatro perfis de escoamento: i) uniforme-suave; ii) uniforme-turbulento; iii) lei potencial com expoente α = 0,11; iv) lei potencial com expoente α = 0,23. Todos os casos foram conduzidos sob condições de estratificação neutra, e foi utilizado anemômetro de fio-quente para efetivar as medições dos perfis de velocidade média e intensidade da turbulência, em diferentes posições da esteira. Os resultados mostraram diferenças substanciais no comportamento dos perfis de esteira, em função dos níveis de turbulência incidente. Particularmente, observou-se que o incremento da turbulência atmosférica reduz o déficit de velocidade e promove uma maior mistura turbulenta, o que acelera a dissipação dos efeitos de esteira. Assim, a metodologia experimental em túnel de vento evidencia-se como uma importante ferramenta de análise que possibilita amplo espectro para a investigação, precisão e confiabilidade de projetos eólicos. / Wind turbines are machines installed in large wind farms to convert the wind's kinetic energy into electrical power. For an optimal wind farm siting, it is necessary to take into account the interaction between wind turbine wakes. In general, wake effects are associated with velocity deficit and enhanced turbulence intensity. This may reduce the aerodynamic efficiency and lifetime of downwind turbines, making the project unfeasible. Several experimental and numerical studies have been conducted to unravel the behavior of wind turbine wakes under different inflow conditions. However, current wind farm siting tools are incapable of accurately predicting and assessing its effects. This document presents an experimental methodology in the wind tunnel to survey the influence of the atmospheric turbulence on the wake flow field of a wind turbine model. Specifically, four different flow conditions were investigated: i) uniform-laminar; ii) uniform-turbulent; iii) power law exponent α = 0.11; iv) power law exponent α = 0.23. All cases were developed under neutrally stratified conditions. Hot-wire anemometry was used to obtain high-resolution measurements of the mean velocity and turbulence intensity profiles at different downwind positions. Results show that different turbulence intensity levels of the incoming flow lead to substantial differences in the spatial distribution of the wakes. Particularly, higher ambient turbulence promotes a faster wake recovery and lower velocity deficit. In conclusion, the use of wind tunnel experiments is a trustworthy alternative that brings precision and reliability to wind projects.

<div>To reduce the risk of using suction in a hypersonic quiet-tunnel nozzle design, this project tested micro-perforated suction sections to remove the boundary layer on an axisymmetric model in the Boeing/AFOSR Mach-6 Quiet Tunnel. The model was a cone-flare geometry tested at 0° angle of attack. The turn from the 7° half-angle cone to the flare was designed to prevent flow separation. The flare was designed to amplify the Görtler instability.</div><div><br></div><div>Five suction sections were designed with different perforation patterns and porosities. Four were successfully manufactured, but only the first of the four sections has been tested so far. The first suction section has pores drilled along straight lines with a nominal 5% porosity.</div><div><br></div><div>Measurements were made with temperature-sensitive paint and oil-flow visualization on a non-perforated blank to measure the baseline development of Görtler vortices on the flare. Although the signal-to-noise ratio of the measurement techniques were insufficient to measure the vortices, it was confirmed that the boundary layer is laminar for the entire model. Measurements with suction also did not show the Görtler vortices.</div><div><br></div><div>Surface pressure fluctuations were measured on the flare. Apparent second-mode waves were detected. The suction measurements showed a slight increase in second-mode peak frequency over the baseline results, as expected.</div><div><br></div><div>Concerns had been raised about acoustic noise that might be radiated from the suction section. Thus, fluctuations above the suction section were measured using a pitot probe and using focused-laser differential interferometry. The measurements during suction showed no noticeable increase in fluctuations compared to the baseline results.</div>

The primary function of an automobile rear View Mirror is to provide the driver with a clear vision interpretation of all objects to the rear and side of the vehicle. The rear View Mirror is a bluff body and there are several problems associated with the rear View Mirror. These include buffeting, image distortion (due to aerodynamically induced and structural vibration), aerodynamically induced noise (due to cavities and gaps) and water and dirt accumulation on Mirror glass Surface. Due to excessive glass vibration, the rear View Mirror may not provide a clear image. Thus, vibrations of Mirror can severely impair the driver's vision and safety of the vehicle and its occupants. The rear View Mirrors are generally located close to the A-pillar region on the side window. A conical vortex forms on the side window close to A-pillar due to A-pillar geometry and the presence of side rear View Mirror and flow separation from it makes the airflow even more complex. The primary objective of this work is to study the aerodynamic pressures on Mirror Surface at Various speeds to determine the effects of aerodynamics on to Mirror vibration. Additionally, the Mirror was modified by Shrouding around the external periphery to determine the possibility of minimisation of aerodynamic pressure fluctuations and thereby vibration. The Shrouding length used for the analysis was of 24mm, 34mm and 44mm length. The mean and fluctuating pressures were measured using a production rear side View Mirror fitted to a ¼ quarter production passenger car in RMIT Industrial Wind Tunnel. The tests were also conducted in semi-isolation condition to understand influence of the A-pillar geometry. The mean and fluctuating pressures were converted into non-dimensional pressure coefficients (Cp and Cprms) and the frequency content of the fluctuating pressure was analysed. The results show that the fluctuating aerodynamic pressures are not uniformly distributed over an automobile Mirror Surface. The highest magnitude of fluctuating pressure for the standard Mirror was found at the central bottom part of the Mirror Surface. The highest magnitude of fluctuating pressure for the modified Mirror was found at the central top part of the Mirror Surface. As expected, the modification has significant effect on the magnitude of fluctuating pressure. The results show that an increase of Shrouding length reduces the magnitude of the fluctuating pressure. The frequency-based analysis was done to understand the energy characteristics of the flow, particularly to its phase, since it is the out of phase components that usually cause Mirror rotational vibration. The spectral analysis showed that the magnitude of the energy distribution reduces with increase of shrouding length throughout the frequency range. Flow visualisation was also used to supplement the pressure data. The effects of yaw angles were not included in this study, however, are thought to be worthy of further investigation. On road testing and the variation of mirror locations might have some effects on the fluctuating pressures. These need to be investigated in the future work. The quarter model used in this study was a car specific. However, for more generic results, a simplified model with variable geometry can be used in future study.

This document addresses problems encountered when establishing the very low air-flow speeds required for experimental investigations of the mechanisms of low-Reynolds-number boundary-layer turbulence. Small-scale motions in the near-wall region are important features of turbulent boundary-layer dynamics, and, if these features are to be resolved by measurements in air with conventionally-sized hot-wire probes, a well-behaved canonical turbulent boundary layer must be developed at free stream flow speeds no higher than 4 m/s. However, at such low speeds, the turbulent boundary layers developed on the walls of a wind tunnel are very susceptible to perturbation by non-turbulent time-dependent flow structures which originate upstream from the test section in the laminar flow at the inlet and in the contraction. Four different non-turbulent flow structures have been identified. The first is a result of quasi-two-dimensional separation of the laminar boundary-layer from the surfaces of the wind-tunnel contraction. Potential flow simulations show that susceptibility to this form of separation is reduced by increasing the degree of axisymmetry in the cross-section geometry and by decreasing the streamwise curvature of the concave surfaces. The second source of time-dependence in the laminar boundary-layer flow is an array of weak streamwise vortices produced by Goertler instability. The Goertler vortices can be removed by boundary-layer suction at the contraction exit. The third form of flow perturbation, revealed by visualisation experiments with streamers, is a weak large-scale forced-vortex swirl produced by random spatial fluctuations of temperature at the wind-tunnel inlet. This can be prevented by thorough mixing of the inlet flow; for example, a centrifugal blower installed at the inlet reduces the amplitude of temperature nonuniformity by a factor of about forty and so prevents buoyancy-driven swirl. When subjected to weak pressure gradients near the start of a wind-tunnel contraction, Goertler vortices in laminar wall layers can develop into three-dimensional separations with strong counter-rotating trailing vortices. These trailing vortices are the fourth source of unsteady flow in the test-section. They can be suppressed by a series of appropriately located screens which remove the low-speed-streak precursors of the three-dimensional separations. Elimination of the above four contaminating secondary flows permits the development of a steady uniform downstream flow and well-behaved turbulent wall layers. Measurements of velocity in the turbulent boundary layer of the test-section have been obtained by hot-wire anemometry. When a hot-wire probe is located within the viscous sublayer, heat transfer from the hot-wire filament to the wall produces significant errors in the measurements of both the mean and the fluctuating velocity components. This error is known as wall-proximity effect and two successful methods are developed for removing it from the hot-wire signal. The first method is based on the observation that, if all experimental parameters except flow speed and distance from the wall are fixed, the velocity error may be expressed nondimensionally as a function of only one parameter, in the form DeltaU^+=f(y^+). The second method, which also accommodates the effect of changing the hot-wire overheat ratio, is based on a dimensional analyis of heat transfer to the wall. Velocity measurements in the turbulent boundary layer at the mid-plane of a nearly square test-section duct have established that, when the boundary-layer thickness is less than one quarter of the duct height, mean-velocity characteristics are indistinguishable from those of a two-dimensional flat-plate boundary layer. In thicker mid-plane boundary layers, the mean-velocity characteristics are affected by stress-induced secondary flow and by lateral constriction of the boundary-layer wake region. A significant difference between flat-plate and duct boundary layers is also observed in momentum-balance calculations. The momentum-integral equation for a duct requires definitions of momentumd and displacement thickness which are different from those given for flat-plate boundary layers. Momentum-thickness growth rates predicted by the momentum-integral equation for a duct agree closely with measurements of the newly defined duct momentum thickness. Such agreement cannot be obtained in terms of standard flat-plate momentum thickness. In duct boundary layers with Reynolds numbers Re_theta between 400 and 2600, similarity in the wake-region distributions of streamwise turbulence statistics has been obtained by normalising distance from the wall with the flat-plate momentum thickness, theta_2. This result indicates that, in contrast with the mean velocity characteristics, the structure of mid-plane turbulence does not depend on the proportion of duct cross-section occupied by boundary layers and is essentially the same as in a flat-plate boundary layer. For Reynolds numbers less than 400, both wall-region and wake-region similarity fail because near-wall turbulence events interact strongly with the free stream flow and because large scale turbulence motions are directly influenced by the wall. In these conditions, which exist in both duct and flat-plate turbulent boundary layers, there is no distinct near-wall or wake region, and the behaviour of turbulence throughout the boundary layer depends on both wall variables and on outer region variables simultaneously. / Thesis (Ph.D.)--School of Mechanical Engineering, 1998.