A crescente preocupação ambiental e a necessidade de se criar produtos mais eficientes têm impulsionado os pesquisadores a realizarem estudos acerca da aerodinâmica veicular. Estes dois fatores constituem os principais motivos, pelos quais existe uma grande procura por conhecimento nesta área. Esta ciência pode ser considerada relativamente nova e ainda carece de uma base de dados. Entender como a aerodinâmica se relaciona com o consumo de combustível nos automóveis, à medida que o arrasto impõe resistência ao deslocamento dos mesmos, é algo que tem estimulado as indústrias automotivas a investirem grandes esforços na obtenção de ferramentas, que possam representar as condições de tráfego normais e, assim conseguir prever o desempenho do produto em desenvolvimento. Os túneis de vento e a simulação computacional surgem neste ambiente como as principais ferramentas de análise e predição do escoamento ao redor do veículo. Por isso seu entendimento faz-se de extrema necessidade. Ter conhecimento sobre a concepção do seu projeto, como funcionam, seus pontos fortes e suas fraquezas, são requisitos necessários para a pessoa que deseja estudar esta ciência. O presente trabalho traz uma contextualização histórica da aerodinâmica veicular nas indústrias automotiva e automobilística, além de apresentar aspectos técnicos relacionados aos túneis de vento e simulação computacional. Abordando as vantagens e desvantagens de cada ferramenta, expõe-se o fato de que estas ferramentas são complementares no estudo aerodinâmico. Para exemplificar a utilização dessas ferramentas, foi realizado um estudo aerodinâmico sobre uma geometria básica, que representa com similaridade os veículos tipo hatchback, denominada Modelo SAE em ambiente computacional. Os conceitos acerca do arrasto veicular e estabilidade veicular foram expostos para embasar este estudo. Este modelo foi submetido a diferentes geometrias traseiras e condições de escoamento simétricas e assimétricas. Este estudo demonstrou que o arrasto e a estabilidade veicular compreendem conceitos distintos e, dessa forma, é possível diminuir o arrasto de um veículo sem haver perda de estabilidade. / The growing environmental concern and the necessity to create more efficient products have motivated researchers to conduct studies about the aerodynamic vehicle. These two aspects are the main reasons which are promoting a great demand for knowledge in this theme. This science may be considered relatively new and still lacks more databases. Understand how aerodynamics is related to automobiles fuel consumption such as drag resistance imposed to their displacement, is something that has made the automotive industries invest considerable effort in obtaining tools which may represent the normal traffic conditions and thus, able to predict the performance of the product in development stage. The wind tunnels and computer simulations appear in this environment as the main tools for analysis and prediction of the flow around vehicle. The understanding about them is so of utmost necessity. Knowing how it was designed, how they work, their strengths and weaknesses are essential requirements for the person who wants to study this science. This material presents a historical development of vehicle aerodynamics in automotive and motor-racing industries, indeed technical aspects related to wind tunnels and computational fluid dynamics. Exposing the advantages and disadvantages of both tools, it is evidenced these tools complement each other during an aerodynamic study. To exemplify these tools utility an aerodynamic research was conducted using a basic form geometry known as SAE Model that represents with similarity the hatchback vehicles in the market. Drag and vehicle stability concepts were exposed to build a solid basis for this study. This model was submitted to different rear geometries, symmetric and asymmetric flow conditions. It could be demonstrated that drag and vehicle stability have distinct concepts and therefore it is possible diminish the first without damaging the later.

Losses associated with turbulent flows dissipate a significant amount of generated energy. Such losses originate from the drag force, which is often described as the sum of the pressure drag and the friction drag. This thesis sets out to explore the hypothesis that passive wall motions driven by fluid mechanical forces are able to reduce the friction drag in fully developed turbulent boundary layers. Firstly, the streamwise and spanwise opposition controls proposed by Choi et al. (1994, Journal of Fluid Mechanics) are revisited to identify beneficial wall motions. Near-wall streamwise or spanwise velocity fluctuations are measured along a detection plane parallel to the wall (sensing). For streamwise control, the wall velocities are set to be equivalent to the measured streamwise velocity fluctuations, whereas for spanwise control, the wall velocities are set to have the same magnitude but opposite direction as the measured spanwise velocity fluctuations (actuation). Direct numerical simulations of canonical turbulent channel flows are carried out at low (Reτ ≈ 180) and intermediate (Reτ ≈ 1000) Reynolds numbers to quantify the effect of the distance between the wall and the detection plane. The investigation reveals the primary differences between the mechanisms underlying the two active in-plane controls. The modified flow features and turbulence statistics show that the streamwise control amplifies the most energetic streamwise velocity fluctuations and damps the near-wall vorticity fluctuations. In comparison, the spanwise control induces near-wall vorticity in order to counteract the quasi-streamwise vortices of the near-wall cycle and suppress turbulence production. Although, the working principles of the active controls are fundamentally different, both achieve drag reduction by mitigating momentum transfer between the velocity components. Secondly, two theoretical passive compliant wall models are proposed, the aim being to sustain beneficial wall motions identified by active flow control simulations. In the proposed models, streamwise or spanwise in-plane wall motions are governed by an array of independent one-degree-of-freedom damped harmonic oscillators. Unidirectional wall motions are driven by local streamwise or spanwise wall shear stresses. A weak coupling scheme is implemented to investigate the interaction between the compliant surface models and the turbulent flow in the channel by means of direct numerical simulations. A linear analytical solution of the coupled differential equation system is derived for laminar pulsatile channel flows allowing verification and validation of the numerical model. The obtained analytical solution is utilised to map the parameter space of the passive controls and estimate the effect of the wall motions. It is shown that depending on the control parameters, the proposed compliant walls decrease or increase the vorticity fluctuations at the wall similarly to the active controls. This is confirmed by direct numerical simulations. On the one hand, when the control parameters are chosen appropriately, the passive streamwise control damps the near-wall vorticity fluctuations and sustains the same drag reduction mechanism as the active streamwise control. This leads to modest, 3.7% and 2.3% drag reductions at low and intermediate Reynolds numbers. On the other hand, the spanwise passive control is not capable of increasing the near-wall vorticity fluctuations as dictated by the active spanwise control. For this reason, passive spanwise wall motions can increase the friction drag by more than 50%. The results emphasise the necessity of anisotropy for a practical compliant wall design. The present work demonstrates for the first time that passive wall motions can decrease friction drag in fully turbulent wall-bounded flows. The thesis sheds light on the working principle of an active streamwise control, and proposes a passive streamwise control exploiting the same drag reduction mechanism. An analytical model is developed to give a ready prediction of the statistical behaviour of passive in-plane wall motions. Whereas streamwise passive wall motions are found beneficial when the control parameters are chosen appropriately, solely spanwise passive wall motions lead to a drag penalty.

A crescente preocupação ambiental e a necessidade de se criar produtos mais eficientes têm impulsionado os pesquisadores a realizarem estudos acerca da aerodinâmica veicular. Estes dois fatores constituem os principais motivos, pelos quais existe uma grande procura por conhecimento nesta área. Esta ciência pode ser considerada relativamente nova e ainda carece de uma base de dados. Entender como a aerodinâmica se relaciona com o consumo de combustível nos automóveis, à medida que o arrasto impõe resistência ao deslocamento dos mesmos, é algo que tem estimulado as indústrias automotivas a investirem grandes esforços na obtenção de ferramentas, que possam representar as condições de tráfego normais e, assim conseguir prever o desempenho do produto em desenvolvimento. Os túneis de vento e a simulação computacional surgem neste ambiente como as principais ferramentas de análise e predição do escoamento ao redor do veículo. Por isso seu entendimento faz-se de extrema necessidade. Ter conhecimento sobre a concepção do seu projeto, como funcionam, seus pontos fortes e suas fraquezas, são requisitos necessários para a pessoa que deseja estudar esta ciência. O presente trabalho traz uma contextualização histórica da aerodinâmica veicular nas indústrias automotiva e automobilística, além de apresentar aspectos técnicos relacionados aos túneis de vento e simulação computacional. Abordando as vantagens e desvantagens de cada ferramenta, expõe-se o fato de que estas ferramentas são complementares no estudo aerodinâmico. Para exemplificar a utilização dessas ferramentas, foi realizado um estudo aerodinâmico sobre uma geometria básica, que representa com similaridade os veículos tipo hatchback, denominada Modelo SAE em ambiente computacional. Os conceitos acerca do arrasto veicular e estabilidade veicular foram expostos para embasar este estudo. Este modelo foi submetido a diferentes geometrias traseiras e condições de escoamento simétricas e assimétricas. Este estudo demonstrou que o arrasto e a estabilidade veicular compreendem conceitos distintos e, dessa forma, é possível diminuir o arrasto de um veículo sem haver perda de estabilidade. / The growing environmental concern and the necessity to create more efficient products have motivated researchers to conduct studies about the aerodynamic vehicle. These two aspects are the main reasons which are promoting a great demand for knowledge in this theme. This science may be considered relatively new and still lacks more databases. Understand how aerodynamics is related to automobiles fuel consumption such as drag resistance imposed to their displacement, is something that has made the automotive industries invest considerable effort in obtaining tools which may represent the normal traffic conditions and thus, able to predict the performance of the product in development stage. The wind tunnels and computer simulations appear in this environment as the main tools for analysis and prediction of the flow around vehicle. The understanding about them is so of utmost necessity. Knowing how it was designed, how they work, their strengths and weaknesses are essential requirements for the person who wants to study this science. This material presents a historical development of vehicle aerodynamics in automotive and motor-racing industries, indeed technical aspects related to wind tunnels and computational fluid dynamics. Exposing the advantages and disadvantages of both tools, it is evidenced these tools complement each other during an aerodynamic study. To exemplify these tools utility an aerodynamic research was conducted using a basic form geometry known as SAE Model that represents with similarity the hatchback vehicles in the market. Drag and vehicle stability concepts were exposed to build a solid basis for this study. This model was submitted to different rear geometries, symmetric and asymmetric flow conditions. It could be demonstrated that drag and vehicle stability have distinct concepts and therefore it is possible diminish the first without damaging the later.

There is a wide variety of tails, fins, scales, riblets and surface coatings, which are used by motile animals in nature. Since organisms currently living on earth have gone through millions of years of evolution, one can expect that their design is optimal for their tasks, including locomotion. However, the exterior of living animals has range of different functions, from camouflage to heat insulation; therefore it is a very challenging task to isolate mechanisms, which are beneficial to reduce the motion resistance of the body. There are two general categories of mechanisms existing in locomotion and flow control. The first is active flow control, when an organism is actively moving some parts or the whole body (exerts energy) in order to modify the surrounding flow field (for example, flapping bird wings). The second is passive flow control, in which an organism has an appendage or a coating, which is not actively controlled (no energy is spent), but is interacting with surrounding flow in a beneficial way. Our aim is to find novel mechanisms for passive flow control. We start by looking at a simple model of an appendage (splitter plate) behind a bluff body (circular cylinder). If a recirculation region forms behind the body, already in this simple system there is a symmetry breaking effect for sufficiently short plates, which passively generates turn and drift of the body. We have found that this effect is caused by the pressure forces in the recirculation region, which pushes the plate away from the vertical in a manner similar to how a straight inverted pendulum falls under the influence of gravity. In order to investigate this symmetry breaking, we developed an extension of the immersed boundary projection method, in which the rigid body dynamics and fluid dynamics are coupled implicitly. The method is capable of solving for particle motion in a fluid for very small density ratios. We also explain our findings by a simple yet quantitative reduced-order model and soap-film experiments. To extend our work, we investigate flow around bodies, which are coated by a porous and elastic material. We have analysed various theoretical approaches to modeling a coating in a continuous manner. We aim to solve the governing equations numerically. We have selected multi-scale expansion approach, of which we present some initial results. / Många djur använder sig av fjäll, päls, hår eller fjädrar för att öka sin förmåga att förflytta sig i luft eller vatten. Evolutionen har främjat ojämna, sträva eller gropiga ytor, vilka har en tendens att minska det totala motståndet som uppstår när en kropp rör sig i vatten eller luft, jämfört med en helt slät och jämn yta.Det finns två kategorier av metoder för manipulering av strömning (så kallad flödeskontroll). Den första är en aktiv metod, där organismer aktivt rör hela eller delar av kroppen (förbrukar energi) för att manipulera omgivande strömningsfält. Den andra metoden är passiv, där organismer har utväxter eller ytbeläggningar som de inte är aktivt har kontroll över (ingen energi förbrukas), men som samverkar med omgivande strömningsfält på ett fördelaktigt sätt. Vårt mål är att hitta nya mekanismer för passiv flödeskontroll.Vi börjar med att studera en enkel modell för hur en utväxt samverkar med en strömmande fluid genom att fästa en platta på en cirkulär cylinder. Om en vak (så-kallad återcirkulationsregion) bildas bakom kroppen, bryts symmetrin i strömningsfältet då plattan är tillräckligt kort. Som en konsekvens av detta roterar kroppen och driver i sidled. Vi visar att detta fenomen orsakas av tryckkrafter i återcirkulationsregionen, som förskjuter plattan från dess vertikala läge. Vi argumenterar att denna mekanism är samma mekanism som får en inverterad pendel att falla under inverkan av gravitation. För att analysera symmetribrytningen, utvecklade vi en numerisk metod (immersed boundary projection method), som implicit kopplar stelkropps- och strömningsdynamik. Med hjälp av denna metod kan vi simulera partiklar i fluider med väldigt låga densitetsskillnader. Våra resultat förklaras även med hjälp av en enkel modell av låg ordning och med hjälp av såphinneexperiment.Som nästa steg i vårt arbete, ämnar vi att studera strömningen kring kroppar som är belagda av tät, porös och elastisk beläggning. Vi har analyserat möjliga tillvägagångssätt för att modellera beläggningar med kontinuumteori. Vi har valt en metod baserad på en flerskalig expansionsmetod, från vilken vi presenterar våra preliminära resultat. / <p>QC 20150119</p>

Rising fuel cost has motivated increased fuel efficiency for freight trains. At cruising speed,the largest contributing factor to the fuel consumption is aerodynamic drag. As a result of stagnationand flow separation on and around lead and trailing cars, the first and last railcars experiencegreater drag than intermediate cars. Accordingly, this work focused on reducing drag on lead locomotivesby designing and optimizing an add-on nose fairing that is feasible for industrial operation.The fairing shape design was performed via computational fluid dynamic (CFD) software.The simulations consisted of two in-line freight locomotives, a stretch of rails on a raised subgrade,a computational domain, and a unique fairing geometry that was attached to the lead locomotive ineach non-baseline case. Relative motion was simulated by fixing the train and translating the rails,subgrade, and ground at a constant velocity. An equivalent uniform inlet velocity was applied atzero degree yaw to simulate relative motion between the air and the train.Five fairing families-Fairing Families A-E (FFA-FFE)-are presented in this thesis.Multidimensional regressions are created for each family to approximate drag as a function ofthe design variables. Thus, railroad companies may choose an alternative fairing if the recommendedfairing does not meet their needs and still have a performance estimate. The regression forFFE is used as a surrogate model in a surrogate based optimization. Results from a wind tunneltest and from CFD are reported on an FFE geometry to validate the CFD model. The wind tunneltest predicts a nominal drag reduction of 16%, and the CFD model predicts a reduction of 17%.A qualitative analysis is performed on the simulations containing the baseline locomotive, the optimalfairings from FFA-FFC, and the hybrid child and parent geometries from FFA & FFC. Theanalysis reveals that optimal performance is achieved for a narrow geometry from FFC becausesuction behind the fairing is greatly reduced. Similarly, the analysis reveals that concave geometriesboost the flow over the top leading edge of the locomotive, thus eliminating a vortex upstreamof the windshields. As a result, concave geometries yield greater reductions in drag.The design variable definitions for each family were strategically selected to improve manufacturability,operational safety, and aerodynamic performance relative to the previous families.As a result, the optimal geometry from FFE is believed to most completely satisfy the constraintsof the design problem and should be given the most consideration for application in the railroadindustry. The CFD solution for this particular geometry suggests a nominal drag reduction of 17%on the lead locomotive in an industrial freight train.