O escoamento em torno de corpos tem sido objeto de estudo de muitos pesquisadores e é muito explorado experimental e computacionalmente, devido a sua grande aplicabilidade na engenharia. No entanto, simular computacionalmente este tipo de escoamento requer uma atenção especial ao escolher o tipo malha a ser utilizado. Em muitos casos faz-se necessário o uso de uma malha que se adapte ao contorno do obstáculo, o que pode ocasionar um aumento no esforço computacional. Um maneira de contornar este problema é a utilização do Método das Fronteiras Imersas, que possibilita o uso de malha cartesiana na simulação computacional do escoamento em torno de obstáculos. Isso é possível através da adição de um termo forçante nas equações que modelam o escoamento, e assim as forças que agem sobre o contorno do corpo são transferidas diretamente para a malha. O objetivo deste trabalho de mestrado foi implementar o método das Fronteiras Imersas e simular o escoamento em torno de um cilindro circular em repouso, movimentando-se na mesma direção do escoamento, na direção perpendicular ao escoamento, ou rotacionando em torno do próprio eixo. As simulações computacionais possibilitaram a captura do fenômeno de Atrelagem Síncrona, caracterizado pela sincronia entre a frequência de desprendimento natural de vórtices e a frequência de oscilação do mesmo. O Método das Fronteiras Imersas mostrou um ótimo desempenho quando comparado a resultados experimentais e numéricos encontrados na literatura / The flow around bodies have been studied by many researchers. Both experimental and computational approaches have been extensively explored in researches on flow around bodies and have been applied in many engeneering problems. However, to choose an appropriate type of mesh to perform computational simulations of this type of problem requires special attention. In many cases, it is necessary to use a mesh that is able to conform to the boundary if a given obstacle. The need to perform this adaptation may increase the computational effort. The Immersed Boundary Method enables the use of cartesian meshes to perform computational simulations of flows around obstacles. The idea of this method is to add a forcing term in the equations that model the flow. Thus, the forces applied on the body boundaries are directly transfered to the mesh. The aim of this work was to perform a computational implementation of the Immersed Boundary Method to simulate the flow over a oscilating circular cylinder. This oscilation may be inline with the flow, cross-flow, or rotating. The computational simulations enabled the capture of the lock-in phenomena, which consists of the syncronization between the vortex shedding frequency and the cylinder oscilation frequency. The results obtained from the computational simulations using the Immersed Boundary Method were in good agreement with the numerical and experimental results found in the literature

The aerodynamic performance of low aspect ratio wings at low Reynolds numbers applicable to micro air vehicle design was studied in this thesis. There is an overall lack of data for this low Reynolds number range, particularly concerning details of local flow behavior along the span. Experiments were conducted to measure the local pressure distributions on a wing at various spanwise locations in a Reynolds number range 30000 < Re < 90000. The model wing consisted of numerous wing sections and had a rectangular planform with NACA0012 airfoil shape with aspect ratio of one. One wing section, with pressure ports at various chordwise locations, was placed at different spanwise locations on a wing to effectively obtain the local pressure information. Integration of the pressure distributions yielded the local lift coefficients. Comparison of the local lift distributions to optimal elliptic lift distribution was conducted. This comparison showed a sharply peaked lift distribution near the wing tip resulting in a drastic deviation from the equivalent elliptic lift distributions predicted by the finite wing theory. The local lift distributions were further analyzed to determine the total lift coefficients vs angle of attack curves, span efficiency factors and the induced drag coefficients. Measured span efficiency factors, which were lower than predictions of the elliptic wing theory, can be understood by studying deviations of measured lift from the elliptic lift distribution. We conclude that elliptic wing theory is not sufficient to predict these aerodynamic performance parameters. Overall, these local measurements provided a better understanding of the low Reynolds number aerodynamics of the low aspect ratio wings.

O presente trabalho apresenta uma metodologia de simulação numérica de perfis aerodinâmicos bidimensionais com foco na utilização para o projeto e otimização de pás e rotores de pequenas turbinas eólicas de eixo horizontal, bem como o emprego desses métodos em simulações nas quais efeitos de alta solidez do rotor e baixos números de Reynolds são avaliados. Essa metodologia inclui geração de malhas, seleção de métodos numéricos e validação, tendo as escolhas sido guiadas pelas práticas mais bem sucedidas na simulação de perfis aerodinâmicos, e foi aplicada na simulação dos aerofólios NACA 0012, S809 e SD7062. O código comercial ANSYS Fluent foi utilizado em todas as simulações. Na simulação de aerofólios isolados a altos números de Reynolds dos perfis NACA 0012 e S809, o modelo Transition SST (γ-Reθ) apresentou resultados mais próximos a dados experimentais do que aqueles apresentados pelo modelo k-ω SST para CL e CD, além de produzir resultados para CP que mostraram boa precisão quando comparados aos mesmos dados experimentais. Resultados de CL, CD, CF e CP são apresentados para 20 diferentes condições de operação às quais o perfil SD7062 foi submetido, com números de Reynolds variando entre 25.000 e 125.000. As distribuições dos dois últimos coeficientes sobre os dorsos do aerofólio evidenciam com clareza a presença e magnitude da bolha de separação laminar. Os coeficientes de sustentação e arrasto mostram o impacto negativo da presença da bolha nessa faixa de números de Reynolds. Além disso, nos casos simulados, o arrasto aumenta em função da diminuição do Re. Um design de pá produzido com o auxílio do código de otimização SWRDC, baseado em algoritmos genéticos, é apresentado. Três seções ao longo da envergadura dessa pá foram simuladas em uma bateria de 45 simulações, sob diversas condições de operação em função de solidez, ângulo de ataque e razão de velocidade de ponta de pá. Esses resultados mostram que a bolha de separação laminar se move na direção do bordo de ataque com o aumento da solidez, do ângulo de ataque e da TSR. Além disso, distribuições do CP mostram aumento de pressão em ambos os dorsos do perfil quando submetido aos efeitos da solidez, embora esses efeitos tenham sido responsáveis por um aumento na relação CL/CD nos casos estudados. / This thesis presents a methodology of two-dimensional airfoil simulation focusing on its application on the design and optimization of blades and rotors of small horizontal axis wind turbines, and its application in a set of numerical simulations involving high rotor solidity and low-Re effects. This methodology includes grid generation, selection of numerical methods and validation, reflecting the most successful practices in airfoil simulation, and was applied in the simulation of the NACA 0012, S809 and SD7062 airfoils. The ANSYS Fluent commercial code was used in all simulations. Results for the isolated NACA 0012 and S809 airfoils at high Reynolds numbers show that the Transition SST (γ-Reθ) turbulence model produces results closer to experimental data than those yielded by the SST k-ω model for CL and CD, having also produced CP plots that show good agreement to the same experimental data. Plots of CL, CD, CF and CP for the SD7062 airfoil are presented, for simulations at 20 different operating conditions. The CF and CP distributions evidence the negative impact of the laminar separation bubble in the range of Reynolds numbers evaluated. Results show that, for Re between 25,000 and 125,000, drag increases with decreasing Re. A blade design generated using the SWRDC optimization code, based on genetic algorithms, is presented. Three sections of the resulting blade shape were selected and were tested in a set of 45 simulations, under an array of operating conditions defined by solidity, angle of attack and TSR. Results show that the laminar separation bubble moves towards the leading edge with increasing solidity, angle of attack and TSR. Furthermore, CP plots show an increase in pressure on both surfaces when the airfoil is subject to solidity effects, although these effects show an increase in the lift-to-drag ratio at the conditions evaluated.

A l’heure actuelle, la microfluidique est une science en plein développement ayant un besoin croissant de dispositifs permettant de générer des écoulements aux échelles micrométriques. Les phénomènes physiques mis en jeu lors du mouvement d’un fluide sont en effet majoritairement gouvernés par la viscosité (bas nombre de Reynolds) contrairement aux écoulements macroscopiques dominés par les effets inertiels.Dans cette thèse, les écoulements engendrés par le mouvement de parois mobiles ont été étudiés en vue d’une application aux micropompes, dispositifs essentiels en microfluidique.Dans une première partie, une étude analytique et numérique évalue la possibilité de générer un écoulement par un cylindre en rotation à proximité de parois mobiles.Les résultats obtenus du régime de Stokes (Re=0) jusqu’à un nombre de Reynolds Re=60 en régime stationnaire témoignent du potentiel notable d’intégration de cette géométrie dans les microsystèmes en tant que micropompes.Dans une seconde partie, une micropompe, basée sur un principe de fonctionnement novateur, est conçue par l’intermédiaire des techniques de microfabrication. Dans cette optique, le procédé de gravure RIE d’un élastomère est entièrement développé. Les performances de la micropompe en terme de pression et débit générés dépassent l’état de l’art des microsystèmes similaires et ceci en utilisant une technologie simple et bas-coût / Currently, microfluidic is a science field in constant development with an increasing need of devices able to generate flows at the micrometer order. At these length scales, physical phenomenons occurring in a moving fluid are mainly governed by its viscosity (low Reynolds number) contrary to macroscale flows dominated by inertial effects.In this thesis, a study on flows engendered by moving walls has been carried to fulfill to micropumps devices.In a first part, an analytical and a numerical study evaluates the possibility to generate a flow for a rotating cylinder close to moving boundaries.The results ranging from Stokes flows (Re=0) up to the low Reynolds number Re=60 in the stationary regime reveals the noticeable potential of integrating this device in microsystems as a micropump. In a second part, a new micropump, based on an innovative principle, is designed thanks to microfabrication technologies. In this perspective, the etching process of an elastomer called Silastic S is developed. Micropump performances in terms of pressure and flow rate are beyond the state of the art for similar microsystems and are achieved by using a simple and low-cost technology

At low Reynolds number flows, the effect of inertia becomes negligible and the fluid motion is dominated by the effect of viscous forces. Understanding of the behaviour of low Reynolds number flows underpins the prediction of the motion of microorganisms and particle sedimentation as well as the development of micro-robots that could potentially swim inside the human body to perform targeted drug/cell delivery and non-invasive microsurgery. The work in this thesis focuses on developing an understanding in the mathematical analysis of objects moving at low Reynolds numbers. A boundary element implementation of the Method of regularized Stokeslets (MRS) is applied to analyse the low Reynolds number flow field around an object of simple shape (sphere and cube). It also showed that the results obtained by a boundary element implementation for an unbounded cube, where singularities are presented in the corners of the cube, agrees with more complex solutions methods such as a GBEM and FEM.A methodology for analysing the effect of walls by locating collocation points on the surface of the walls and the object is presented. First at all, this methodology is validated with a boundary element implementation of the method of images for a sphere at different locations. Then, the method is extended when more than one wall is presented. This methodology is applied to predict the velocity filed of a cube moving in a tow tank at low Reynolds numbers for two different cases with a supporting rod similar to an experimental set-up, and without the supporting rod as in the CFD simulations based on the FVM. The results indicate a good match between CFD and the MRS, and an excellent approximation between the MRS and experimental data from PIV measurements. The drag, thrust and torque generated by helices moving at low Reynolds numbers in an unbounded medium is analysed by the resistive force theory, a slender body theory, and a boundary element method of the MRS. The results show that the resistive force theory predict accurately the drag, thrust and torque of moving helices when the resistive force coefficients are calculated from a slender body theory approximation by calculating independently the resistive force coefficients for translation and rotation, because it is observed that the resistive force coefficients depend also of the nature of motion. Moreover, the thrust generated by helices of different pitch angles is analysed calculated by a CFD numerical simulation based on the FVM and a boundary element implementation, an compared with experimental data. The results also show an excellent prediction between the boundary element implementation, the CFD results and the experimental data. Finally, a boundary element implementation of the MRS is applied to predict swimming of a biomimetic swimmer that mimics the motion of E.coli bacteria in an unbounded medium. The results are compared with the propulsive velocity and induced angular velocity measurement by recording the motion of the biomimetic swimmer in a square tank. It is observed that special care needs to be taken when the biomimetic swimmer is modelled inside the tank, as there is an apparent increment in the calculate thrust propulsion which does not represent a real situation of the biometic swimmer which propels by a power supply. However, this increment does not represent the condition of the biomimetic swimmer and a suggested methodology based on the solution from an unbounded case and when the swimmer is moving inside the tank is presented. In addition, the prediction of the free-swimming velocity for the biomimetic swimmer agrees with the results obtained by the MRS when the resistive force coefficients are calculated from a SBT implementation. The results obtained in this work have showed that a boundary element implementation of the MRS produces results comparable with more complex numerical implementations such as GBEM, FEM, FVM, and also an excellent agreement with results obtained from experimentation. Therefore, it is a suitable and easy to apply methodology to analyse the motion of swimmers at low Reynolds numbers, such as the biomimetic swimmer modelled in this work.

Ce travail de thèse s’inscrit dans la grande problématique de la récupération d’énergie. Il s’agit plus précisément de convertir de petites quantités d’énergie cinétique présentes dans un écoulement d’air en énergie électrique par l’intermédiaire d’un convertisseur électrostatique. L’énergie électrique convertie est ensuite destinée à alimenter des capteurs autonomes communicants pour le monitoring de structures, le suivi environnemental, le monitoring de santé…Le manuscrit comprend une étude des travaux antérieurs en récupération d’énergie des écoulements d’air, la compréhension physique des phénomènes de conversion électrostatique, de mécanique des fluides et d’aérodynamique à très faibles nombres de Reynolds, ainsi qu’une description des prototypes développés et des résultats expérimentaux obtenus.Les récupérateurs que nous avons développés se divisent en deux grandes catégories : (i) les récupérateurs rotatifs qui transforment l’énergie cinétique de l’air en énergie mécanique de rotation et (ii) les récupérateurs aéroélastiques qui puisent l’énergie cinétique du vent pour produire de l’énergie mécanique par oscillations périodiques. Ces deux types de récupérateurs ont été associés à des convertisseurs électrostatiques dédiés, polarisés par l’ajout d’électrets ou auto-polarisés par triboélectricité. Les récupérateurs d'énergie ont été optimisés et nous avons notamment montré l'intérêt de la conversion électrostatique pour des dispositifs de petites dimensions (quelques cm²) fonctionnant à faible vitesse (<3m/s). Les densités surfaciques de puissance atteignent 5µW/cm2@1m/s pour les récupérateurs rotatifs et de l'ordre de 10µW/cm2@10m/s pour les récupérateurs aéroélastiques. Les micro-générateurs ont finalement été combinés à des circuits de gestion d'énergie pour alimenter des capteurs autonomes communicants, validant la chaine complète de récupération d'énergie, montrant par la même occasion l'intérêt des circuits de gestion d'énergie actifs de type SECE (synchronous electric charge extraction) ou MPP (maximum power point). / This work is enshrined in the energy harvesting context. More specifically, the purpose is to convert small amounts of kinetic energy from airflows into electrical energy through an electrostatic converter. The electrical energy produced is then intended to supply low power sensors for structural health monitoring, environmental follow-up, human monitoring…The manuscript includes an overview of the state of the art on airflow energy harvesting, the physical understanding of electrostatic conversion phenomena, fluid mechanics, ultra-low Reynolds number aerodynamics, a description of the prototypes developed and the results obtained.The harvesters we have developed are divided into two families: (i) the rotational harvesters which transform the kinetic energy of airflows into mechanical energy of rotation and (ii) the aeroelastic harvesters which use wind energy to produce mechanical energy of periodical oscillations. These two types of harvesters have been associated to different electrostatic converters, polarized by the addition of electrets or self-polarized by triboelectricity. The energy harvesters have been optimized and we have demonstrated the benefit of the electrostatic conversion for small devices (a few cm2) operating at low speeds (<3m/s). The power densities reach 5µW/cm2@1m/s for rotational devices and in the range of 10µW/cm2@10m/s for aeroelastic devices. The micro-generators were finally combined with power management circuits to supply autonomous and communicating sensors. This last stage completes the energy harvesting chain and also shows the high benefit of active circuits (synchronous electric charge extraction, maximum power point).

The vision driving the work reported herein is to investigate the fluid-structure interac-tion (FSI) effects of the flexible laminated blades for tilt-body micro-air-vehicles (MAV)proprotors in hover and forward flight configurations. This is in order to exploit the po-tential of flexible-bladed proprotor over the rigid-bladed proprotor in the enhancementof proprotor performance during hovering and cruising at a target forward speed. Forthat, the FSI model taking into account the specific problems devoted to MAV-sizedproprotor made of laminate composite was developed. The FSI model combines aerody-namic model adapting Blade Element Momentum (BEM) theory and structural modeladapting Anisotropic Finite Element Beam (AFEM) theory. The aerodynamic model isdeveloped to be capable of adapting in the analysis on low Reynolds number proprotors.In the structural model, the blade is modeled as an elastic beam undergoing deflectionsin flap, lag, and torsion to capture the coupling effects in anisotropic materials, adaptsthe structural analysis on proprotor blades made of laminate composite. The reliabilityof the developed FSI model is verified through a validation on both aerodynamic andstructural models, separately, on several MAV-sized proprotors. As for a direction to theanalysis on passively-adaptive proprotor blades, an optimal design on actively-adaptiveproprotor was carried out. For this, a program for designing the optimum rigid blades atsingle-point (for either isolated cruise-point or isolated hover-point) and multiple-point(combined cruise and hover point) for proprotors have been developed. The proceduresin the optimal design program employs the numerical iterative inverse design method,based upon the minimum thrust induced losses (MIL). Even if the work in this thesiswas directed primarily towards the proprotor, however, the propulsion system from themotor part was not neglected since the propulsion efficiency is a crucial factor to the suc-cess of MAVs. A cheap and time-effective method of proposing the best motor from theselected commercial motors was developed, based on Taguchi’s method. The sensitivityof the total power consumption to the variation of value of each motor design variableswas also studied. The benefit of the use of tip body in the blade and the effect of bendingon the induced twist and on the thrust degradation, respectively, were also analyzed andidentified. Finally, the systematically designed passively-adaptive composite proprotors were evaluated under steady operating conditions. Hovering and cruise propulsive performance, characterized by total power Ptotal, were compared between the rigid-bladed and flexible-bladed proprotors. As a result of the comparison, the flexible-bladed proprotor with fixed system is found to be capable of slightly enhancing the performance through the reduction in Ptotal over its optimal rigid-bladed proprotor. / L’idée principale du travail rapporté ici est d’étudier les effets de l’intéraction fluide-structure (FSI) de pales laminées flexibles pour les proprotors de micro véhicules aériens(MAV) de type tilt-body dans les configurations de vol stationnaire et en avant. Eneffet, le but est d’exploiter les possibilités offertes par les proprotors à pales flexiblespar rapport aux proprotors à pales rigides pour améliorer leur performance dans cesphases de vol. Le modèle FSI a été développé à cet effet. Ce modèle tient compte desproblèmes spécifiques liés aux proprotors de MAV faits de composite laminé. Il com-bine l’adaptation de modèle aérodynamique par la théorie d’élement de pale (BEM) etl’adaptation de modèle structurel par la théorie des éléments finis de poutre anisotropes(AFEM). Le modèle aérodynamique est développé pour être capable de s’adapter àl’analyse des proprotors à bas nombres de Reynolds. Dans le modèle structural, la paleest modélisée comme une poutre élastique subissant des déviations dans la flexion, latraction et la torsion afin de capturer les effets de couplage de matériaux anisotropes.Il adapte l’analyse structurale des pales du proprotor faites de composite laminé. Lafiabilité du modèle FSI développé est vérifiée à travers une validation par modèles aéro-dynamique et structural, séparément, sur plusieurs proprotors de MAV. Afin de se dirigervers une analyse de pales de proprotors à adaptation passive , une recherche de designoptimal a été effectuée pour des proprotor à adaptation active. Pour cela, un programmepour la conception de pales rigides optimales à un unique point de fonctionnement (soitle vol de croisière soit le vol stationnaire) et à plusieurs points (combinant croisière etvol stationnaire) ont été développés. Les procédures du programme de design optimalemploient les mèthodes de design inverse par itération numérique, sur la base de pertesde poussée induites minimales (MIL). Même si le travail dans cette thèse a été dirigéprincipalement vers le proprotor, la partie moteur du système de propulsion n’a pasété négligée puisque l’efficacité de la propulsion est un facteur crucial pour le succès desMAVs. Une méthode simple et rapide de sélection du meilleur moteur parmi les moteurscommerciaux choisis est élaborée sur la base de la méthode de Taguchi. La sensibilitéde la consommation d’énergie totale à la variation de la valeur de chaque variable deconception du moteur a été étudiée. Le bénéfice de l’utilisation de la charge à la pointe de la pale et l’effet de la flexion sur la torsion induite et sur la dégradation de la poussée respectivement ont aussi été analysés et identifiés. Enfin, les proprotors à pales flexibles conçues systématiquement ont été évalués dans des conditions de fonctionnement stables. Performances en vol stationnaire et performances croisière propulsive, caractérisées par la puissance totale Ptotal ont été comparées entre les proprotors à pales rigides et à pales flexibles. En tant que résultat de la comparaison, les proprotors à pales flexibles s’avère capable d’améliorer légèrement les performances par la réduction de la Ptotal surson optimal proprotors à pales rigides.

Nous avons tou(te)s été témoins des nuages d'étourneaux dans le ciel ou de la formation de bancs de poissons dans l'océan. Ce type d'organisation chez les êtres vivant se produit aussi à des échelles parfois invisibles pour l'oeil humain: celles des micro-organismes. Les suspensions de micro-nageurs présentent une dynamique riche. Elles peuvent former des structures cohérentes résultant d'un mouvement collectif, mélanger le fluides environnant et/ou modifier ses propriétés rhéologiques. Leurs comportements peuvent jouer un rôle important dans la survie, l'équilibre des espèces, leur stratégie trophique et même pour la fertilité animale. La diversité des phénomènes observés résulte de l'interaction complexe entre mécanismes de nage, processus physiologiques, processus chimiques et interactions hydrodynamiques. Comprendre et maîtriser les mécanismes impliqués fait nécessairement appel la Mécanique des Fluides. Les études expérimentales permettent de mettre en exergue certains phénomènes et parfois de les expliquer. Cependant la modélisation s'avère indispensable. Or, inclure une description fine des mécanismes de nages dans une suspension contenant des milliers (voire des millions) d'individus, implique de considérer une vaste gamme d'échelles couplées (typiquement du micron 10^-6m au millimètre 10^-3m). Décrire une physique multi-échelles pour ce type problème reste un défi majeur pour la modélisation numérique actuelle. Ainsi, dans le cadre de cette thèse nous nous proposons d'apporter une contribution dans cette direction. Nous montrerons dans une premiere partie qu'il est possible de reproduire les mécanismes de nage de façon satisfaisante à l'échelle du micro-organisme avec des modèles de différentes complexités. Nous présenterons ensuite nos développements pour étendre ces modèles a l'échelle de la suspension. Nous montrerons comment inclure simultanément les effets Browniens qui agissent sur les plus petite particules (10^-6m). Enfin, nous exploiterons l'outil mis en place pour simuler des suspensions actives. Sa capacité à reproduire certains résultats de la littérature à précision égale, à moindre coût et à plus grande échelle, permet de combler le fossé entre modèles individuels, travaux expérimentaux et modèles continus issus de la théorie cinétique. Forts de cet outil, nous tenterons de répondre à deux questions ouvertes dans la littérature expérimentale : l'origine des corrélations d'orientation dans les suspensions de microgouttes auto-propulsées et les mécanismes en jeu dans la diffusion des particules Browniennes dans les suspensions actives. / We have all witnessed the flocking of starlings in the sky and the schools of fish that form in the ocean. This kind of organization of living creatures is not limited to those that we see, but also occurs for those that we don’t : swimming microorganisms. Suspen- sions of micro-swimmers exhibit a rich dynamics. Their behaviors can play an important role in the survival of the group, its development, the balance between species, their trophic strategies and even animal fertility. They can form coherent structures due to collective motion, mix the surrounding fluid or modify its rheological properties. Such diversity results from the complex interplay between swimming strategies, physiological processes, chemical reactions and hydrodynamic interactions. Fluid Mechanics is there- fore essential to understand and master the mechanisms involved in these phenomena. While experimental studies bring out new findings and, sometimes, provide physical ex- planations, modeling remains essential. Yet, including an accurate description of the micro-swimmers in a suspension containing thousands (nay millions) individuals, requires considering a wide range of coupled scales (from one micron 10^−6m to several millimeters 10^−3m). What happens on large scales depends on sophisticated mechanisms occurring two or three orders of magnitude below. Therefore, the multiscale modeling of such phenomena is still a major challenge for the state-of-the-art numerical methods. This thesis aims at providing a contribution in that direction. In a first part, we will show that reproducing swimming mechanisms at the scale of the micro-swimmer can be achieved with various models spanning different levels of complexity. We will then present our developments to incorporate these models in an efficient framework for large scale simulations. We will show how to simultaneously account for the Brownian motion of the smallest particles (10^−6m). Our code reproduces known results from the literature with the same accuracy, but at lower cost and at larger scales, thus bridging a gap between particle-based models, experiments and continuum formulations from kinetic theory. Using the capabilities afforded by our method, we eventually address two open problems in the experimental literature : the origins of orientational correla- tions between interacting self-propelled micro-droplets and the mechanisms at play in the nonlinear enhancement of Brownian particle diffusion in active suspensions.

O presente trabalho apresenta uma metodologia de simulação numérica de perfis aerodinâmicos bidimensionais com foco na utilização para o projeto e otimização de pás e rotores de pequenas turbinas eólicas de eixo horizontal, bem como o emprego desses métodos em simulações nas quais efeitos de alta solidez do rotor e baixos números de Reynolds são avaliados. Essa metodologia inclui geração de malhas, seleção de métodos numéricos e validação, tendo as escolhas sido guiadas pelas práticas mais bem sucedidas na simulação de perfis aerodinâmicos, e foi aplicada na simulação dos aerofólios NACA 0012, S809 e SD7062. O código comercial ANSYS Fluent foi utilizado em todas as simulações. Na simulação de aerofólios isolados a altos números de Reynolds dos perfis NACA 0012 e S809, o modelo Transition SST (γ-Reθ) apresentou resultados mais próximos a dados experimentais do que aqueles apresentados pelo modelo k-ω SST para CL e CD, além de produzir resultados para CP que mostraram boa precisão quando comparados aos mesmos dados experimentais. Resultados de CL, CD, CF e CP são apresentados para 20 diferentes condições de operação às quais o perfil SD7062 foi submetido, com números de Reynolds variando entre 25.000 e 125.000. As distribuições dos dois últimos coeficientes sobre os dorsos do aerofólio evidenciam com clareza a presença e magnitude da bolha de separação laminar. Os coeficientes de sustentação e arrasto mostram o impacto negativo da presença da bolha nessa faixa de números de Reynolds. Além disso, nos casos simulados, o arrasto aumenta em função da diminuição do Re. Um design de pá produzido com o auxílio do código de otimização SWRDC, baseado em algoritmos genéticos, é apresentado. Três seções ao longo da envergadura dessa pá foram simuladas em uma bateria de 45 simulações, sob diversas condições de operação em função de solidez, ângulo de ataque e razão de velocidade de ponta de pá. Esses resultados mostram que a bolha de separação laminar se move na direção do bordo de ataque com o aumento da solidez, do ângulo de ataque e da TSR. Além disso, distribuições do CP mostram aumento de pressão em ambos os dorsos do perfil quando submetido aos efeitos da solidez, embora esses efeitos tenham sido responsáveis por um aumento na relação CL/CD nos casos estudados. / This thesis presents a methodology of two-dimensional airfoil simulation focusing on its application on the design and optimization of blades and rotors of small horizontal axis wind turbines, and its application in a set of numerical simulations involving high rotor solidity and low-Re effects. This methodology includes grid generation, selection of numerical methods and validation, reflecting the most successful practices in airfoil simulation, and was applied in the simulation of the NACA 0012, S809 and SD7062 airfoils. The ANSYS Fluent commercial code was used in all simulations. Results for the isolated NACA 0012 and S809 airfoils at high Reynolds numbers show that the Transition SST (γ-Reθ) turbulence model produces results closer to experimental data than those yielded by the SST k-ω model for CL and CD, having also produced CP plots that show good agreement to the same experimental data. Plots of CL, CD, CF and CP for the SD7062 airfoil are presented, for simulations at 20 different operating conditions. The CF and CP distributions evidence the negative impact of the laminar separation bubble in the range of Reynolds numbers evaluated. Results show that, for Re between 25,000 and 125,000, drag increases with decreasing Re. A blade design generated using the SWRDC optimization code, based on genetic algorithms, is presented. Three sections of the resulting blade shape were selected and were tested in a set of 45 simulations, under an array of operating conditions defined by solidity, angle of attack and TSR. Results show that the laminar separation bubble moves towards the leading edge with increasing solidity, angle of attack and TSR. Furthermore, CP plots show an increase in pressure on both surfaces when the airfoil is subject to solidity effects, although these effects show an increase in the lift-to-drag ratio at the conditions evaluated.

O presente trabalho apresenta uma metodologia de simulação numérica de perfis aerodinâmicos bidimensionais com foco na utilização para o projeto e otimização de pás e rotores de pequenas turbinas eólicas de eixo horizontal, bem como o emprego desses métodos em simulações nas quais efeitos de alta solidez do rotor e baixos números de Reynolds são avaliados. Essa metodologia inclui geração de malhas, seleção de métodos numéricos e validação, tendo as escolhas sido guiadas pelas práticas mais bem sucedidas na simulação de perfis aerodinâmicos, e foi aplicada na simulação dos aerofólios NACA 0012, S809 e SD7062. O código comercial ANSYS Fluent foi utilizado em todas as simulações. Na simulação de aerofólios isolados a altos números de Reynolds dos perfis NACA 0012 e S809, o modelo Transition SST (γ-Reθ) apresentou resultados mais próximos a dados experimentais do que aqueles apresentados pelo modelo k-ω SST para CL e CD, além de produzir resultados para CP que mostraram boa precisão quando comparados aos mesmos dados experimentais. Resultados de CL, CD, CF e CP são apresentados para 20 diferentes condições de operação às quais o perfil SD7062 foi submetido, com números de Reynolds variando entre 25.000 e 125.000. As distribuições dos dois últimos coeficientes sobre os dorsos do aerofólio evidenciam com clareza a presença e magnitude da bolha de separação laminar. Os coeficientes de sustentação e arrasto mostram o impacto negativo da presença da bolha nessa faixa de números de Reynolds. Além disso, nos casos simulados, o arrasto aumenta em função da diminuição do Re. Um design de pá produzido com o auxílio do código de otimização SWRDC, baseado em algoritmos genéticos, é apresentado. Três seções ao longo da envergadura dessa pá foram simuladas em uma bateria de 45 simulações, sob diversas condições de operação em função de solidez, ângulo de ataque e razão de velocidade de ponta de pá. Esses resultados mostram que a bolha de separação laminar se move na direção do bordo de ataque com o aumento da solidez, do ângulo de ataque e da TSR. Além disso, distribuições do CP mostram aumento de pressão em ambos os dorsos do perfil quando submetido aos efeitos da solidez, embora esses efeitos tenham sido responsáveis por um aumento na relação CL/CD nos casos estudados. / This thesis presents a methodology of two-dimensional airfoil simulation focusing on its application on the design and optimization of blades and rotors of small horizontal axis wind turbines, and its application in a set of numerical simulations involving high rotor solidity and low-Re effects. This methodology includes grid generation, selection of numerical methods and validation, reflecting the most successful practices in airfoil simulation, and was applied in the simulation of the NACA 0012, S809 and SD7062 airfoils. The ANSYS Fluent commercial code was used in all simulations. Results for the isolated NACA 0012 and S809 airfoils at high Reynolds numbers show that the Transition SST (γ-Reθ) turbulence model produces results closer to experimental data than those yielded by the SST k-ω model for CL and CD, having also produced CP plots that show good agreement to the same experimental data. Plots of CL, CD, CF and CP for the SD7062 airfoil are presented, for simulations at 20 different operating conditions. The CF and CP distributions evidence the negative impact of the laminar separation bubble in the range of Reynolds numbers evaluated. Results show that, for Re between 25,000 and 125,000, drag increases with decreasing Re. A blade design generated using the SWRDC optimization code, based on genetic algorithms, is presented. Three sections of the resulting blade shape were selected and were tested in a set of 45 simulations, under an array of operating conditions defined by solidity, angle of attack and TSR. Results show that the laminar separation bubble moves towards the leading edge with increasing solidity, angle of attack and TSR. Furthermore, CP plots show an increase in pressure on both surfaces when the airfoil is subject to solidity effects, although these effects show an increase in the lift-to-drag ratio at the conditions evaluated.