La thèse porte sur l'étude de la réduction de traînée par injection de bulles. La réduction de traînée présente un intérêt pour les applications navales puisqu'elle est issue d'une modification des structures cohérentes qui contribuent le plus à la résistance à l'avancement. Le but de cette étude est d'analyser les mécanismes à l'origine de cette diminution du frottement pariétal. L'approche utilisée dans le cadre de cette étude est numérique, elle emploie le code JADIM par une approche Euler-Lagrange : la phase continue est simulée par Simulation Numérique Directe et la phase dispersée est simulée en suivant individuellement chaque bulle. La configuration retenue dans le cadre de cette étude est celle de l'écoulement de Taylor-Couette (écoulement compris entre deux cylindres en rotation). La première partie de la thèse vise à adapter l'outil numérique employé, afin de pouvoir prendre en compte le retour de la phase dispersée via des termes de forçage dans les équations bilan de matière et de quantité de mouvement. La deuxième partie de la thèse vise à étudier l'écoulement porteur en configuration monophasique, afin de disposer d'une référence sur l'écoulement non perturbé. La troisième partie de la thèse a pour objectif d'étudier la dispersion passive des bulles dans le système, afin d'analyser les mécanismes de migrations mis en jeu. Enfin la dernière partie de la thèse vise à étudier l'influence des bulles sur l'écoulement porteur en analysant l'effet de certains paramètres, notamment le taux de vide et la flottabilité. / The study deals with drag reduction induced by bubble injection, its application concerns naval transport. The aim of the study is to shed more light on mechanisms that are involved in this wall friction reduction. The study is based on a numerical approach, and use the JADIM code with an Euler-Lagrange approach: the continuous phase is solved by Direct Numerical Simulation, and the disperse phase by a tracking of each bubble. Within the framework of this study we consider the Taylor-Couette flow configuration (flow between two concentric cylinders in rotation). The first part of the study deals with the modification of the numerical tool, in order to take into account the influence of the disperse phase on the continuous one through forcing terms in the mass and momentum balance equations. The aim of the second part is to study de Taylor-Couette flow in its monophasic configuration, for the purpose of providing a reference of the undisturbed flow. The third part deals with the passive dispersion of bubble in Taylor-Couette flow, in order to analyze the migration mechanisms involved. And the aim of the last part is to study the effects of the disperse phase on the continuous one, by analyzing the influence of bubbly phase parameters (like void fraction and buoyancy).

Ce travail de thèse, menée dans le cadre d'une convention CIFRE entre TURBOMECA et le CERFACS, s'inscrit dans un contexte d'amélioration des performances des turbines de type axial équipant les turboréacteurs d'hélicoptère. L'une des principales difficultés rencontrée dans cette démarche concerne la maîtrise de la température que voient les pales de ce composant, notamment la roue haute pression. Les travaux de cette thèse s'articulent autour de deux axes principaux: - Le premier traite l'analyse de la Simulations aux Grandes Echelles (SGE) autour de pales. Une approche numérique SGE sur des maillages non-structurés est comparée aux résultats Reynolds Averaged Navier-Stokes (RANS) sur des maillages structurés, usuels dans ce type de configuration, ainsi qu'à une approche SGE sur maillages structurés. La SGE sur maillage non-structuré démontre sa capacité à prendre en compte les phénomènes qui ont un impact sur les flux de chaleur pariétaux. - Le second axe de recherche a pour objectif de développer un outil numérique de couplage pour assurer le transfert d'information entre un code SGE réactif sur maillage non-structuré, employé dans les chambres de combustion, et un code non-réactif en RANS, utilisé par les industriels pour modéliser l'étage turbine. Cet outil a été validé sur plusieurs cas tests qui montrent le potentiel de cette méthodologie pour le couplage multi-composant. / This PhD dissertation, conducted as part of a CIFRE research project between TURBOMECA and CERFACS, deals with improving performance of axial turbines from helicopter engines. One of the main difficulties with such an objective is the control of the temperature prediction around the blades, especially the temperature of the high pressure rotor. The work of this thesis focusses on two axes: - First concerns the analysis of Large Eddy Simulation (LES) predictions around blades: a numerical LES approach on unstructured meshes is compared to Reynolds Averaged Navier-Stokes (RANS) results on structured meshes as well as to LES on structured meshes. LES on unstructured meshes demonstrates its capacity of taking into account the phenomena which have an impact on wall heat flux around blades. - The second axis deals with the development of a numerical tool for coupling and transferring information between a reactive LES code, used in combustion chambers, and a non-reactive RANS solver, employed by industrial actors for modeling the turbine stage. This tool is validated on a number of test cases which show the potential of this methodology for multi-component predictions.

The thesis deals with methodology for computational approaches for numerical simulations of welding and heat treatment of aluminium alloys. The thesis describes improvement of the current methodology for metallurgical part of the numerical analysis of welding, which is important mainly for prediction of dimensions of the heat affected zone (and deformations). The improvement was carried out based on CHD diagram that describes precipitation and dissolution of phases during continuous heating. The thesis also describes carried material measurements (measurement of chemical composition, dilatometric tests, tensile tests of several conditions of materials at temperatures up to 500 °C and measurement of aging curves), which allowed to significantly refine analysis results for the alloys EN AW-5083 and EN AW-6082. Based on an evaluation of the measurements, several conclusions were made. They can be useful for creation of material databases of other aluminium alloys. The thesis also describes quantification of dependence between tensile strength and yield strength on the Vickers hardness for different conditions of EN AW-6082. There is also methodology for numerical simulation of the heat treatment process of heat treatable Al alloys in the dissertation. The methodology is completely new approach which has never been published so far. Application of this method is based on user changes of the material database in software Sysweld after relatively easy measurement of aging curves. Therefore, the methodology can be considered as promising for application in industrial practice.

Cette thèse a pour objet le développement d'un modèle numérique de simulation des fluides fondé sur la méthode Smoothed Particle Hydrodynamics (SPH). SPH est une méthode de simulation numérique sans maillage présentant un certain nombre d'avantages par rapport aux méthodes Eulériennes. Elle permet notamment de modéliser des écoulements à surface libre ou interfaces fortement déformées. Ce travail s'adresse principalement à quatre problématiques liées aux fondements de la méthode SPH : l'imposition des conditions aux limites, la prédiction précise des champs de pression, l'implémentation d'un modèle thermique et la réduction des temps de calcul. L'objectif est de modéliser des écoulements industriels complexes par la méthode SPH, en complément de ce qui peut se faire avec des méthodes à maillage. Typiquement, les problèmes visés sont des écoulements 3-D à surface libre ou confinés, pouvant interagir avec des structures mobiles et/ou transporter des scalaires, notamment des scalaires actifs (e.g. température). Dans ce but, on propose ici un modèle SPH incompressible (ISPH) basé sur une représentation semi-analytique des conditions aux limites. La technique des conditions aux limites semi-analytiques permet d'imposer des conditions sur la pression de manière précise et physique, contrairement à ce qui se fait avec des conditions aux limites classiques en SPH. Un modèle k-epsilon a été incorporé à ce nouveau modèle ISPH, à partir des travaux de Ferrand et al. (2013). Un modèle de flottabilité a également été ajouté, reposant sur l'approximation de Boussinesq. Les interactions entre flottabilité et turbulence sont prises en compte. Enfin, une formulation pour les frontières ouvertes dans le nouveau modèle est établie. La validation du modèle en 2-D a été réalisée sur un ensemble de cas-tests permettant d'estimer les capacités de prédiction du nouveau modèle en ce qui concerne les écoulements isothermes et non-isothermes, laminaires ou turbulents. Des cas confinés sont présentés, ainsi que des écoulements à surface libre (l'un d'eux incluant un corps solide mobile dans l'écoulement). La formulation pour les frontières ouvertes a été testée sur un canal de Poiseuille plan laminaire et sur deux cas de propagation d'une onde solitaire. Des comparaisons sont présentées avec des méthodes à maillage, ainsi qu'avec un modèle SPH quasi-incompressible (WCSPH) avec le même type de conditions aux limites. Les résultats montrent que le modèle permet de représenter des écoulements dans des domaines à géométrie complexe, tout en améliorant la prédiction des champs de pression par rapport à la méthode WCSPH. L'extension du modèle en trois dimensions a été réalisée dans un code massivement parallèle fonctionnant sur carte graphique (GPU). Deux cas de validation en 3-D sont proposés, ainsi que des résultats sur un cas simple d'application en 3-D / In this work a numerical model for fluid flow simulation was developed, based on the Smoothed Particle Hydrodynamics (SPH) method. SPH is a meshless Lagrangian Computational Fluid Dynamics (CFD) method that offers some advantages compared to mesh-based Eulerian methods. In particular, it is able to model flows presenting highly distorted free-surfaces or interfaces. This work tackles four issues concerning the SPH method : the imposition of boundary conditions, the accuracy of the pressure prediction, the modelling of buoyancy effects and the reduction of computational time. The aim is to model complex industrial flows with the SPH method, as a complement of what can be done with mesh-based methods. Typically, the targetted problems are 3-D free-surface or confined flows that may interact with moving solids and/or transport scalars, in particular active scalars (e.g. the temperature). To achieve this goal, a new incompressible SPH (ISPH) model is proposed, based on semi-analytical boundary conditions. This technique for the representation of boundary conditions in SPH makes it possible to accurately prescribe consistent pressure boundary conditions, contrary to what is done with classical boundary conditions in SPH. A k-epsilon turbulence closure is included in the new ISPH model. A buoyancy model was also added, based on the Boussinesq approximation. The interactions between buoyancy and turbulence are modelled. Finally, a formulation for open boundary conditions is proposed in this framework. The 2-D validation was performed on a set of test-cases that made it possible to assess the prediction capabilities of the new model regarding isothermal and non-isothermal flows, in laminar or turbulent regime. Confined cases are presented, as well as free-surface flows (one of them including a moving body in the flow). The open boundary formulation was tested on a laminar plane Poiseuille flow and on two cases of propagation of a solitary wave. Comparisons with mesh-based methods are provided with, as well as comparisons with a weakly-compressible SPH (WCSPH) model using the same kind of boundary conditions. The results show that the model is able to represent flows in complex boundary geometries, while improving the pressure prediction compared to the WCSPH method. The extension of the model to 3-D was done in a massively parallel code running on a Graphic Processing Unit (GPU). Two validation cases in 3-D are presented, as well as preliminary results on a simple 3-D application case

A soldagem por atrito com pino não consumível (SAPNC), processo de união no estado sólido, tornou-se conhecido devido à alta resistência das juntas produzidas em comparação ao metal de base e aos métodos convencionais de união. No entanto, o próprio processo apresenta seus desafios, relacionados principalmente à combinação do efeito de geometrias de ferramenta com os parâmetros utilizados. O desenvolvimento de métodos de simulação numérica tem criado a possibilidade de otimização destes efeitos, prevendo as interações entre os materiais, parâmetros e geometrias de ferramenta com menor custo e tempo. O presente trabalho teve como objetivo simular o processo de soldagem por atrito utilizando método dos elementos finitos (MEF) no software DEFORM 3D e avaliar a capacidade do modelo em representar fenômenos presentes do processo, tais como esforços da ferramenta, ciclo termomecânico do material e microestrutura. O estudo foi realizado em amostras de uma chapa de liga de magnésio AZ31B. Para inclusão da evolução mecânica e microestrutural do material de estudo no modelo, dados foram obtidos pelo estudo da compressão isotérmica da liga AZ31 simulador termomecânico Gleeble, em condições típicas às encontradas no processo de soldagem por atrito em. Os dados de tensão, deformação e microestrutura obtidos nos ensaios de compressão foram tratados analiticamente afim de se obter os parâmetros para as equações de deformação à quente e evolução microestrutural do material de estudo. Ademais, na próxima etapa, utilizou-se um pino roscado e não roscado em soldagens dissimilares afim de analisar o efeito da geometria da ferramenta no fluxo de material. Para auxiliar a análise foram utilizadas técnicas de microscopia óptica, microscopia eletrônica de varredura (MEV) e difração de raios X. Por fim, um modelo numérico de soldagem por atrito elaborado no software DEFORM-3D é apresentado. Os resultados do modelo foram comparados com os resultados experimentais com auxílio de técnicas de caraterização microestrutural, EBSD, ciclos térmicos capturados por termopares e torque das ferramentas. Os resultados e conclusões obtidos no projeto permitiram a identificação do ciclo térmico, mecânico e microestrutural do material durante a soldam por atrito, além da demostração do efeito da geometria para distintos parâmetros de processo, indicando um método alternativo eficiente na otimização de geometrias de ferramenta e busca de parâmetro ótimos do processo de soldagem por atrito com tempo e custo reduzidos. / Friction stir welding (FSW), a solid-state process, has become known due to the high strength of the produced joints compared to the base metal and the conventional welding methods. However, the friction stir welding has its challenges, related with tools geometry and the process parameters. The development of numerical simulation methods has been able to aid in the process optimization, including the study of different materials, parameters and tool geometries with lower cost and time. The obejective of the present work is propose a friction stir welding numerical model through finite element analysis (FEA) in DEFORM 3D software and evaluated its capacity to represent the process features such as the tool chacteristics, the thermomechanical cycle of the material and its microstructure. The material chosen for the study was a magnesium alloy AZ31B. In order to include the mechanical and microstructural evolution of the study material in the model, data were obtained through isothermal compression of the AZ31 in Gleeble thermomechanical simulator, under typical conditions found in the friction welding process. Stress, strain and microstructure data obtained in the compression tests were analyzed analytically to obtain the parameters for the hot deformation equations and microstructural evolution of the material. Moreover, a threaded and non-threaded pin in dissimilar welds was used to verify the effect of tool geometry in the material flow during the friction stir welding process. The evaluation was made with the support of optical microscopy and scanning electron microscopy (SEM). Then, a numerical model of friction welding developed in the DEFORM-3D software is presented. The results of the model were compared with experimental results supported by microstructural characterization techniques, EBSD, temperature profiles captured by thermocouples and tool torque response. The results and conclusions obtained in the project allowed the identification of the thermal, mechanical and microstructural cycle of the material during the friction stir welding process, besides the demonstration of the effect of the tool geometry for different process parameters, indicating an efficient alternative method in the optimization of tool geometries and optimal parameter for the friction welding process with reduced time and cost.

Dans cette thèse, des simulations numériques ont d'abord été effectuées avec le logiciel FLAC (Itasca) sur un modèle de pente élastique linéaire homogène pour caractériser l'amplification de l'accélération le long de la surface située le long et à l’arrière de la crête d'une pente, et évaluer ainsi l'effet de la topographie sur l'amplification de l'accélération. L'interaction entre la fréquence du signal sismique appliqué à la base du modèle et l'angle et la hauteur de la pente a été particulièrement étudiée. Il a été constaté que le facteur d’amplification de l’accélération varie de manière significative avec l’angle de et la hauteur de la pente, la fréquence et la durée (nombre de cycle) du signal. De plus, l'amplification du mouvement du sol due à la topographie de la pente est influencée de manière significative par l'effet de couplage complexe entre les ondes incidentes et les ondes réfléchies sur la topographie, et qu’elle est fortement contrôlée par le rapport entre la longueur d'onde du signal incident et la hauteur de la pente.Les simulations numériques sont basées sur une étude géotechnique et une modélisation géomécanique nécessitant de valider les résultats par des comparaisons entre les résultats de modélisations et les données provenant des observations sur le terrain. L’analyse des domaines de fréquence, telle que la densité spectrale et la réponse en fréquence, est un moyen performant pour comprendre les caractéristiques des processus et les divers phénomènes qui ne peuvent pas être expliqués dans le domaine temporel. À cette fin, une étude de la crête du parc Xishan à Zigong au Sichuan en Chine a été réalisée. Les amplifications du site associées au mouvement du sol produit par le séisme de Wenchuan en 2008 ont été évaluées à l'aide de la technique du rapport spectral standard (SSR) et de la méthode d'accélération quadratique moyenne (arms) dans le domaine temporel. Une analyse numérique à 2D utilisant la méthode des différences finies au moyen du logiciel FLAC (Itasca) a été ensuite mise en œuvre et les résultats ont été comparés aux mesures de terrain. Les pics “simulés” des amplifications spectrales sont toujours inférieurs à ceux dérivés des enregistrements de terrain. L'effet d'atténuation important sur le mouvement d'entrée pour les hautes fréquences met en évidence le fait qu'un rapport d'amortissement du signal ne représente pas correctement la dissipation d'énergie dans les simulations numériques. Des amplifications significatives se sont produites à des fréquences élevées (> 10 Hz) et sont considérées comme résultant de conditions locales spécifiques telles que la fracturation des roches et les marches de faîtage; ils ne se produisent donc pas nécessairement au sommet de la colline.Enfin, des études paramétriques ont été réalisées avec des modèles élastiques en termes de diverses géométries de pente 2D et de couches géologiques de subsurface pour caractériser les amplifications du mouvement du sol. L’analyse paramétrique a pour but de comprendre le rôle joué par ces couches de surface, l’angle de la pente et la hauteur de la pente sur l’amplification du mouvement du sol,et donc d’évaluer si l’amplification du site peut être responsable du déclenchement du glissement de terrain. Ensuite, l'analyse dynamique sur des modèles de pente pour différentes magnitudes a été effectuée et une rupture de pente basée sur le déplacement a été créée pour évaluer la stabilité de la pente du site de Las Colinas au Salvador. Les résultats numériques ont clairement montré que les effets de site peuvent avoir induit d'importantes amplifications du mouvement du sol qui ont contribué à déclencher des glissements de terrain. / In this research work, numerical simulations using the finite difference FLAC software (Itasca) were first conducted with a homogeneous linear elastic slope model in order to characterize the acceleration amplification along the slope surface and behind the slope crest, and then to evaluate the topographic effect on the acceleration amplification. The interaction between the frequency of the seismic input motion applied at the base of the model with the slope angle and height has been deeply investigated. It was found that significant changes in the acceleration amplification factor result from variations in the slope angle and height as well as the signal frequency and duration. In addition, it has been shown that the ground motion amplification due to slope topography result from complex coupling effects between the input waves and the reflected waves on the topographic features and is highly controlled by the ratio between the wavelength of the input signal and the slope height.Numerical simulations are based on geotechnical investigations and geotechnical modeling, and it is necessary to validate the results through comparisons between modeling results and field observations. Frequency domain analysis such as spectral density and frequency response are an effective way to understand process characteristics and the various phenomena that cannot be explained in the time domain. For this purpose, a case study at Xishan Park ridge in Zigong in China has been studied. Site amplifications associated with the ground motion produced by the 2008 Wenchuan earthquake have been evaluated using the Standard Spectral Ratio (SSR) technique and root-mean-square acceleration (arms) method in time domain. 2D numerical analysis using finite difference method using the FLAC software (Itasca) has been then performed and results have been compared with monitoring data. The “simulated” peaks of the spectral amplifications are always lower than those derived from the field records. The strong attenuation of input motion at high frequencies highlights the shortcoming that a signal damping ratio does not adequately represent the energy dissipation in numerical simulations. Significant amplifications occurred at high frequencies (>10 Hz) and are considered to result from local specific conditions such as rock fracturing and ridge steps; thus they do not necessarily occur at the top of the hill. Finally, parametric studies were performed with elastic models in terms of various 2D slope geometries and geological layers to characterize the ground motion amplifications. The purpose of the parametric analysis is to understand the role of the geological layer, slope angle and slope height on the ground motion amplification, and thus to estimate if site amplifications could be responsible for the triggering of landslide. Then, the dynamic analysis on the slope model for different seismic magnitudes was performed and a slope failure based on displacement was created to evaluate the Las Colinas slope stability in Salvador. The numerical results clearly showed that site effects can have induced significant ground motion amplifications that contributed to trigger landslides.

L'étude de l'écoulement à l'aval d'une ride a un intérêt primordial dans la dynamique et l'évolution des rivières, des milieux côtiers ou des estuaires. Une des questions au coeur de ces écoulements est liée aux mécanismes d'interaction entre les particules et l'écoulement. Cette interaction donne souvent lieu à la formation de structures ondulées (rides ou dunes). Ce couplage est engendré au niveau de l'écoulement moyen, de la forme de la dune mais aussi au niveau de la macro turbulence et des structures tourbillonnaires instationnaires générées par la présence même des formes sédimentaires. L'identification des différents mécanismes et processus hydrodynamiques générés par la présence de dunes ou rides est exposée en détail par l'examen de l'écoulement laminaire à l'aval d'une ride fixe et isolée. Des techniques de mesure optiques 2D (PIV, visualisations) et 3D (Stéréo-PIV, tomographie laser) couplées à une étude numérique avec un code industriel, permettent de mettre en évidence l'instationarité, la tridimensionnalité de l'écoulement ainsi que la dynamique tourbillonnaire de la zone de recirculation à l'aval de la ride. L'impact de l'écoulement turbulent sur la naissance de dunes isolées est analysé au moyen d'une étude détaillée sur le transport de particules à partir d'essais menés en canal hydro-sédimentaire. Le rôle particulier de la zone de recirculation à l'aval de la dune est mis en évidence à l'aide d'un suivi spatio-temporel du transport des particules entre sa crête et sa face d'avalanche. Finalement, l'analyse et l'influence des conditions hydrauliques sur le seuil critique de mise en mouvement d'un lit de particules ainsi que la formation et la migration d / The aim of this study is to examine the processes leading to development a bed river, estuary or coastal environments morphology. The ability to investigate the complex nature of the interaction between fluids and sediments mechanisms and its role in bed transport and river stability is important to understand river evolution. Dunes or ripples are in frequent interaction with the bed. Hence, the topology of dune is related to the macroturbulence of the flow, mean flow field and the instantaneous structures of the vortices generated by these forms. Details of different mechanisms and hydrodynamic process generated behind a fixed single ripple are exposed by examining a laminar flow over the dune itself. Measurements with two-component Particle Image Velocimetry, three-component Stereo-PIV and flow visualization coupled with a numerical studies are performed to acquire and to obtain a detailed knowledge of the flow over the dune concerning the three-dimensionality, the instantaneous behavior of the flow and the large dynamic of vortex in the recirculation zone along the ripple. A set experiment generating turbulent flow is conducted in a hydro-sedimentary channel to detail the quantitative measurement of bedload transport processes in order to determine the effects of the turbulent flow on dune creation. A spatio-temporal monitoring of particles transport from crest to dune slip face is conducted to point the particular role of the recirculation region. Finally, the analyze and the effect of hydraulics conditions on the critical shear stresses for incipient particle motion as well as the formation and the migration of the mobile dune are emphasized by a geomorphological st

<div>Bladeless fans are well known for their unique shape and efficient performance, which have a great impact on the fan industry. At present, there are few studies on the bladeless fan and the research on the improvement of fan design is a lack. Therefore, the study on the performance of the bladeless fan with different design is the main purpose of this thesis. </div><div>In the present study, a bladeless fan prototype is created and studied by numerical simulations. When characterizing the aerodynamic and aeroacoustic performances of the bladeless fan, the entire fan prototype, including wind channel, base, rotor and stator, is adopted; when investigating the influence of the wind channel's geometric parameters, only wind channel is considered in simulations. The influence of the slit width, the height of the cross-section, the slit location and the profile of the cross-section are studied. </div><div><br></div><div>It is found that the flow outside the bladeless fan consists of the air blown out from the wind channel and entrained from the back and side of the fan. The air entrained from the side is the main source of flow rate increase. As for the aeroacoustic performance, the rotor and stator inside the base are the predominated source of the noise generated by the bladeless fan. </div><div>The performances of the bladeless fan are very sensitive to the geometric details of the wind channel. The generated noise always increases as the wind strength improves. The slit width of the wind channel has the greatest impact. With the slit moves away from the leading edge, the wind produced by the bladeless fan becomes more powerful and the noise becomes louder. The cross-sectional height of 4cm has the best aerodynamic performance but the generated noise is a little larger than other designs. The profile of the cross-section shows insignificant influence on the performances. </div>

O método de Lattice-Boltzmann (MLB) vem ganhando destaque nas últimas décadas pela sua capacidade de solução de escoamentos complexos como escoamentos multifásicos e multicomponentes, meios porosos e magnetohidrodinâmicos. Também existem extensões do método para a solução de problemas de advecção-difusão, que permitem acoplamento dessa metodologia para a solução numérica do conjunto de equação Navier-Stokes-Fourier. No trabalho presente, os objetivos iniciais podem ser resumidos no estudo dos conceitos básicos necessários para entender a derivação do método a partir da teoria cinética e estudo do método de Lattice Boltzmann, com operador de colisão mais simples conhecido como operador BGK, para problemas bidimensionais térmicos e fluidodinâmicos. A implementação numérica do método foi realizada em linguagem C, Matlab e CUDA C, com foco na solução de cinco problemas incompressíveis e laminares em regime permanente, conhecidos na literatura: equação viscosa de Burgers, escoamento de Poiseuille com transferência de calor, convecção natural em uma cavidade quadrada, regimes de convecção natural, forçada e mista em uma cavidade com uma das fronteiras móvel, e por fim, convecção forçada em uma cavidade ventilada, com uma entrada e uma saída. Além disso, um pequeno estudo no tempo computacional utilizando três implementações distintas foram testadas: implementação em série, uso de interpolações entre malhas grosseiras como condição inicial para malhas mais refinadas, e por fim, a adição da implementação do código em paralelo. Os ganhos de tempo entre a primeira e segunda estratégia ficaram entre 1.5 e 6, ao passo que o código paralelizado mostrou-se entre 20 e 25 vezes mais rápido que a segunda estratégia testada, comprovando o benefício de utilizar o processamento em paralelo em unidades gráficas. Os resultados obtidos para os problemas foram comparados com outros trabalhos da literatura, mostrando boa concordância para os primeiros quatro problemas estudados. Para a cavidade ventilada, diferenças relativas de até 15.7% no coeficiente de troca de calor e de até 28.38% para o coeficiente de queda de pressão adimensional foram observadas. Análises a respeito dos termos de erros do método apresentado, e a utilização de outras metodologias com método de Lattice Boltzmann, como por exemplo, o emprego de outros operadores de colisão, para trazerem mais estabilidade e precisão, podem elucidar melhor as divergências observados entre o trabalho presente e outros trabalhos da literatura. / Lattice-Boltzmann Method (LBM) has gained attention over last decades due to its performance in solving complex flows such as multiphase and multicomponent flow, porous media and magnetohydrodynamics. There are also further techniques which makes LBM able to solve advection-difussion problems, which allows coupling this methodology to solve Navier-Stokes-Fourier equations. In this work, initial goals are, in a few words, studying main concepts required to understand numerical method origins from kinectic thery, and studying the method implemetantion to solve 2D fluid dynamic and thermal problems. Numerical implemetation was written in C, CUDA C and Matlab languages, keeping in focus five different cases of laminar incompressible flows in steady state: viscous Burgers\' equation, thermal Poiseuille, natural convection in square cavities, natural, forced and mixed convection in a lid driven cavity, and, finally, forced convection in a ventilated cavity, with one inlet and outlet ports. Besides that, a quick study regarding impact in simulation time of three distinct approaches was conducted. First approach consists in implementing a serial code, the second in using interpolation for coarser grids results as initial condition for finer meshes, and the last one is adding parallelized code implementation. Time gains between first and second approach range from 1.5 to 6, while parallelized code was able to converge from 20 to 25 times faster than second approach, confirming great benefits in using graphics processing units. Results obtained from numerical solutions of problems were compared with other works from literature, and a good agreement among them was observed, specially in the first four problems studied. In ventilated cavity problem, relative differences up to 15.7% in heat transfer coefficient and up to 28.38% in dimensionless pressure drop coefficient were observed. A further error terms analysis of method used in this work, and use of distinct approaches, such as different collision operators, in order to increase numerical solution stability and accurarcy, may shed a light on results divergences observed between this work and others from literature.

Avec les dernières augmentations de l'intensité maximale de laser réalisable grâce à de courtes impulsions à haute puissance (gamme femtoseconde) un intérêt a surgi dans les sources de plasma laser potentiels. Les lasers sont utilisés en radiographie proton, allumage rapide, hadronthérapie, la production de radioisotopes et de laboratoire astrophysique. Au cours de l'interaction laser-cible, les ions sont accélérés par des processus physiques différents, en fonction de la zone de la cible. Tous ces mécanismes ont un point commun: les ions sont accélérés par des champs électriques intenses, qui se produisent en raison de la séparation de forte charge induite par l'interaction de l'impulsion laser avec la cible, directement ou indirectement. Deux principales sources distinctes pour le déplacement de charge peuvent être mis en évidence. Le premier est le gradient de charge provoquée par l'action directe de la force ponderomotive de laser sur les électrons dans la surface avant de la cible, qui est la prémisse pour le processus d'accélération des radiations de pression (RPA). Une deuxième source peut être identifiée comme provenant du rayonnement laser qui est transformée en énergie cinétique d'une population d'électrons relativistes chaud (~ quelques MeV). Les électrons chauds se déplacent et font recirculer à travers la cible et forment un nuage d'électrons relativistes à la sortie de la cible dans le vide. Ce nuage, qui se prolonge pour plusieurs longueurs de Debye, crée un champ électrique extrêmement intense longitudinal, la plupart du temps dirigé le long de la surface normale, ce qui, par conséquent, est la cause de l'accélération d'ions efficace, qui conduit à l'accélération cible normale gaine (TNSA) processus . Le mécanisme TNSA permet d'utiliser des géométries différentes cibles afin de parvenir à une meilleure focalisation des faisceaux de particules de l'ordre de plusieurs dizaines de microns, avec des densités d'énergie élevées. Les électrons chauds sont produits par l'irradiation d'une feuille solide avec une impulsion laser intense; ces électrons sont transportés à travers la cible, la formation d'un champ électrostatique fort, normal à la surface cible. Protons et les ions chargés positivement de la surface arrière de la cible sont accélérés par ce domaine jusqu'à ce que la charge de l'électron est compensée. La densité d'électrons chauds et la température dans le vide arrière dépendent des propriétés géométriques et de composition cibles tels que la courbure de la cible, les structures de mise au point d'impulsion et de microstructure pour l'accélération de protons améliorée. Au cours de ma première année, j'ai étudié les effets de la géométrie de la cible sur le proton et l'ion énergie et la distribution angulaire afin d'optimiser les faisceaux de particules laser accéléré au moyen de deux dimensions (2D) particule-in-cell (PIC) simulations de l'interaction de l'ultra-court impulsions laser avec plusieurs cibles microstructurées. Également au cours de cette année, je l'ai étudié la théorie derrière les modèles utilisés. / With the latest increases in maximum laser intensity achievable through short pulses at high power (femtosecond range) an interest has arisen in potential laser plasma sources. Lasers are used in proton radiography, rapid ignition, hadrontherapy, production of radioisotopes and astrophysical laboratory. During the laser-target interaction, the ions are accelerated by different physical processes, depending on the area of ​​the target. All these mechanisms have one thing in common: the ions are accelerated by intense electric fields, which occur due to the separation of high charge induced by the interaction of the laser pulse with the target, directly or indirectly. Two main distinct sources for charge displacement can be identified. The first is the charge gradient caused by the direct action of the laser ponderomotive force on the electrons in the front surface of the target, which is the premise for the pressure ramping acceleration (RPA) process. A second source can be identified as coming from the laser radiation which is transformed into kinetic energy of a hot relativistic electron population (~ a few MeV). The hot electrons move and recirculate through the target and form a cloud of relativistic electrons at the exit of the target in a vacuum. This cloud, which extends for several lengths of Debye, creates an extremely intense longitudinal electric field, mostly directed along the normal surface, which is therefore the cause of effective ion acceleration, which leads to the normal target sheath acceleration (TNSA) process. The TNSA mechanism makes it possible to use different target geometries in order to obtain a better focusing of the beams of particles on the order of several tens of microns, with high energy densities. Hot electrons are produced by irradiating a solid sheet with an intense laser pulse; these electrons are transported through the target, forming a strong electrostatic field, normal to the target surface. Protons and positively charged ions from the back surface of the target are accelerated by this domain until the charge of the electron is compensated. The density of hot electrons and the temperature in the back vacuum depend on the target geometric and compositional properties such as target curvature, pulse and microstructure tuning structures for enhanced proton acceleration. In my first year I studied the effects of target geometry on the proton and energy ion and angular distribution in order to optimize the accelerated laser particle beams by means of two-dimensional (2D) particle -in-cell (PIC) simulations of the interaction of ultra-short laser pulses with several microstructured targets. Also during this year, I studied the theory behind the models used.