L'objectif de c e mémoire est d'apporter une contribution à la modélisation et la simulation numérique de la convection thermosolutale de mélanges binaires de gaz parfaits contenus dans des cavités. Un modèle a été élaboré en se basant sur l'approximation de faible compressibilité. Le premier chapitre précise la démarche suivie dans la modélisation et une formulation originale en est déduite afin de traiter les différents types de conditions aux limites et de conditions de références hydrostatiques analysés dans le mémoire. Les variations de masse volumique sont déduites de la loi des gaz parfaits et la pression thermodynamique est calculée à partir de la conservation de la masse totale. La méthode numérique repose sur la méthode des volumes finis mise en uvre sur des maillages décalés. Le couplage vitesse-pression est traité par un nouvel algorithme dont l'efficacité est discutée en détail. La démarche numérique est validée via des comparaisons avec des solutions de références, en régime stationnaire comme en régime transitoire pour des écoulements transitionnels. Dans la seconde partie du mémoire, on considère d'abord la convection thermosolutale dans une cavité rectangulaire verticale dans le cas où les écoulements sont induits par des gradients horizontaux de température et de concentration. On discute en particulier les limites de l'approximation d'extrême dilution. La condensation de vapeur d'eau et l'évaporation d'un film d'eau liquide sur les parois d'une cavité sont ensuite étudiées en régime transitoire. Ces changements de phase surfaciques sont associés à la convection naturelle dans une cavité dont les températures des quatre parois varient au cours du temps

Computational fluid dynamics (CFD) is a significant tool routinely used indesign and optimization in aerospace industry. Often cases with unsteadyflows must be computed, and the long compute times of standard methods hasmotivated the present work on new implicit methods to replace the standardexplicit schemes. The implementation and numerical experiments were donewith the Swedish national flow solver Edge, developed by FOI,universities, and collaboration partners.The work is concentrated on a Lower-Upper Symmetric Gauss-Seidel (LU-SGS)type of time stepping. For the very anisotropic grids needed forReynolds-Averaged Navier-Stokes (RANS) computations of turbulent boundary layers,LU-SGS is combined with a line-implicit technique.  The inviscid flux Jacobians which contribute to the diagonalblocks of the system matrix are based on a flux splitting method with upwind type dissipation giving  control over diagonal dominance and artificial dissipation.The method is  controlled by several parameters, and comprehensivenumerical experiments were carried out to identify their influence andinteraction so that close to optimal values can be suggested. As an example,the optimal number of iterations carried out in a time-step increases with increased resolution of the computational grid.The numbering of the unknowns is important, and the numberings produced by mesh generators of Delaunay- and advancing front-type wereamong the best.The solver has been parallelized with the Message Passing Interface (MPI) for runs on multi-processor hardware,and its performance scales with the number of processors at least asefficiently as the explicit methods. The new method saves typicallybetween 50 and 80 percent of the runtime, depending on the case, andthe largest computations have reached 110M grid nodes. Theclassical multigrid acceleration for 3D RANS simulations was foundineffective in the cases tested in combination with the LU-SGS solverusing optimal parameters. Finally, preliminary time-accurate simulations for unsteady flows have shown promising results. / <p>QC 20141201</p>

Acoustic noise pollution is an environmental aggressor in everyday life. Aero- dynamically generated noise annoys and was linked with health issues. It may be caused by high-speed turbulent free flows (e.g. aircraft jet exhausts), by airflow interacting with solid surfaces (e.g. fan noise, wind turbine noise), or it may arise within a confined flow environment (e.g. air ventilation systems, refrigeration systems). Hence, reducing the acoustic noise levels would result in a better life quality, where a systematic approach to decrease the acoustic noise radiation is required to guarantee optimal results. Computational predic- tion methods able to provide all the required flow quantities with the desired temporal and spatial resolutions are perfectly suited in such application areas, when supplementing restricted experimental investigations. This thesis focuses on the use of numerical methodologies in compressible flow applications to understand aerodynamically noise generation mechanisms and to assess technologies used to suppress it. Robust and fast steady-state Reynolds Averaged Navier-Stokes (RANS) based formulations are employed for the optimal design process, while the high fidelity Large Eddy Simulation (LES) approach is utilized to reveal the detailed flow physics and to investigate the acoustic noise production mechanisms. The employment of fast methods on a wide range of cases represents a brute-force strategy used to scrutinize the optimization parameter space and to provide general behavioral trends. This in combination with accurate simulations performed for particular condi- tions of interest becomes a very powerful approach. Advance post-processing techniques (i.e. Proper Orthogonal Decomposition and Dynamic Mode Decomposition) have been employed to analyze the intricate, highly turbulent flows. The impact of using fluidic injection inside a convergent-divergent nozzle for acoustic noise suppression is analyzed, first using steady-state RANS simulations. More than 250 cases are investigated for the optimal injection location and angle, amount of injected flow and operating conditions. Based on a-priori established criteria, a few optimal candidate solutions are detected from which one geometrical configuration is selected for being thoroughly investigated by using detailed LES calculations. This allows analyzing the unsteady shock pattern movement and the flow structures resulting with fluidic injec- tion. When investigating external fluidic injection configurations, some lead to a high amplitude shock associated noise, so-called screech tones. Such unsteady phenomena can be captured and explained only by using unsteady simulations. Another complex flow scenario demonstrated using LES is that of a high ve- locity jet ejected into a confined convergent-divergent ejector (i.e. a jet pump). The standing wave pattern developed in the confined channel and captured by LES, significantly alters the acoustic noise production. Steady-state methods failed to predict such events. The unsteady highly resolved simulations proved to be essential for analyzing flow and acoustics phenomena in complex problems. This becomes a very powerful approach when is used together with steady-state, low time-consuming formulations and when complemented with experimental measurements. / <p>QC 20141202</p>

Design of landfills must consider both stability and integrity of the lining system. Therefore, stresses and strains in both mineral and geosynthetic lining materials must be controlled. Interaction between waste and barrier system is of particular importance for assessing the stability and structural integrity of steep non-self supporting barrier systems. The most appropriate approach to assess the interaction is the use of numerical modelling techniques, and therefore an appropriate constitutive model for waste material is required to represent its mechanical behaviour. In a literature review the key aspects of mechanical behaviour of municipal solid waste (MSW) were investigated, including the influence of compressible and reinforcing particles on compression and shear behaviour of MSW were identified. Constitutive modelling of both MSW and soil material were reviewed, based on which the methodology for this study have been developed. In addition, requirements of an appropriate constitutive model for MSW have been suggested from the numerical modelling experience, and a framework to develop a constitutive model for MSW was produced. A one-dimensional compression model was developed by including the influence of compressible particles on MSW compression behaviour. One-dimensional compression tests on both real and synthetic waste samples were modelled and the results have shown that the compression model can reproduce the measured behaviour. A fibre reinforcing model was developed by including the influence of reinforcing particles on MSW shear behaviour. A triaxial compression test on fibre reinforced sand was modelled and the results have shown that the reinforcing model can predict its shear strength. A constitutive model for MSW has been developed by combining the Modified Cam-Clay with the one-dimensional compression and the fibre reinforcing models. Typical MSW triaxial compression tests have been modelled and the results have shown that the MSW model can reproduce the stress-strain behaviour in specific strain ranges. The constitutive model for MSW has been coded into a non-linear elasto-plastic finite element method program. Comparisons between the finite element analysis results and the analytical solutions have been performed and good agreements have been obtained.

This work develops finite element methods with high order stabilization, and robust and efficient adaptive algorithms for Large Eddy Simulation of turbulent compressible flows. The equations are approximated by continuous piecewise linear functions in space, and the time discretization is done in implicit/explicit fashion: the second order Crank-Nicholson method and third/fourth order explicit Runge-Kutta methods. The full residual of the system and the entropy residual, are used in the construction of the stabilization terms. These methods are consistent for the exact solution, conserves all the quantities, such as mass, momentum and energy, is accurate and very simple to implement. We prove convergence of the method for scalar conservation laws in the case of an implicit scheme. The convergence analysis is based on showing that the approximation is uniformly bounded, weakly consistent with all entropy inequalities, and strongly consistent with the initial data. The convergence of the explicit schemes is tested in numerical examples in 1D, 2D and 3D. To resolve the small scales of the flow, such as turbulence fluctuations, shocks, discontinuities and acoustic waves, the simulation needs very fine meshes. In this thesis, a robust adjoint based adaptive algorithm is developed for the time-dependent compressible Euler/Navier-Stokes equations. The adaptation is driven by the minimization of the error in quantities of interest such as stresses, drag and lift forces, or the mean value of some quantity. The implementation and analysis are validated in computational tests, both with respect to the stabilization and the duality based adaptation. / QC 20110627

O comportamento do escoamento supersônico no interior de bocais convergente-divergente retangulares é investigado numericamente, comparando-se quatro bocais com diferentes seções divergentes, com a mesma razão de aspecto AR=1.14 e mesma relação áreas da saída e da garganta dos bocais NAR=1.43. Os bocais são submetidos a diferentes pressões de admissão do fluido de trabalho, mantendo-se a relação entre a pressão de admissão e de descarga constante NPR=5. As simulações consideram o escoamento em regime permanente, compressível, viscoso, com abordagem baseada na massa específica (abordagem acoplada) , juntamente com o modelo de turbulência − /SST. A qualidade dos resultados é medida empregando-se três níveis de refino da discretização do domínio computacional, observandose a ordem de convergência e o índice de convergência de malhas GCI. Os resultados numéricos mostram que o número de Mach e a temperatura do fluido de trabalho independem da pressão de admissão, ao contrário do comportamento da pressão local e da massa específica. As propriedades do escoamento são fortemente dependentes da variação da geometria, e a variação do ângulo da seção divergente provoca uma mudança direta do número de Mach e inversa da pressão, da temperatura e da massa específica do escoamento no interior dessa seção. As simulações são comparadas com os resultados da teoria isentrópica e mostram que a linha sônica é deslocada do centro geométrico da garganta dos bocais para cada geometria simulada. A comparação com a teoria e com dados experimentais mostra desvios inferiores a 6x10-3 %. O uso do modelo de turbulência − / SST é capaz de resolver o escoamento com boa precisão, prevendo bem seu perfil de velocidades, as ondas de expansão de Prandtl-Meyer, juntamente com as interações dessas ondas com a camada limite. / The behavior of the supersonic flow inside rectangular convergent-divergent nozzle is investigated numerically by comparing four nozzles with different divergent sections, with a common aspect ratio AR=1.14, and the same nozzle exit-to-throat area ratios NAR=1.43. Nozzles are subject to several working fluid inlet pressures, maintaining a constant pressure ratio NPR=5. Simulations assume the flow in steady state, compressible, viscous, using a coupled approach with the turbulence model − /SST. The quality of results is measured by employing three refining levels of the computational domain discretization, observing the order of convergence and the grid convergence index GCI. Numerical results show that the Mach number and the temperature of the working fluid are independent of the inlet pressure, unlike the behavior of local pressure and the density. Flow properties are strongly dependent on the geometry variation, and the change on the angle of divergent section causes a direct effect on the Mach number and inverse on the pressure, the temperature and the density of the flow in this section. Simulations are compared to the results of the isentropic theory and show that the sonic line is offset from the geometric center of the throat nozzle, for each simulated geometry. Results from this work are compared to experimental and theoretical data and show deviations below 6x10-3 %. The − / SST turbulence model is able to solve the flow with good accuracy, and predicts its velocity profile, Prandtl-Meyer expansion waves, and their interactions with the boundary layer.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-07-25T16:40:40Z No. of bitstreams: 1 DÉSIO RAMIREZ DA ROCHA SILVA - DISSERTAÇÃO PPGMAT 2010..pdf: 641903 bytes, checksum: 9b0b6f008468c08a7a9d581e14ef0d13 (MD5) / Made available in DSpace on 2018-07-25T16:40:41Z (GMT). No. of bitstreams: 1 DÉSIO RAMIREZ DA ROCHA SILVA - DISSERTAÇÃO PPGMAT 2010..pdf: 641903 bytes, checksum: 9b0b6f008468c08a7a9d581e14ef0d13 (MD5) Previous issue date: 2010-09 / CNPq / Capes / Neste trabalho, baseado numa seqüência de artigos de David Ho , é provado um teorema sobre a existência de uma solução fraca para um problema de valor inicial envolvendo as equações de Navier-Stokes para o caso de um escoamento unidimensional de um fluido compressível. São consideradas como hipóteses básicas a ausência de forças externas e que a pressão seja uma função contínua positiva crescente da densidade, cuja derivada também seja contínua. Quanto aos dados iniciais, estes podem possuir descontinuidades do tipo salto, não necessariamente pequenos, podendo se comportar inclusive como funções constantes por partes, em particular dados de Riemann. Tal teorema é provado baseado numa seqüência de lemas e proposições que fornecem estimativas para soluções aproximadas suaves obtidas a partir de dados regularizados. A solução nal é obtida por um processo de passagem ao limite das soluções aproximadas / In this work, based on a serie of papers by David Ho , it is proved a theorem on the existence of a weak solution to the initial value problem for the Navier-Stokes equations for a one space dimension ow of a compressible uid. It is assumed the absence of external forces and that the pressure is a continuous positive increasing function of density with the derivative also continuous. Concerning the initial data, they are allowed to have large jump discontinuities, such as piecewise constant functions, in particular Riemann data. The proof of the theorem is based on a sequence of lemmas and propositions which give estimates on the approximate smooth solutions obtained under regularized data. The nal solution is obtained by a limit process on the approximate solutions.

O comportamento do escoamento supersônico no interior de bocais convergente-divergente retangulares é investigado numericamente, comparando-se quatro bocais com diferentes seções divergentes, com a mesma razão de aspecto AR=1.14 e mesma relação áreas da saída e da garganta dos bocais NAR=1.43. Os bocais são submetidos a diferentes pressões de admissão do fluido de trabalho, mantendo-se a relação entre a pressão de admissão e de descarga constante NPR=5. As simulações consideram o escoamento em regime permanente, compressível, viscoso, com abordagem baseada na massa específica (abordagem acoplada) , juntamente com o modelo de turbulência − /SST. A qualidade dos resultados é medida empregando-se três níveis de refino da discretização do domínio computacional, observandose a ordem de convergência e o índice de convergência de malhas GCI. Os resultados numéricos mostram que o número de Mach e a temperatura do fluido de trabalho independem da pressão de admissão, ao contrário do comportamento da pressão local e da massa específica. As propriedades do escoamento são fortemente dependentes da variação da geometria, e a variação do ângulo da seção divergente provoca uma mudança direta do número de Mach e inversa da pressão, da temperatura e da massa específica do escoamento no interior dessa seção. As simulações são comparadas com os resultados da teoria isentrópica e mostram que a linha sônica é deslocada do centro geométrico da garganta dos bocais para cada geometria simulada. A comparação com a teoria e com dados experimentais mostra desvios inferiores a 6x10-3 %. O uso do modelo de turbulência − / SST é capaz de resolver o escoamento com boa precisão, prevendo bem seu perfil de velocidades, as ondas de expansão de Prandtl-Meyer, juntamente com as interações dessas ondas com a camada limite. / The behavior of the supersonic flow inside rectangular convergent-divergent nozzle is investigated numerically by comparing four nozzles with different divergent sections, with a common aspect ratio AR=1.14, and the same nozzle exit-to-throat area ratios NAR=1.43. Nozzles are subject to several working fluid inlet pressures, maintaining a constant pressure ratio NPR=5. Simulations assume the flow in steady state, compressible, viscous, using a coupled approach with the turbulence model − /SST. The quality of results is measured by employing three refining levels of the computational domain discretization, observing the order of convergence and the grid convergence index GCI. Numerical results show that the Mach number and the temperature of the working fluid are independent of the inlet pressure, unlike the behavior of local pressure and the density. Flow properties are strongly dependent on the geometry variation, and the change on the angle of divergent section causes a direct effect on the Mach number and inverse on the pressure, the temperature and the density of the flow in this section. Simulations are compared to the results of the isentropic theory and show that the sonic line is offset from the geometric center of the throat nozzle, for each simulated geometry. Results from this work are compared to experimental and theoretical data and show deviations below 6x10-3 %. The − / SST turbulence model is able to solve the flow with good accuracy, and predicts its velocity profile, Prandtl-Meyer expansion waves, and their interactions with the boundary layer.

La simulation de systèmes d'ingénierie non linéaire complexes tels que les écoulements de fluide compressibles peut être ciblée pour rendre plus efficace et précise l'approximation d'une quantité spécifique (scalaire) d'intérêt du système. En mettant de côté l'erreur de modélisation et l'incertitude paramétrique, on peut y parvenir en combinant des estimations d'erreurs axées sur des objectifs et des raffinements adaptatifs de maillage spatial anisotrope. A cette fin, un cadre élégant et efficace est celui de l'adaptation dite basé-métrique où une estimation d'erreur a priori est utilisée comme indicateur d’adaptation de maillage. Dans cette thèse on propose une nouvelle extension de cette approche au cas des approximations de système portant une composante stochastique. Dans ce cas, un problème d'optimisation est formulé et résolu pour un meilleur contrôle des sources d'erreurs. Ce problème est posé dans le cadre continu de l'espace de métrique riemannien. Des développements algorithmiques sont également proposés afin de déterminer les sources dominates d’erreur et effectuer l’adaptation dans les espaces physique ou des paramètres incertains. L’approche proposé est testée sur divers problèmes comprenant une entrée de scramjet supersonique soumise à des incertitudes paramétriques géométriques et opérationnelles. Il est démontré que cette approche est capable de bien capturé les singularités dans l’escape stochastique, tout en équilibrant le budget de calcul et les raffinements de maillage dans les deux espaces. / The simulation of complex nonlinear engineering systems such as compressible fluid flows may be targeted to make more efficient and accurate the approximation of a specific (scalar) quantity of interest of the system. Putting aside modeling error and parametric uncertainty, this may be achieved by combining goal-oriented error estimates and adaptive anisotropic spatial mesh refinements. To this end, an elegant and efficient framework is the one of (Riemannian) metric-based adaptation where a goal-based a priori error estimation is used as indicator for adaptivity. This thesis proposes a novel extension of this approach to the case of aforementioned system approximations bearing a stochastic component. In this case, an optimisation problem leading to the best control of the distinct sources of errors is formulated in the continuous framework of the Riemannian metric space. Algorithmic developments are also presented in order to quantify and adaptively adjust the error components in the deterministic and stochastic approximation spaces. The capability of the proposed method is tested on various problems including a supersonic scramjet inlet subject to geometrical and operational parametric uncertainties. It is demonstrated to accurately capture discontinuous features of stochastic compressible flows impacting pressure-related quantities of interest, while balancing computational budget and refinements in both spaces.

O presente trabalho tem por objetivo o estudo da otimização multiobjetivo aplicada ao projeto de perfis aerodinâmicos em regime transônico, analisando comparativamente diferentes formas de definir as funções objetivo. A otimização é efetuada pelo algoritmo genético NSGA-II. Os resultados são avaliados utilizando métricas de diversidade da população e otimalidade das soluções, das quais duas são propostas. As funções objetivo são constituidas de diferentes parametrizações da geometria e diferentes técnicas de simulação numérica. A parametrização da geometria é feita utilizando a paramentrização Parsec ou a parametrização baseada em pontos de controle. A discretização do domínio espacial é feita utilizando malha estruturada conformada ao perfil e suavização por EDP elíptica. As duas técnicas de volumes finitos com diferentes modelos para o cálculo do fluxo na face do volume implementadas foram o método de Jameson (esquema centrado) e o método de Roe (esquema upwind). As comparações feitas são as seguintes: utilização de modelo viscoso e invíscido, com o uso do código Mses com a parametrização por ponto de controle; a utilização da parametrização por ponto de controle e parametrização Parsec usando o método de Jameson; e a comparação entre o método centrado e o upwind, utilizando a parametrização Parsec. Conclui-se dos resultados obtidos que a utilização da parametrização por pontos de controle é melhor. Entretanto, ainda é necessária a utilização de uma parametrização que garanta maior suavidade ou a imposição de restrições sobre a suavidade da solução. A utilização do modelo viscoso torna os resultados da otimização melhores do ponto de vista da otimalidade. Na utilização de modelos de correção viscosa, como no caso do Mses, é necessária a utilização de métodos invíscidos que forneçam resultados com maior representatividade física / The objective of present study is analyze the multi-objective optimization applied to transonic airfoils project comparing different ways to define the objective functions. The optimization is evaluated by the genetic algorithm NSGA-II. The results is analyzed using metrics of diversity and optimality for multi-objective problems, which two are proposed. The objective functions are defined by different parametrizations of geometry and different techniques of numerical simulation. The geometry parametrization was made by two distinct forms: using Parsec parametrization; and the control points based parametrization. The space domain discretization was made using structured body-fitted mesh with elliptical PDE smooth. A finite volume code with two different techniques for calculations of flux interface had been implemented: the Jamesons method (centered); and the Roes method ( it upwind). For viscous model usage analysis was used the Mses code that has implemented a finite volumes technique with viscous model correction. The following comparisons has been made: viscous and inviscid model using the Mses code with the control points parametrization; the control points and Parsec parametrizations using the Jamesons method; and the comparison among the centered method and upwind using the parametrization Parsec. From the results, it is concluded that the used of control points parametrization is interesting. Although, is still needed the used of a parametrization that guarantees a better smoothness or the imposes of a geometrical or property distribution restriction. The uses of viscous model gives better optimizations results in optimality requirement. It is needed the uses of inviscid method that forces better physical representation when using viscous correction model