De nombreuses applications industrielles mettent en jeu des écoulements gaz-particules, comme les turbines aéronautiques et les réacteurs a lit fluidisé de l'industrie chimique. La prédiction des propriétés de la phase dispersée, est essentielle à l'amélioration et la conception des dispositifs conformément aux nouvelles normes européennes des émissions polluantes. L'objectif de cette these est de développer le formalisme Euler- Lagrange dans un solveur parallèle et non-structuré pour la simulation aux grandes échelles pour ce type d'écoulements. Ce travail est motivé par l'augmentation rapide de la puissance de calcul des machines massivement parallèles qui ouvre une nouvelle voie pour des simulations qui étaient prohibitives il y a une décennie. Une attention particulière a été portée aux structures de données afin de conserver une certaine simplicité et la portabilité du code sur des differentes! architectures. Les développements sont validés pour deux configurations : un cas académique de turbulence homogène isotrope décroissante et un calcul polydisperse d'un jet turbulent recirculant chargé en particules. L'équilibrage de charges de particules est mis en évidence comme une solution prometteuse pour les simulations diphasiques Lagrangiennes afin d'améliorer les performances des calculs lorsque le déséquilibrage est trop important. / Particle-laden flows occur in industrial applications ranging from droplets in gas turbines tofluidized bed in chemical industry. Prediction of the dispersed phase properties such as concentration and dynamics are crucial for the design of more efficient devices that meet the new pollutant regulations of the European community. The objective of this thesis is to develop an Euler-Lagrange formulation on a parallel and unstructured solver for large- eddy simulation. This work is motivated by the rapid increase in computing power which opens a new way for simulations that were prohibitive one decade ago. Special attention is taken to keep data structure simplicity and code portability. Developments are validated in two configurations : an academic test of a decaying homogeneous isotropic turbulence and a polydisperse two-phase flow of a confined bluff body. The use of load-balancing capabilities is highlighted as a promising solut! ion in Lagrangian two-phase flow simulations to improve performance when strong imbalance of the dispersed phase is present

Les écoulements décollés sont fortement instationnaires, l'objectif de cette thèse a été de localiser et d'identifier les phénomènes à la source de ces instationnarités et de comprendre les processus physiques permettant le transfert de l'information de ces zones sources au reste de l'écoulement. Pour ce faire une analyse des résultats issus de simulations numériques a été réalisée. En étudiant la corrélation et la cohérence entre les positions de choc et les fluctuations de pression, l'interaction a pu être séparée en plusieurs parties distinctes. A l'aide de la théorie des caractéristiques définissant les directions et les cinématiques de propagation de l'information, les liens spatio-temporels entre ces différentes régions ont pu être déterminés. Les résultats de ces études couplés avec ceux issus des expériences ont montré clairement que les phénomènes se produisant à l'intérieur de la zone de recirculation existant en aval du choc de décollement gouvernent la dynamique de la totalité de l'interaction, aussi bien à basse fréquence qu'à moyenne fréquence. Ainsi les mouvements de choc apparaissent comme le miroir des phénomènes se produisant à l'intérieur de la zone décollée. Une représentation équivalente en fluide non visqueux permettant une description du comportement instationnaire de l'interaction a aussi été proposée. / Separated flow are often strongly unsteady; the aim of this thesis is to localize and identify the sources of the unsteadiness and to understand the physical phenomena governing the information transfer from these source zones to the rest of the flow. To do this, data used for this analysis have been obtained from numerical simulations (LES). Both cross-correlation and coherence between shock motion and pressure fluctuations have shown that the interaction can be split in several distinct zones. The theory of characteristics is used to define the information paths and the propagation velocities, so that the space-time links between these regions have been determined. Both numerical and experimental studies have clearly shown that phenomena present within the recirculation buble govern the whole of the interaction, at low and intermediate frequencies. Indeed the shock motions appears as the mirror of phenomena present in the separated zone. An inviscid equivalent scenario has been proposed to represent the interaction.

<div>Studies of turbulent combustion in the past mainly focus on problems with single-regime combustion. In practical combustion systems, however, combustion rarely occurs in a single regime, and different regimes of combustion can be observed in the same system. This creates a significant gap between our existing knowledge of combustion in single regime and the practical need in multi-regime combustion. In this work, we aim to extend the traditional single-regime combustion models to problems involving different regimes of combustion. Among the existing modeling methods, Transported Probability Density Function (PDF) method is attractive for its intrinsic closure of treating detailed chemical kinetics and has been demonstrated to be promising in predicting low-probability but practically important combustion events like local extinction and re-ignition. In this work, we focus on the model assessment and advancement of the Large Eddy Simulation (LES)/ PDF method in predicting turbulent multi-regime combustion.</div><div><br></div><div><div>Two combustion benchmark problems are considered for the model assessment. One is a recently designed turbulent piloted jet flame that features statistically transient processes, the Sydney turbulent pulsed piloted jet flame. A direct comparison of the predicted and measured time series of the axial velocity demonstrates a satisfactory prediction of the flow and turbulence fields of the pulsed jet flame by the employed LES/PDF modeling method. A comparison of the PLIF-OH images and the predicted OH mass fraction contours at a few selected times shows that the method captures the different combustion stages including healthy burning, significant extinction, and the re-establishment of healthy burning, in the statistically transient process. The temporal history of the conditional PDF of OH mass fraction/temperature at around stoichiometric conditions at different axial locations suggests that the method predicts the extinction and re-establishment timings accurately at upstream locations but less accurately at downstream locations with a delay of burning reestablishment. The other test case is a unified series of existing turbulent piloted flames. To facilitate model assessment across different combustion regimes, we develop a model validation framework by unifying several existing pilot stabilized turbulent jet flames in different combustion regimes. The characteristic similarity and difference of the employed piloted flames are examined, including the Sydney piloted flames L, B, and M, the Sandia piloted flames D, E, and F, a series of piloted premixed Bunsen flames, and the Sydney/Sandia inhomogeneous inlet piloted jet flames. Proper parameterization and a regime diagram are introduced to characterize the pilot stabilized flames covering non-premixed, partially premixed, and premixed flames. A preliminary model assessment is carried out to examine the simultaneous model performance of the LES/PDF method for the piloted jet flames across different combustion regimes.</div><div><br></div><div>With the assessment work in the above two test cases, it is found that the LES/PDF method can predict the statistically transient combustion and multi-regime combustion reasonably well but some modeling limitations are also identified. Thus, further model advancement is needed for the LES/PDF method. In this work, we focus on two model advancement studies related to the molecular diffusion and sub-filter scale mixing processes in turbulent combustion. The first study is to deal with differential molecular diffusion (DMD) among different species. The importance of theDMD effects on combustion has been found in many applications. However, in most previous combustion models equal molecular diffusivity is assumed. To incorporate the DMD effects accurately, we develop a model called Variance Consistent Mean Shift (VCMS) model. The second model advancement focuses on the sub-filter scale mixing in high-Karlovitz (Ka) number turbulent combustion. We analyze the DNS data of a Sandia high-Ka premixed jet flame to gain insights into the modeling of sub-filter scale mixing. A sub-filter scale mixing time scale is analyzed with respect to the filter size to examine the validity of a power-law scaling model for the mixing time scale.</div></div>

Les matériaux absorbants acoustiques, qui sont d’un intérêt stratégique en aéronautique pour la diminution passive du bruit des réacteurs d’avion, conduisent à une physique complexe où l’écoulement turbulent, des ondes acoustiques, et l’absorbant interagissent. Cette thèse porte sur la simulation de cette interaction dans le problème modèle d’un écoulement de canal turbulent avec des parois impédantes, par le biais de simulations numériques aux grandes échelles implicites, dans un contexte de calcul haute performance.Une étude est d’abord faite des grandes échelles dans un canal turbulent avec des parois rigides, en s’intéressant plus particulièrement à l’effet d’une faible compressibilité (Mach <3) sur les caractéristiques de ces échelles.Un canal turbulent avec une paroi de type impédance est ensuite simulé, avec une condition habituelle de périodicité dans le sens de l’écoulement. On observe que pour des faibles valeurs de la résistance et des fréquences de résonance basses, l’écoulement est instable, ce qui engendre une onde le long de l’absorbant, qui modifie la turbulence et augmente la trainée.Enfin, on se tourne vers une simulation de canal spatial en levant la condition de périodicité dans la direction de l’écoulement, ce qui permet d’introduire une onde acoustique en entrée de domaine. L’atténuation de l’onde dans l’écoulement turbulent est étudiée avec des parois rigides, puis un absorbant acoustique est introduit. Dans cette configuration plus réaliste, il est confirmé que l’écoulement peut devenir instable au bord amont de l’absorbant, ce qui empêche l’atténuation de l’onde acoustique incidente. / Acoustic liners are a key technology in aeronautics for the passive reduction of the noise generated by aircraft engines. They are employed in a complex flow scenario in which the acoustic waves, the turbulent flow, and the acoustic liner are interacting.During this thesis, in a context of high performance computing, a compressible Navier-Stokes solver has been developed to perform implicit large eddy simulations of a model problem of this interaction: a turbulent plane channel flow with one wall modeled as an impedance condition.As a preliminary step the wall-turbulence in rigid channel flows and associated large-scale motions are investigated. A straightforward algorithm to detect these flow features is developed and the effect of compressibility on the flow structures and their contribution to the drag are studied. Then, the interaction between the acoustic liner and turbulent flow is investigated assuming periodicity in the streamwise direction. It is shown that low resistance and low resonance frequency tend to trigger flow instability, which modifies the conventional wall-turbulence and also results in drag increase.Finally, the simulation of a spatial channel flow was addressed. In this case no periodicity is assumed and an acoustic wave can be injected at the inlet of the domain. The effect of turbulence on sound attenuation is studied without liner, before a liner is introduced on a part of the channel bottom wall. In this more realistic case, it is confirmed that low resistance acoustic liners trigger an instability at the leading edge of the liner, resulting in drag increase and excess noise generation.

Le procédé de craquage thermique est un procédé industriel sensible aux conditions de température et de pression. L’utilisation de réacteurs aux parois nervurées est une méthode permettant d’améliorer la sélectivité chimique du procédé en augmentant considérablement les transferts de chaleur. Cependant, cette méthode induit une augmentation des pertes de charge dans le réacteur, ce qui est dommageable pour le rendement chimique et doit être quantifié. En raison de la complexité de l’écoulement turbulent et de la cinétique chimique, le gain réel offert par ces géométries en termes de sélectivité chimique est toutefois mal connu et difficile à estimer, d’autant plus que des mesures expérimentales détaillées sont très rares et difficiles à mener. L’objectif de ce travail est double: d’une part évaluer le gain réel des parois nervurées sur le rendement chimique; d’autre part proposer de nouveaux designs de réacteurs offrant une sélectivité chimique optimale. Ceci est rendu possible par l’approche de simulation numérique aux grandes échelles (LES), qui est utilisée pour étudier l’écoulement réactif à l’intérieur de diverses géométries de réacteurs. Le code AVBP, qui résout les équations de Navier Stokes compressibles pour les écoulements turbulents, est utilisé pour simuler le procédé grâce à une méthodologie numérique adaptée. En particulier, les effets des pertes de charge et du transfert thermique sur la conversion chimique sont comparés pour un réacteur lisse et un réacteur nervuré afin de quantifier l’impact de la rugosité de paroi dans des conditions d’utilisation industrielles. Une méthodologie d’optimisation du design des réacteurs, basée sur plusieurs simulations numériques et les processus Gaussiens, est finalement mise au point et utilisée pour aboutir à un design de réacteur de craquage thermique innovant, maximisant le rendement chimique / Thermal cracking is an industrial process sensitive to both temperature and pressure operating conditions. The use of internally ribbed reactors is a passive method to enhance the chemical selectivity of the process, thanks to a significant increase of heat transfer. However, this method also induces an increase in pressure loss, which is damageable to the chemical yield and must be quantified. Because of the complexity of turbulence and chemical kinetics, and as detailed experimental measurements are difficult to conduct, the real advantage of such geometries in terms of selectivity is however poorly known and difficult to assess. This work aims both at evaluating the real benefits of internally ribbed reactors in terms of chemical yields and at proposing innovative and optimized reactor designs. This is made possible using the Large Eddy Simulation (LES) approach, which allows to study in detail the reactive flow inside several reactor geometries. The AVBP code, which solves the Navier-Stokes compressible equations for turbulent flows, is used in order to simulate thermal cracking thanks to a dedicated numerical methodology. In particular, the effect of pressure loss and heat transfer on chemical conversion is compared for both a smooth and a ribbed reactor in order to conclude about the impact of wall roughness in industrial operating conditions. An optimization methodology, based on series of LES and Gaussian process, is finally developed and an innovative reactor design for thermal cracking applications, which maximizes the chemical yield, is proposed

Des bâtiments de grande hauteur sont construits avec un poids et un amortissement structurel de plus en plus faibles en lien avec l'évolution des techniques de construction et des matériaux. La connaissance des charges de vent dynamiques est un enjeu important pour la conception des grands bâtiments afin de garantir leur sécurité structurelle. L'objectif de cette thèse est d’évaluer la capacité de la simulation numérique des grandes échelles (LES) à prédire les charges de vent sur les structures et d’étudier l'influence des conditions d’entrée d’une simulation LES sur ces charges. Des expériences ont été menées à échelle réduite dans la soufflerie atmosphérique NSA du CSTB afin de documenter l’écoulement atmosphérique modélisé, de caractériser son interaction avec un bâtiment et les charges de vent statiques et dynamiques résultantes. Le sillage du bâtiment a été caractérisé grâce à des mesures PIV. Les efforts globaux et les pressions locales ont été mesurés par une balance et des prises de pression à haute fréquence. Ces expériences en soufflerie ont permis de développer un générateur de conditions amont (GCA) pour la simulation LES, visant à reproduire les principales caractéristiques de la turbulence dans la couche limite. La base de données constituée a également permis de qualifier les résultats des simulations LES réalisées avec le code OpenFOAM dans la configuration de l’expérience. L’utilisation du nouveau GCA et d’un générateur dégradé qui ne respecte pas toutes les caractéristiques de l'écoulement a permis de montrer la nécessité de bien reproduire les caractéristiques du vent incident pour accéder aux charges dynamiques sur le bâtiment. / High-rise buildings are built with increasingly low weight and structural damping in relation to the evolution of construction techniques and materials. The understanding of dynamic wind loads is an important issue for the design of high-rise buildings in order to guarantee their structural safety. The objective of the present work is to assess the ability of large eddy simulation (LES) to predict wind loads on structures and to investigate the influence of the inflow boundary conditions of a LES simulation on these loads. Experiments were carried out at a small scale in the NSA atmospheric wind tunnel of CSTB to document the modeled atmospheric boundary layer, to characterize its interaction with a building and the resulting static and dynamic wind loads. The wake flow around the building has been characterized by PIV measurements. Global and local wind loads were measured by a high frequency force balance and high frequency pressure taps. These wind tunnel experiments allowed for the development of an inflow turbulence generator for the LES simulation,which was aimed at reproducing the main characteristics of turbulence in the boundary layer. The database also made it possible to assess the quality of the results of the LES simulations carried out with the OpenFOAM code in the same configuration as the experiment. The use of both the new turbulence generator and a degraded one that does not account for all the characteristics of the flow has made it possible to show the necessity to reproduce the characteristics of the upstream wind flow in order to access the dynamic wind loads on the building.

Este trabalho tem como principal objetivo o desenvolvimento de um método numérico para simulação das grandes escalas de escoamentos turbulentos tridimensionais utilizando uma modelagem de turbulência baseada em filtragem temporal (denominada TLES - Temporal Large Eddy Simulation). O método desenvolvido combina discretizações temporais com ordem de mínima precisão 2 (Adams-Bashforth, QUICK, Runge-Kutta), um método de projeção de ordem 2, com discretizações espaciais também de ordem 2 obtidas pelo método de volumes finitos. Esta metodologia foi empregada na simulação de problemas teste turbulentos como o canal e a cavidade impulsionada, sendo este último resultado simulado pela primeira vez com modelagem TLES. Os resultados mostram uma excelente concordância quando comparado com resultados de simulações diretas (DNS) e dados experimentais, superando resultados clássicos obtidos com formulação LES com filtragem espacial. / The main objective of this work is to develop a numerical method for large eddy simulation of tridimensional turbulent flows using a model based on temporal filtering (TLES - Temporal Large Eddy Simulation). The developed method combines at least 2nd order temporal discretizations (Adams-Bashforth, QUICK, Runge-Kutta), a 2nd order projection method, and 2nd order spatial discretizations obtained by the finite volume method. This methodology was employed to the simulation of turbulent benchmark problems such as channel and lid-driven cavity flows. The latter is simulated for the first time using a TLES turbulence modelling. Results show excellent agreement when compared to Direct Numerical Simulations (DNS) and experimental data, with better results than classical results produced by standard LES formulation with spatial filtering.

O projeto de pesquisa propôs avaliar a metodologia de Simulação de Escalas Adaptativas (SAS) para descrever escoamentos turbulentos e não-reativos utilizando estudos de casos característicos, amplamente documentados, os quais possuem comportamentos do escoamento distintos presentes em diferentes regiões de uma câmara de combustão. O primeiro estudo de caso foi a análise do escoamento sobre um degrau, em que foi avaliada a capacidade do modelo Simulação de Escalas Adaptativas, frente aos modelos de Navier-Stokes com Média de Reynolds (RANS) e Simulação de Grandes Escalas (LES) e aos dados experimentais, em prever a distribuição de pressão, ponto de recolamento e de perfis de velocidade ao longo do domínio após a separação. Pode-se notar que o modelo SAS apresentou resultados praticamente idênticos aos resultados obtidos pelo modelo RANS com relação à distribuição de pressão e a posição ponto de recolamento. Porém, os perfis de velocidade apresentaram algumas discrepâncias com relação aos perfis de velocidade dos modelos RANS e LES e dos resultados experimentais. Um segundo estudo de caso foi a análise do escoamento através de um turbilhonador, em que a capacidade do modelo SAS foi avaliada, comparando seus resultados com os resultados do modelo de Navier-Stokes Não-Estacionárias com Média de Reynolds (URANS) e com os dados experimentais, em prever perfis de velocidade em regiões de recirculação presentes neste estudo de caso. Pode-se observar que ambos os modelos conseguiram prever as principais estruturas de recirculação do escoamento, porém, os perfis de velocidade apresentaram significativas discrepâncias com relação aos dados experimentais. Em seguida, foram feitas comparações entre os modelos SAS e URANS com relação à previsão da precessão central de vórtice e de estruturas de vórtices, das quais foi observado que o modelo SAS apresenta uma maior capacidade para prever estas estruturas em relação ao modelo URANS. / The research project aimed to evaluate the Scale-Adaptive Simulation (SAS) methodology to describe turbulent and non-reactive flows using characteristic, widely documented, case studies, which have distinct flow behaviors present in different regions of a chamber of combustion. The first case study was the analysis of a flow over a backward-facing step, from which the Scale-Adaptive Simulation (SAS) model capacity was evaluated, compared to the Reynolds Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) models and experimental data, in order to predict the pressure distribution, reattachment point and velocity profiles throughout the domain after separation. It can be noticed that the SAS model presented results almost identical to the results obtained by the RANS model in relation to the pressure distribution and reattachment position. However, the velocity profiles presented some discrepancies in respect to RANS and LES velocity profiles and the experimental results. A second case study was the analysis of the flow through a swirler, from which the capacity of the SAS model was evaluated, comparing its results to the results of the Unsteady Reynolds Averaged Navier-Stokes (URANS) model and with the experimental data, to predict velocity profiles in recirculation regions present in this case study. It can be observed that both models were able to predict the main recirculation structures of the flow, however, the velocity profiles presented significant discrepancies in relation to the experimental data. Then, comparisons were made between the SAS and URANS models in respect to the prediction of vortex precession vortex core and vortex structures, from which it was observed that the SAS model presents a greater capacity to predict these structures in relation to the URANS model.

Submitted by PPG Engenharia e Tecnologia de Materiais (engenharia.pg.materiais@pucrs.br) on 2018-06-05T13:28:29Z No. of bitstreams: 1 frantz2018simulacoes.pdf: 23131075 bytes, checksum: e748910d1820968a07c86be9461b7489 (MD5) / Approved for entry into archive by Sheila Dias (sheila.dias@pucrs.br) on 2018-06-12T12:40:17Z (GMT) No. of bitstreams: 1 frantz2018simulacoes.pdf: 23131075 bytes, checksum: e748910d1820968a07c86be9461b7489 (MD5) / Made available in DSpace on 2018-06-12T12:49:08Z (GMT). No. of bitstreams: 1 frantz2018simulacoes.pdf: 23131075 bytes, checksum: e748910d1820968a07c86be9461b7489 (MD5) Previous issue date: 2018-03-09 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / This work investigates the method of large-eddy simulation (LES) in the context of gravity currents, which is found necessary since it allows a substantial increase in the order of magnitude of the characteristic Reynolds number used in numerical simulations, approaching them with natural scales, in addition to significantly reducing the computational cost. The implicit large eddy simulation (ILES) methodology, based on the spectral vanishing viscosity model, is unprecedentedly employed in the context of gravity currents, is compared against with explicit methods such as the static and dynamic Smagorisnky. The evaluation of the models is performed based on statistics from a direct numerical simulation (DNS). Results demonstrate that the first model based purely on numerical dissipation, introduced by means of the second order derivative, generates better correlations with the direct simulation. Finally, experimental cases of the literature, in different flow configurations, are reproduced numerically showing good agreement in terms of the front position evolution. / Este trabalho investiga o m?todo de simula??o de grandes escalas (LES) no contexto de correntes gravitacionais. O mesmo se faz necess?rio, visto que possibilita um aumento substancial da ordem de grandeza do n?mero de Reynolds caracter?stico utilizado em simula??es num?ricas, aproximando os mesmos de escalas naturais, al?m de reduzir significativamente o custo computacional dos c?lculos. A avalia??o dos modelos ? realizada utilizando uma base de dados de simula??o num?rica direta (DNS). A metodologia de simula??o de grandes escalas impl?cita (ILES), baseada no modelo de viscosidade turbulenta espectral, ? colocado a prova de maneira in?dita no contexto de correntes de gravidade com m?todos expl?citos dispon?veis na literatura. Resultados demonstram que o mesmo, baseado puramente em dissipa??o num?rica introduzida por meio do comportamento dos esquemas de derivada de segunda ordem, gera melhores correla??es com as estat?sticas baseadas em campos m?dios da simula??o direta. Por fim, casos experimentais da literatura, em diferentes configura??es de escoamento, s?o reproduzidos numericamente.

Neste trabalho foi realizado um estudo utilizando os modelos de turbulência Simulação das Grandes Escalas, Large Eddy Simulation (LES), e Simulação dos Vórtices Desprendidos, Detached Eddy Simulation (DES), para simular o escoamento compressível interno em um duto contendo válvulas controladoras na saída dos gases de combustão de um reator de craqueamento catalítico fluido, com o objetivo de comparar o desempenho numérico e computacional de ambas as técnicas. Para isso foi utilizado um programa comercial de dinâmica dos fluidos computacional, Computational Fluid Dynamics (CFD), que possui em seu código os dois modelos de turbulência. / In the present work a study was conducted using Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models in order to simulate the internal compressible flow in a duct containing the flue gas discharge control valves of a fluid catalytic cracking reactor so as to compare the numerical and computational behavior of both techniques. A commercial Computational Fluid Dynamics (CFD) software, which includes these turbulence models in its code, was used.