The turbulence structure of convective heat transfer was studied experimentally in complex three-dimensional and separating turbulent boundary layers. Three test cases whose fluid dynamics have been well documented were examined. In case 1, time- and spatially-resolved surface heat transfer was measured in the nose region of a wing-body junction formed by a wing and a flat plate. Both the wing and the endwall were heated and held at a constant uniform temperature 20 °C above ambient temperature. Heat flux rates were increased up to a factor of 3 over the heat flux rates in the approach boundary layer. The rms of the heat flux fluctuations were as high as 25% of the mean heat flux in the vortex-dominated nose region. Away from the wing, upstream of the time-averaged vortex center, augmentation in the heat flux is due to increased turbulent mixing caused by large-scale unsteadiness of the vortex. Adjacent to the wing the augmentation in heat flux is due to a change in the mean velocity field. / Ph. D.

Glioblastoma (GBM) is the most common adult malignant glioma (MG) variant, and the median survival of persons with GBM is about 2 years, even with aggressive treatments. Dogs and humans are the only species in which brain tumors commonly develop spontaneously, with an estimated post-mortem frequency of primary brain tumors approximating 2% in both species. Gliomas represent about 35% of all canine primary brain tumors, with high-grade oligodendroglioma and astrocytoma phenotypes accounting for about 70% of all canine gliomas. Canine gliomas are also treated using surgical, radiotherapeutic, and chemotherapeutic regimens similar to those used in humans. The efficacy of these therapies in dogs with MG is also poor, with median survival times ranging from 3-8 months, which closely mirrors the dismal prognosis associated with human GBM. Thus, treatment of MG represents a current and critically unmet need in both human and veterinary medicine. In this work, we investigate minimally invasive methods to access the brain for the purposes of ultimately improving the diagnosis and treatment of malignant brain tumors. Chapter 1 reviews the current clinical challenges associated with the treatment of GBM, highlights the value of using the spontaneous canine glioma model in translational brain tumor studies, and introduces High-Frequency Irreversible Electroporation (H-FIRE) and Convection Enhanced Delivery (CED), which are two novel treatment platforms for GBM being developed in our lab. In Chapter 2, we demonstrate that definitive diagnosis of brain tumors, a critical first step in patient management, can be safely and accurately performed in dogs with naturally occurring brain tumors using a stereotactic brain biopsy procedure. Chapter 3 evaluates the in vivo safety and biocompatibility of fiberoptic microneedle devices, a major technical component of our convection-enhanced thermotherapy catheter system (CETCS), chronically implanted in the rodent brain. The CETCS is a novel technology being developed and used in our laboratory to improve the delivery of drugs to brain tumors using CED. This study provides regulatory data fundamental to the commercialization of the CETCS device for brain tumor treatment by illustrating that the device did not cause clinically significant neurological complications and resulted in mild pathologic changes in brain tissue, similar to other types of devices designed and approved for use in the brain. In Chapters 4 and 5 we explore possible bystander effects of H-FIRE on glutamate metabolism in the brain. H-FIRE has been shown to be able to both ablate brain tumors as well as disrupt the blood-brain barrier (BBB). As these therapeutic effects of H-FIRE are dependent on applying electrical fields to the tissue that either reversibly permeabilize the cell membrane, allowing treated cells to survive, or permanently disrupt the structure of the cell membrane, causing cell death, we hypothesized that altering the membrane permeability with HFIRE would increase the extracellular glutamate concentrations and contribute to excitotoxic brain tissue damage. Chapters 4 used in vitro brain cell culture systems and in vivo experiments in normal and glioma-bearing rat brains to determine if glutamate release in the brain occurs as a bystander effect following H-FIRE treatment, identify concentrations of glutamate necessary to induce death of cells or BBB disruption, and characterize glutamatergic gene expression in response to H-FIRE treatment. Chapter 5 describes the use of magnetic resonance spectroscopic and spatial transcriptomic methods to further quantify the in vivo effects of H-FIRE treatment on glutamate release and metabolism in dogs with spontaneous brain tumors. The in vitro results indicated that the magnitude of glutamate release following H-FIRE is insufficient to induce cytotoxicity in normal or neoplastic brain cell lines, and also did not increase the permeability of the BBB. In our in vivo model systems, we documented significant, transient post-H-FIRE increases in glutamate to concentrations previously associated with excitotoxicty, with upregulation of the expression of genes involved with ionotropic and metabotropic glutamatergic receptor signaling. A contemporaneous upregulation of genes associated with glutamate uptake and recycling were also noted, indicating an adaptive, protective response to the glutamate release. Our work summarily demonstrates that the diagnosis and potential treatment of malignant brain tumors can be achieved through the use of minimally invasive techniques that provide local access to brain tissue. While complications will always be possible anytime the brain is manipulated surgically, and further investigations are required to characterize the spectrum and mechanisms of adverse events that can occur following CETCS CED and H-FIRE treatment, our results support the continued development of these novel therapeutic platforms for the treatment of GBM. / Doctor of Philosophy / Glioblastoma (GBM) is the most common adult malignant glioma (MG) variant, and the median survival of persons with GBM is about 2 years, even with aggressive treatments. Dogs and humans are the only species in which brain tumors commonly develop spontaneously, with an estimated post-mortem frequency of primary brain tumors approximating 2% in both species. Gliomas represent about 35% of all canine primary brain tumors, with high-grade oligodendroglioma and astrocytoma phenotypes accounting for about 70% of all canine gliomas. Canine gliomas are also treated using surgical, radiotherapeutic, and chemotherapeutic regimens similar to those used in humans. The efficacy of these therapies in dogs with MG is also poor, with median survival times ranging from 3-8 months, which closely mirrors the dismal prognosis associated with human GBM. Thus, treatment of MG represents a current and critically unmet need in both human and veterinary medicine. In this work, we investigate minimally invasive methods to access the brain for the purposes of ultimately improving the diagnosis and treatment of malignant brain tumors. Chapter 1 reviews the current clinical challenges associated with the treatment of GBM, highlights the value of using the spontaneous canine glioma model in translational brain tumor studies, and introduces High-Frequency Irreversible Electroporation (H-FIRE) and Convection Enhanced Delivery (CED), which are two novel treatment platforms for GBM being developed in our lab. In Chapter 2, we demonstrate that definitive diagnosis of brain tumors, a critical first step in patient management, can be safely and accurately performed in dogs with naturally occurring brain tumors using a stereotactic brain biopsy procedure. Chapter 3 evaluates the in vivo safety and biocompatibility of fiberoptic microneedle devices, a major technical component of our convection-enhanced thermotherapy catheter system (CETCS), chronically implanted in the rodent brain. The CETCS is a novel technology being developed and used in our laboratory to improve the delivery of drugs to brain tumors using CED. This study provides regulatory data fundamental to the commercialization of the CETCS device for brain tumor treatment by illustrating that the device did not cause clinically significant neurological complications and resulted in mild pathologic changes in brain tissue, similar to other types of devices designed and approved for use in the brain. In Chapters 4 and 5 we explore possible bystander effects of H-FIRE on glutamate metabolism in the brain. H-FIRE has been shown to be able to both ablate brain tumors as well as disrupt the blood-brain barrier (BBB). As these therapeutic effects of H-FIRE are dependent on applying electrical fields to the tissue that either reversibly permeabilize the cell membrane, allowing treated cells to survive, or permanently disrupt the structure of the cell membrane, causing cell death, we hypothesized that altering the membrane permeability with HFIRE would increase the extracellular glutamate concentrations and contribute to excitotoxic brain tissue damage. Chapters 4 used in vitro brain cell culture systems and in vivo experiments in normal and glioma-bearing rat brains to determine if glutamate release in the brain occurs as a bystander effect following H-FIRE treatment, identify concentrations of glutamate necessary to induce death of cells or BBB disruption, and characterize glutamatergic gene expression in response to H-FIRE treatment. Chapter 5 describes the use of magnetic resonance spectroscopic and spatial transcriptomic methods to further quantify the in vivo effects of H-FIRE treatment on glutamate release and metabolism in dogs with spontaneous brain tumors. The in vitro results indicated that the magnitude of glutamate release following H-FIRE is insufficient to induce cytotoxicity in normal or neoplastic brain cell lines, and also did not increase the permeability of the BBB. In our in vivo model systems, we documented significant, transient post-H-FIRE increases in glutamate to concentrations previously associated with excitotoxicty, with upregulation of the expression of genes involved with ionotropic and metabotropic glutamatergic receptor signaling. A contemporaneous upregulation of genes associated with glutamate uptake and recycling were also noted, indicating an adaptive, protective response to the glutamate release. Our work summarily demonstrates that the diagnosis and potential treatment of malignant brain tumors can be achieved through the use of minimally invasive techniques that provide local access to brain tissue. While complications will always be possible anytime the brain is manipulated surgically, and further investigations are required to characterize the spectrum and mechanisms of adverse events that can occur following CETCS CED and H-FIRE treatment, our results support the continued development of these novel therapeutic platforms for the treatment of GBM.

The convective fluid dynamics and chaos between two parallel plates with temperature discrepancy has been investigated via classic and extended Lorenz system. Both the classic 3-dimensional and extended 5-dimensional Lorenz system are developed by truncating a double Fourier series, which is the solution of the streamline function. Boundary conditions are also considered. The implicit discrete mapping method has been employed to solve the classic and extended Lorenz system, and the motion stability is determined by the eigenvalue analysis. Bifurcation diagram varying with Rayleigh parameter and Prandtl parameter are obtained by solving the stable and unstable period-m motions (m=1,2,4). Symmetric period-1 to asymmetric period-4 motions have been illustrated in the phase space. Therefore, the route from period-1 to period-4 motions to chaos through the period-doubling bifurcation has been demonstrated in the classic and extended Lorenz system. For the extended 5-dimensional Lorenz system, the harmonic frequency-amplitude characteristics are also presented, which provides energy distribution in the parameter space. On bifurcation tree, the non-spiral and spiral homoclinic orbits have been seen and been illustrated in 2-D view and 3-D view. Such homoclinic orbits represent the asymptotic convection steady state that generates the chaos in the convective fluid dynamics. The rich dynamical behaviors of the convective fluid are discovered, and this investigation may help one understand the chaotic dynamics for other thermal convection problems.

Convective cold pools are important modulators of the onset and evolution of deep convection in the tropics. Cold pools are generated by downdrafts and can outlive the storms they originate from to spark new convection. However, most of our understanding of cold pool mechanics comes from high-resolution simulations and a relatively small number of in situ observational studies. This thesis brings novel observational approaches together with climate model data to understand the behavior of cold pools on a global scale and how a mesoscale weather behavior can be accounted for in a climate-scale simulation. First, we leverage a dataset derived from the Advanced Scatterometer (ASCAT) satellite instrument by Garg et al. (2020) to quantify seasonal variations in cold pool activity and their relationship to deep convection across tropical ocean basins. The dataset identifies gradient features (GFs) in the surface wind field, which have been shown to serve as reliable proxies for the boundaries of atmospheric cold pools. We examine the relationship between GFs and climatologies of precipitation, column relative humidity (CRH), and bulk vertical wind shear. We also collocate GFs with precipitation and CRH. High GF frequency, precipitation, and CRH coincide in many regions of the tropics, consistent with our understanding of the physical connections between precipitation and cold pool generation. On the other hand, climatological bulk wind shear is often low in convective regions, and there is a weak inverse correlation between GF frequency and bulk wind shear, while our prior expectation might have been that shear promotes cold pool formation. Compared to GF frequency, GF size shows a weaker relationship with the convective environment, with some of the largest GFs occurring at lower CRH values for a given rainfall rate. In a few exceptional regions and seasons, such as the Indian Ocean in northern hemisphere summer, the region of greatest precipitation does not coincide with the region of greatest GF frequency. These cases also have very high seasonal mean CRH, suggesting that in these regions cold pool formation is suppressed by reduced evaporation of precipitation. Following that, we apply the GF data set to the task of evaluating the realism of the cold pool parameterization in the GISS E3 earth model originally designed by Del Genio et al. (2015). We compare the GF data set to model results from six versions of the GISS model with perturbed parameters. Cold pools generated by the model have significantly different geographic distribution to satellite-observed GFs, particularly in critical convective regions. They also appear to be much less common than GFs, though they have a broadly similar dependence on column water vapor (CWV), especially in terms of size. Finally, we seek to understand the mechanics of the model cold pool parameterization on its own. A subset of high-time resolution model versions is used to deconstruct the behavior of the model parameterization at the scale of individual time steps. Our aim is to see what level of physical realism is associated with the emergent trends seen in the climatological statistics. We find that the model generates cold pool temperature and moisture depressions of similar magnitude to cold pools measured from ships, but tend to dissipate too quickly. Model cold pools also appear to spark increased precipitation, as they are designed to do, but that precipitation appears to come from the stratiform model parameterization, not the moist convection one. Together, these results provide a first opportunity to empirically evaluate a model parameterization originally developed using theory.

Nous analysons les oscillations torsionnelles se développant dans une simulation magnétohydrodynamique de la zone de convection solaire produisant des champs magnétiques de type solaire (champs axisymétriques subissant des inversions de polarités régulières sur des échelles temporelles décadaires). Puisque ces oscillations sont également similaires à celles observées dans le Soleil, nous analysons les dynamiques zonales aux grandes échelles. Nous séparons donc les termes aux grandes échelles (force de Coriolis exercée sur la circulation méridienne et les champs magnétiques aux grandes échelles) de ceux aux petites échelles (les stress de Reynolds et de Maxwell). En comparant les flux de moments cinétiques entre chacune des composantes, nous nous apercevons que les oscillations torsionnelles sont maintenues par l’écoulement méridien aux grandes échelles, lui même modulé par les champs magnétiques. Une analyse d’échange d’énergie confirme ce résultat, puisqu’elle montre que seul le terme comprenant la force de Coriolis injecte de l’énergie dans l’écoulement. Une analyse de la dynamique rotationnelle ayant lieu à la limite de la zone stable et de la zone de convection démontre que celle-ci est fortement modifiée lors du passage de la base des couches convectives à la base de la fine tachocline s’y formant juste en-dessous. Nous concluons par une discussion au niveau du mécanisme de saturation en amplitude dans la dynamo s’opérant dans la simulation ainsi que de la possibilité d’utiliser les oscillations torsionnelles comme précurseurs aux cycles solaires à venir. / We study torsional oscillations developping in a magnetohydrodynamic simulation of the solar convective layers producing solar-like magnetic cycles (large-scale axisymmetric fields subjected to regular polarity reversals). Since these oscillations are similar to those observed in the Sun, we perform an analysis of large-scale zonal dynamics. We separate the large-scale terms (Coriolis force exerted on the meridional circulation and large-scale magnetic fields) from the small-scale contributions (Reynolds and Maxwell stresses). Upon comparing angular momentum fluxes between each of those components, we find that torsional oscillations are driven by the large-scale meridional flow, itself modulated by magnetic fields. An analysis of energy transfers confirms this result, where we see that only the Coriolis force term directly inputs energy in the flow. An analysis of angular momentum fluxes occuring at the interface between the stable and the convective zones shows that the local dynamics therein undergoes a complete shift in going from the base of the convective layers through the base of the thin tachocline developping just beneath it. We conclude by discussing the mechanism of amplitude saturation in the dynamo operating in the simulation and the possibility of using torsional oscillations as precursors to upcoming solar cycles.

On propose traditionnellement que les panaches mantelliques jouent un rôle important dans l'amincissement de la lithosphère. Des données sismologiques sous Hawaïi et Cape Verde suggèrent une limite lithosphère-asthénosphère (LAB) jusqu'à 50 km plus superficielle qu'autour. Des modèles numériques ont montré, en effet, qu'une convection à petite échelle (SSC, pour small-scale convection) dans la couche à faible viscosité formée à la base de la lithosphère par l'accumulation de la matière des panaches peut être un mécanisme efficace d'érosion du manteau lithosphérique. Cependant, ces modèles montrent que, si la plaque se déplace, l'érosion thermo-mécanique de la lithosphère ne dépasse pas 30 km. Afin de mieux étudier les interactions panache/lithosphère, et d'ainsi caractériser les paramètres contrôlant cette érosion, nous avons effectué des simulations numériques en 2D qui utilisent un modèle pétro-thermomécanique basé sur des approches en différences finies associées à des marqueurs actifs. Nous avons focalisé sur : (1) la dynamique de la SSC dans la couche à faible viscosité formée par étalement du panache à la base de la lithosphère et (2) l'effet de la fusion partielle sur cette dynamique. La plaque lithosphérique et le manteau sous-jacent sont caractérisés par une composition péridotitique homogène à viscosité newtonienne dépendante de la température et de la pression. Une vitesse constante, comprise entre 5 et 12,5 cm/an, est imposée au sommet de la plaque. Les panaches sont créés en imposant une anomalie thermique de 150 à 350 K en base du modèle (700 km de profondeur). La fusion partielle est calculée à partir d'un paramétrization des solidus et liquidus pour la fusion anhydre des péridotites. Nous modélisons la déplétion de la péridotite et son effet sur la fusion partielle en supposant que le degré de fusion ne peut qu'augmenter au cours du temps. Le liquide est accumulé jusqu'à un seuil et la masse fondue en excès est extraite instantanément. La rhéologie de la péridotite partiellement fondue est déterminée utilisant une constitutive relation basée sur un modèle de contiguïté, qui permet de prendre en compte les effets de la distribution de matière liquide à l'échelle de grain. La densité varie en fonction du degré de fusion partielle et de la déplétion du résidu solide. Nous analysons la cinématique du panache lors de son interaction avec une plaque mobile, la dynamique de la convection à petite-échelle (SSC) et le rajeunissement thermique de la lithosphère qui en résulte. Le temps de démarrage et la vigueur de la SSC et, par conséquent, le nouvel état d'équilibre thermique de la lithosphère à l'aplomb du panache dépendent du nombre de Rayleigh (Ra) dans la couche instable à la base de la lithosphère, qui est contrôlé par l'anomalie de température et la rhéologie dans cette couche. Pour des panaches chauds et vigoureux, le démarrage de la SSC ne dépend pas de la vitesse de la plaque. Pour des panaches plus faibles, le temps de démarrage diminue avec l'augmentation de la vitesse de la plaque. Ce comportement est expliqué par une différence dans la structure thermique de la lithosphère, due à des échanges diffusifs à la base lithosphère plus efficaces pour des panaches lents. La diminution de la viscosité associée à la présence de magma et la diminution de la densité du résidu solide accélèrent le démarrage et accroissent la vigueur de la SSC, entraînant une érosion plus efficace et plus proche du point d'impact de panache sous la lithosphère. / Mantle plumes are traditionally proposed to play an important role in thinning the lithosphere. Seismic images beneath Hawaii and Cape Verde, for instance, show a lithosphere-asthenosphere boundary (LAB) up to 50 km shallower than the surroundings. However, previous numerical modeling of plume-lithosphere interaction implies that unless the plate is stationary the thermo-mechanical erosion of the lithosphere does not exceed 30 km. We used 2D petrological-thermo-mechanical numerical models based on a finite-difference method on a staggered grid and marker in cell method to further study the plume-lithosphere interaction. We focused on: (1) analyzing the dynamics of the small-scale convection (SSC) in the plume wake as a function of the plume vigor and plate velocity and (2) quantifying the effect of partial melting on this SSC. A homogeneous peridotite composition with a Newtonian temperature- and pressure-dependent viscosity is used to simulate both the plate and the convective mantle. A constant velocity, ranging from 5 to 12.5 cm/yr, is imposed at the top of the plate. Plumes are created by imposing a thermal anomaly of 150 to 350 K on a 50 km wide domain at the base of the model (700 km depth); the plate right above the thermal anomaly is 40 Myr old. Partial melting is modeled using the batch-melting solidus and liquidus in anhydrous conditions. We model the progressive depletion of peridotite and its effect on partial melting by assuming that the melting degree only strictly increases through time. Melt is accumulated until a porosity threshold is reached and the excess melt is instantaneously extracted. The rheology of the partially molten peridotite is determined using a viscous constitutive relationship based on a contiguity model, which enables to take into account the effects of grain-scale melt distribution. The density varies as a function of the melt fraction and of the depletion of the residue. We analyze the kinematics of the plume as it impacts a moving plate, the dynamics of time-dependent small-scale convection (SSC) instabilities developing in the low-viscosity layer formed by spreading of hot plume material at the lithosphere base, and the resulting thermal rejuvenation of the lithosphere. The onset time and the vigor of SSC and, hence, the new equilibrium thermal state of the lithosphere atop the plume wake depends on the Rayleigh number (Ra) in the unstable layer at the base of the lithosphere, which is controlled by the temperature anomaly and rheology in the plume-fed layer. For vigorous, hot plumes, SSC onset times do not depend on plate velocity. For more sluggish plumes, SSC onset times decrease with increasing plate velocity. This behavior is explained by differences in the thermal structure of the lithosphere, due to variations in the spreading behavior of the plume material at the lithosphere base. Reduction of the viscosity in partial molten domains and decrease in density of the depleted residuum accelerate and enhance the vigor of small-scale convection in the plume-fed low-viscosity layer at the lithosphere base. It also reduces SSC onset times, leading to more effective erosion closer to the plume-lithosphere impact.

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.

Le séchage des boues d'épuration est un problème environnemental actuel, qui n'est pas suffisamment décrit dans la littérature. Par conséquent, ce travail représente une étude numérique des transferts de chaleur et de masse lors du séchage solaire des boues d’épuration. Cette boue est assimilée à un milieu poreux et exposée à un écoulement laminaire de convection forcée à l'intérieur d'un canal horizontal. Les transferts dans le canal et le milieu poreux sont décrits respectivement par les équations classiques de la convection forcée et par le modèle de Darcy-Brinkman-Forchheimer. Une méthode implicite aux différences finies est utilisée pour discrétiser le système d'équations différentielles régissant les transferts. Les systèmes algébriques obtenus sont résolus en utilisant les algorithmes de Gauss, Thomas et Gauss-Seidel. Afin de déterminer la vitesse de séchage, nous associons à ces équations un modèle de cinétique de séchage. Ce modèle est basé sur le concept de la courbe caractéristique. Nous avons particulièrement étudié les effets des conditions climatiques et des conditions relatives à la boue sur les évolutions spatio-temporelles des nombres caractéristiques des transferts ainsi que sur la cinétique de séchage. Le travail est complété par des simulations en utilisant des données météorologiques réelles de la région de Tataouine au sud de la Tunisie. Ces données ont subi un traitement statistique à l’aide de la méthode de Liu et Jordan afin de déterminer la journée type de chaque mois. L’étude de rentabilité du séchoir a montré que la période estivale est la période optimale pour le séchage. / The drying of sewage sludge is a current environmental problem, not sufficiently described in the literature. Hence, the aim of this work is a numerical study of heat and mass transfers during solar drying of residual sludge. This sludge is assimilated to a porous medium and exposed to a forced convection laminar flow within a horizontal channel. The transfers in the channel and the porous medium are respectively described by the classic equations of forced convection and the Darcy-Brinkman-Forchheimer model. The implicit finite difference method is used to discretize the governing differential equation system. The algebraic systems obtained are solved using the Gauss, Thomas and Gauss-Seidel algorithms. To determine the drying rate, we associate a drying kinetics model. This model is based on the concept of the characteristic curve. We particularly studied the effects of climatic conditions (temperature, velocity and relative humidity of the ambient air as well as the solar radiation intensity) and the conditions relating to the sludge on the spatio-temporal evolutions of the transfers characteristic numbers as well as on drying kinetics. This work is completed by simulations using meteorological data from the Tataouine region in southern Tunisia. These data were statistically processed using the Liu and Jordan method to determine the typical day of each month. The rentability study of the dryer show that the summer period is the optimum period for drying.

Ce travail concerne une étude expérimentale du comportement hygrothermique de matériaux bio-sourcés sous la forme de briques de terre comprimée (BTC) et de briques de terre stabilisée (BTS). Nous avons déterminé les propriétés thermo-physiques et les isothermes de sorption de ces matériaux et évalué l'influence de l'ajout de stabilisants chimiques (ciment et chaux), sur leurs conductivités thermiques et leurs capacités hygroscopiques. Cette étude est complétée par une modélisation et une simulation numérique des transferts de chaleur et de masse dans une cavité ventilée dont l'une des parois verticales est composée de BTC. Les transferts hygrothermiques dans la paroi, assimilée à un milieux poreux, et dans la cavité ventilée sont décrits respectivement par le modèle de Luikov et les équations classiques de la convection mixte. Ces équations de transferts sont résolues par une méthode implicite aux différences finie, la méthode itérative de Gauss-Seidel et l'algorithme de Thomas. Nous avons analysé l'influence de la température, de l'humidité relative et de la vitesse de l'air ambiant, la densité du flux de chaleur appliqué sur la face externe de la paroi ainsi que la nature du matériau bio-sourcé sur les transferts hygrothermiques dans cette paroi et l'écoulement d'air dans la cavité. Les résultats montrent que la stabilisation chimique augmente la conductivité thermique de la BTC et réduit sa capacité de sorption. L'accroissement de la densité du flux de chaleur appliqué sur la face externe de la paroi de BTC provoque une augmentation des transferts de chaleur par mode latent et sensible entre la face interne de cette paroi et l'air qui s'écoule dans la cavité. / This work concerns an experimental study of the hygrothermal behavior of compressed earth bricks (CEB) and stabilized earth bricks (SEB). We determined its thermo-physical properties and sorption isotherms and evaluated the impact of the chemical stabilizers (cement and lime) addition on their thermal conductivities and hygroscopic capacities. This study is complemented by a modeling and numerical simulations of heat and mass transfers in a ventilated cavity one of its vertical walls is composed of CEB. The heat an mass transfers in this wall, assimilated to a porous medium, and in the ventilated cavity are respectively described by the Luikov model and the mixed convection equations. The transfer equations are solved using an implicit finite difference method, the Gauss–Seidel method and the Thomas algorithm. We have analyzed the effects on the heat and mass transfers within this wall and in the cavity of the temperature and relative humidity air, the inlet air velocity in the cavity and the heat flux density applied on the external face of the vertical wall composed of CEB. These results show that chemical stabilization increase the thermal conductivity of CEB and leads to a reduction in moisture sorption capacity. The increase of the heat flux density applied to the external face of the wall composed of CEB leads to an augmentation of the latent and sensible heat transfers between the inner face of this wall and the air flowing in the cavity.

Concevoir des dispositifs thermiques plus compacts, nécessitant moins de masse de matière, produisant moins de pertes de charge et présentant un rendement thermique accru représente un enjeu clé pour des performances améliorées à un coût moindre. La présente thèse étudie le potentiel et la validité de l’optimisation topologique en tant qu’outil CFD viable permettant de générer des designs thermiques optimaux par rapport aux approches conventionnelles telles que l’optimisation de forme et paramétrique. La première partie de la thèse présente une étude expérimentale de structures bi matériaux arborescentes optimales obtenues par optimisation topologique. Le problème mathématique d’optimisation topologique est formulé et implémenté dans OpenFOAM®. Il est appliqué au problème d’optimisation de la conduction thermique dans une configuration de type volume-vers-point. Des mesures thermiques expérimentales sont effectuées sur les structures optimisées, en utilisant la thermographie infrarouge afin de quantifier leurs performances de transfert de chaleur et ainsi validé les performances des structures optimales déterminées par le code d’optimisation topologique développé. La deuxième partie de la thèse présente une technique bi-objectif innovante d’optimisation topologique des systèmes de transferts de chaleur conjugués (CHT, Conjugate Heat Transfer) en régimes d’écoulement laminaires. Pour cela, le problème est développé mathématiquement et implémenté dans le solveur OpenFOAM® basé sur une méthode directe par volumes finis. La fonction objectif est formulée par la pondération linéaire de deux fonctions objectifs, l’une pour la réduction de la perte de charge et l’autre pour l’augmentation du transfert de chaleur. Ceci représente une cible très difficile du point de vue numérique en raison de la concurrence entre les deux objectifs (minimisation de la perte de charge et maximisation de la puissance thermique récupérable). Des designs non intuitifs, mais optimaux au sens de Pareto, ont été obtenus, analysés, discutés et justifiés à l’aide de diverses méthodes d’analyses numériques globale et locale. De plus, une configuration identique à une optimisation par une méthode Lattice Boltzmann issue de la bibliographie a été optimisée en utilisant le solveur OpenFOAM® développé. L’objectif, en complément de la comparaison des solutions optimales, est également d’initier un cas de référence pour les futures études dans ce domaine de recherche et d’innovation de façon à pouvoir pleinement comparer les solutions optimales obtenues par différences méthodes et différents solveurs. Enfin, les différents points expérimentaux et numériques mis en lumière et illustrés dans cette thèse démontrent l’importance de la méthodologie et potentiel très important de l’optimisation topologique pour la conception de systèmes thermiques industriels plus performants. / Designing thermal devices that are more compact with less mass, less frictional losses and increased thermal efficiency is a key requirement for enhanced performances at a lower cost. The present PhD thesis investigates the potential and validity of topology optimization numerical method as a viable CFD tool to generate optimal thermal designs as compared to conventional approaches like shape and parametric optimization. The first part of the thesis presents an experimental investigation of topology optimized tree-like structures made of two materials. The topolgy optimization mathematical problem is formulated and implemented in OpenFOAM®. It is applied to the topolgy optimization problem of volume-to-point heat removal. Experimental thermal measurements are carried out, on the optimal structures, using infrared thermography in order to quantify their heat transfer performances and thus validate the performances of the optimal structures determined by the developed topology optimization code. The second part of the thesis presents an innovative bi-objective optimization technique for topology optimization of Conjugate Heat Transfer (CHT) systems under laminar flow regimes. For that purpose, an inequality constrained bi-objective topology optimization problem is developed mathematically and implemented inside the Finite Volume based OpenFOAM® solver. The objective function is formulated by linear combination of two objective functions for pressure drop reduction and heat transfer enhancement which is numerically a very challenging task due to a competition between the two objectives (minimization of pressure drop and maximization of recoverable thermal power). Non-intuitive Pareto-optimal designs were obtained, analyzed, discussed and justified with the help of various global and local numerical analysis methods. Additionally, a recent Lattice Boltzmann topology optimization problem form the literature was solved using the developed OpenFOAM® solver. The objective, in addition to the comparison of the optimal solutions, is also to initiate a case of reference for future studies in this field of research and innovation so as to be able to fully compare the optimal solutions obtained by different and different methods. solvers. Finally, the various experimental and numerical findings highlighted and illustrated in this PhD thesis, demonstrate the importance of the methodology and immense potential behind topology optimization method for designing efficient industrial thermal systems.