Depuis plusieurs décennies déjà, l'industrie aérospatiale tente de repousser les limites du possible, avec des véhicules de plus en plus légers, mais qui voyagent à des vitesses de plus en plus élevées. Pour ce faire, des recherches dans le domaine des régimes d'écoulement hypersonique ont été effectuées pour mieux comprendre le comportement des fluides lorsque soumis à ces régimes d'écoulement. Cependant, pour effectuer le design de véhicules voyageant dans ces régimes d'écoulement, les interactions entre le fluide et les structures doivent être prises en compte. Il est bien connu [1; 2], que différents types d'interactions prennent place dans ces situations aérothermoélastiques, telles que des interactions force-déplacement, des interactions thermiques fluide-structure et possiblement des interactions thermochimiques. Toutes ces interactions doivent donc être prises en compte pour dresser un portrait global du comportement d'une section ou de l'ensemble d'un véhicule hypersonique. Ce mémoire a donc pour objectifs d'investiguer les phénomènes d'interaction fluide, structure et thermique (FSTI) dans un contexte d'écoulement hypersonique. Plus spécifiquement, une méthodologie de couplage multiphysique a été développée pour résoudre des problèmes aérothermoélastiques en grande déformation. La méthodologie de couplage développée est basée sur une approche partitionnée avec un couplage itératif. Ces objectifs présentent un point de vue intéressant étant donné que l'étude des cas aérothermoélastiques en grandes déformations ne semble pas, selon la revue de la littérature, avoir été explorée. Les recherches présentées dans ce mémoire tentent donc d'étudier cette voie en proposant une méthodologie de simulation numérique. De plus, à titre de contribution supplémentaire des outils numériques ont été implémentés dans une librairie maison du logiciel OpenFOAM®. Ce logiciel libre de droit facilitera la reproduction et la distribution des outils et des simulations qui sont présentées dans ce document. Le contenu de ce mémoire se divise en trois sections. Dans un premier temps, les phénomènes physiques qui sont impliqués dans ces écoulements ont été modélisés individuellement. Des modèles mathématiques sont présentés et des modèles numériques ont été validés pour s'assurer de l'implémentation adéquate des programmes. Par la suite, un environnement modulaire de simulation multiphysique sous l'environnement OpenFOAM est présenté. Cet environnement permet l'intégration de différents solveurs physiques pour solutionner différentes régions physiques dans un contexte de simulation FSI, FSTI ou d'échauffement aérodynamique. Les interactions entre les différentes régions sont gérées via des conditions limites d'interface spécifiquement conçues. De plus, un algorithme de couplage itératif basé sur une approche partitionnée est également utilisé. Cette section mettra l'accent sur l'implémentation de la méthodologie de couplage avec le logiciel OpenFOAM et les contributions pour la communauté d'utilisateurs du logiciel. Pour finir, la méthodologie de couplage multiphysique a été validée en effectuant des simulations d'interaction FSTI simples présentées dans la littérature. De plus, des simulations aérothermoélastiques complexes présentant des phénomènes de grandes déformations sont également analysées. / For several decades, the aerospace industry tries to improve their knowledge over the science of flight, to create vehicles that are lighter, but that can sustain faster speed regimes. Lately, research in the field of hypersonic flow allowed a better understanding of the fluid physics while sustaining those flow regimes. However, to design vehicles that are able to sustain these flow regimes, the interactions between the fluid and the structure must be considered. It is well known [1; 2] that several interaction phenomena will occur with those aerothermoelastic problems, such as force-displacement interactions, fluid-structure thermal interactions and in some cases thermochemical interactions. These interactions must be evaluated to understand the behaviour of a part or the overall hypersonic vehicle. The objective of this thesis is to investigate fluid, structure and thermal interactions (FSTI) phenomena for hypersonic flow regimes. More specifically, a multiphysic coupling method was developed to model aerothermoelastic problem by taking into consideration large structural deformation. The coupling methodology is based on the partitioned approach with an iterative coupling. These objectives present an interesting approach because the study of aerothermoelastic problems involving large structural deformation has not been explored, based on the literature review that was conducted for this thesis. Thus, the study of these physical phenomena will be presented in this research by proposing a numerical coupling strategy. Moreover, simulation tools were also developed using the OpenFOAM® environment. This open-source software will facilitate the reproduction and distribution of tools and simulations that are presented in this document. The thesis is divided in three sections. First, several physics that constitute the behaviour of the aerothermoelastic problematic will be modelled individually. Mathematical models will be presented and numerical models will be validated to ensure that the implementation of the code generate adequate results. Also, a modular framework for multiphysic simulation developed using OpenFOAM framework will be presented. This framework allows the integration of several physical solvers to modelled multiple physical regions for FSI, FSTI and aerodynamic heating problems. Interaction between regions are handled through specifically designed interfaces boundary conditions. An iterative coupling algorithm based on a partitioned approach is also used. This section will be focused on the implementation of the framework for OpenFOAM and the contribution for its community. In the last section, the coupling methodology will be validated with FSTI simulations. Moreover, simulations of more complexes aerothermoelastic problems will also be presented. Large deformation for those aerothermoelastic problems will also be evaluated with these last simulations.

Depuis plusieurs décennies déjà, l'industrie aérospatiale tente de repousser les limites du possible, avec des véhicules de plus en plus légers, mais qui voyagent à des vitesses de plus en plus élevées. Pour ce faire, des recherches dans le domaine des régimes d'écoulement hypersonique ont été effectuées pour mieux comprendre le comportement des fluides lorsque soumis à ces régimes d'écoulement. Cependant, pour effectuer le design de véhicules voyageant dans ces régimes d'écoulement, les interactions entre le fluide et les structures doivent être prises en compte. Il est bien connu [1; 2], que différents types d'interactions prennent place dans ces situations aérothermoélastiques, telles que des interactions force-déplacement, des interactions thermiques fluide-structure et possiblement des interactions thermochimiques. Toutes ces interactions doivent donc être prises en compte pour dresser un portrait global du comportement d'une section ou de l'ensemble d'un véhicule hypersonique. Ce mémoire a donc pour objectifs d'investiguer les phénomènes d'interaction fluide, structure et thermique (FSTI) dans un contexte d'écoulement hypersonique. Plus spécifiquement, une méthodologie de couplage multiphysique a été développée pour résoudre des problèmes aérothermoélastiques en grande déformation. La méthodologie de couplage développée est basée sur une approche partitionnée avec un couplage itératif. Ces objectifs présentent un point de vue intéressant étant donné que l'étude des cas aérothermoélastiques en grandes déformations ne semble pas, selon la revue de la littérature, avoir été explorée. Les recherches présentées dans ce mémoire tentent donc d'étudier cette voie en proposant une méthodologie de simulation numérique. De plus, à titre de contribution supplémentaire des outils numériques ont été implémentés dans une librairie maison du logiciel OpenFOAM®. Ce logiciel libre de droit facilitera la reproduction et la distribution des outils et des simulations qui sont présentées dans ce document. Le contenu de ce mémoire se divise en trois sections. Dans un premier temps, les phénomènes physiques qui sont impliqués dans ces écoulements ont été modélisés individuellement. Des modèles mathématiques sont présentés et des modèles numériques ont été validés pour s'assurer de l'implémentation adéquate des programmes. Par la suite, un environnement modulaire de simulation multiphysique sous l'environnement OpenFOAM est présenté. Cet environnement permet l'intégration de différents solveurs physiques pour solutionner différentes régions physiques dans un contexte de simulation FSI, FSTI ou d'échauffement aérodynamique. Les interactions entre les différentes régions sont gérées via des conditions limites d'interface spécifiquement conçues. De plus, un algorithme de couplage itératif basé sur une approche partitionnée est également utilisé. Cette section mettra l'accent sur l'implémentation de la méthodologie de couplage avec le logiciel OpenFOAM et les contributions pour la communauté d'utilisateurs du logiciel. Pour finir, la méthodologie de couplage multiphysique a été validée en effectuant des simulations d'interaction FSTI simples présentées dans la littérature. De plus, des simulations aérothermoélastiques complexes présentant des phénomènes de grandes déformations sont également analysées. / For several decades, the aerospace industry tries to improve their knowledge over the science of flight, to create vehicles that are lighter, but that can sustain faster speed regimes. Lately, research in the field of hypersonic flow allowed a better understanding of the fluid physics while sustaining those flow regimes. However, to design vehicles that are able to sustain these flow regimes, the interactions between the fluid and the structure must be considered. It is well known [1; 2] that several interaction phenomena will occur with those aerothermoelastic problems, such as force-displacement interactions, fluid-structure thermal interactions and in some cases thermochemical interactions. These interactions must be evaluated to understand the behaviour of a part or the overall hypersonic vehicle. The objective of this thesis is to investigate fluid, structure and thermal interactions (FSTI) phenomena for hypersonic flow regimes. More specifically, a multiphysic coupling method was developed to model aerothermoelastic problem by taking into consideration large structural deformation. The coupling methodology is based on the partitioned approach with an iterative coupling. These objectives present an interesting approach because the study of aerothermoelastic problems involving large structural deformation has not been explored, based on the literature review that was conducted for this thesis. Thus, the study of these physical phenomena will be presented in this research by proposing a numerical coupling strategy. Moreover, simulation tools were also developed using the OpenFOAM® environment. This open-source software will facilitate the reproduction and distribution of tools and simulations that are presented in this document. The thesis is divided in three sections. First, several physics that constitute the behaviour of the aerothermoelastic problematic will be modelled individually. Mathematical models will be presented and numerical models will be validated to ensure that the implementation of the code generate adequate results. Also, a modular framework for multiphysic simulation developed using OpenFOAM framework will be presented. This framework allows the integration of several physical solvers to modelled multiple physical regions for FSI, FSTI and aerodynamic heating problems. Interaction between regions are handled through specifically designed interfaces boundary conditions. An iterative coupling algorithm based on a partitioned approach is also used. This section will be focused on the implementation of the framework for OpenFOAM and the contribution for its community. In the last section, the coupling methodology will be validated with FSTI simulations. Moreover, simulations of more complexes aerothermoelastic problems will also be presented. Large deformation for those aerothermoelastic problems will also be evaluated with these last simulations.

Les essais expérimentaux pour des écoulements hypersoniques sont extrêmement dispendieux dans les coûts des installations et d'opérations. Par contre, la meilleure façon de contourner ce problème est l'utilisation de simulation numérique pour représenter des systèmes complexes. Cependant, la simulation numérique est encore à ces débuts et il reste beaucoup de travail à accomplir pour bien comprendre la physique de la mécanique des fluides. Ainsi, la plupart des scientifiques n'ont pas le choix de se retourner vers des modèles analytiques plus simples, afin de résoudre des problèmes complexes. Ce mémoire traite d'une méthode semi-analytique et semi-numérique afin de caractériser la modélisation, l'analyse et l'optimisation d'un véhicule hypersonique, utilisant un système de propulsion de type superstatoréacteur (SSRéacteur) ou superstatoréacteur à combustion induite par ondes de choc (SSCRéacteur), pour une mission donnée. Chaque véhicule hypersonique est un surfeur d'ondes (anglais : waverider) en 2D et qui est composé d'un modèle d'entrée d'air, de mixage et de réaction air/carburant, de chambre de combustion, de tuyère, d'aérodynamique externe et de masse. Ainsi, tous ces sous-systèmes utilisent un écoulement à propriétés constantes et/ou variables en fonction de la température et ils sont interreliés dans le but d'analyser les performances du véhicule global. Par l'emploi d'un processus d'optimisation, les performances des véhicules sont évaluées pour une convergence sur une masse déterminée (430 kg) et sur un équilibre des forces en Xet Ten fonction d'une mission donnée (Mach 7 à 20). La synthèse des résultats obtenus convient que pour les paramètres de la mission définie, les deux configurations ont des portées similaires, et que le SSCRéacteur a un fort potentiel avec l'utilisation de la détonation comme processus de combustion. Ces résultats donnent une bonne approximation des performances plausibles de deux configurations génériques de SSRéacteur et de SSCRéacteur. Cette étude multidisciplinaire démontre bien que des études complémentaires sont requises pour l'obtention de propriétés optimales (l'impulsion spécifique et la portée) pour chaque concept et ceci à chacune des conditions de vol. Néanmoins, le concept du SSCRéacteur demeure toujours très prometteur pour les années futures.

Tunable diode laser absorption spectroscopy using an external cavity diode laser operating in the infra-red has been developed to monitor CO2 in the freestream of the Longshot hypervelocity facility at the Von Karman Institute for Fluid Dynamics. The Longshot facility offers a unique European facility for ground testing and numerical validation applications, however, some of the traditional data rebuilding aspects are in question. A non-intrusive absorption<p>sensor could significantly aid in improving the knowledge of freestream static values thereby improving the models used in data rebuilding and numerical simulation. The design of such a sensor also expands the spectroscopic capabilities of the Von Karman Institute.<p><p>The absorption sensor is designed around the single P12 (00001)-(30013) rovibrational transition near 1.6µm (6218.09cm-1 specifically) which yields relatively weak direct absorption levels at about 3.5% per meter for typical Longshot freestream conditions. However, when handled carefully, adequate signal-to-noise can be acquired to exploit significant flow information. By being able to operate in this range, total sensor cost can be easily an a factor of two or more cheaper than sensors designed for the deeper infrared. All sensor elements were mounted to a compact portable optics bench utilizing single-mode optical fibers to allow for quick installation at different facilities by eliminating tedious optical realigning. Scans at 600Hz were performed over 20ms of the 40ms test time to extract core static temperature, pressure and velocity.<p><p>These results are compared with the current state of the Longshot data rebuild method. The non-uniform flow properties of the shear layer and test cabin rested gas accumulation was of an initial concern. The temperature and density gradients along with significant radial velocity components could result in DLAS temperature, pressure and velocity that are significantly different than that of the target freestream inviscid core values. Fortunately, with the proper selection of the P12 rotational number, this effect could be more or less ignored as the higher temperature and lower density gas of this region is relatively transparent.<p><p>Ultimately, acquired temperature and density were moderately accurate when compared to Longshot rebuilt results owing primarily to the baseline extraction which poses issues for such low absorption signals. However, the extracted velocity data are quite accurate. This is a definite puls for the sensor as the freestream enthalpy of cold hypersonic facilities is dictated primarily by the kinetic energy contribution. Being able to compare velocity gives insight to the level of vibration non-equilibrium in the flow. The velocity of the DLAS and the Longshot rebuild are quite close. This adds more weight to the argument that vibrational excitation is very low (if present at all) in the free stream and that the van de derWaals equation of state usage and constant specific heat assumption might be an adequate model for the data rebuild after all. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Laminar turbulent transition is known for a long time as a critical phenomenon influencing the thermal load encountered by hypersonic vehicle during their planetary re-entry trajectory. Despite the efforts made by several research laboratories all over the world, the prediction of transition remains inaccurate, leading to oversized thermal protection system and dramatic limitations of hypersonic vehicles performances. One of the reasons explaining the difficulties encountered in predicting transition is the wide variety of parameters playing a role in the phenomenon. Among these parameters, surface roughness is known to play a major role and has been investigated in the present thesis.<p><p>A wide bibliographic review describing the main parameters affecting transition and their coupling is proposed. The most popular roughness-induced transition predictions correlations are presented, insisting on the lack of physics included in these methods and the difficulties encountered in performing ground hypersonic transition experiments representative of real flight characteristics. This bibliographic review shows the importance of a better understanding of the physical phenomenon and of a wider experimental database, including real flight data, for the development of accurate prediction methods.<p><p>Based on the above conclusions, a hypersonic experimental test campaign is realized for the characterization of the flow field structure in the vicinity and in the wake of 3D roughness elements. This fundamental flat plate study is associated with numerical simulations for supporting the interpretation of experimental results and thus a better understanding of transition physics. Finally, a model is proposed in agreement with the wind tunnel observations and the bibliographic survey.<p><p>The second principal axis of the present study is the development of a hypersonic in-flight roughness-induced transition experiment in the frame of the European EXPERT program. These flight data, together with various wind tunnel measurements are very important for the development of a wide experimental database supporting the elaboration of future transition prediction methods. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Boundary-layer transition from a laminar to a turbulent regime is a critical driver in the design of high-speed vehicles. The aerothermodynamic loads associated with transitional or fully turbulent hypersonic boundary layers are several times higher than those associated with laminar flow. The presence of isolated roughness elements on the surface of a body can accelerate the growth of incoming disturbances and introduce additional instability mechanisms in the flow field, eventually leading to a premature occurrence of transition. This dissertation studies the instabilities induced by three-dimensional discrete roughness elements located inside a high-speed boundary layer developing on a flat plate. Two-dimensional local linear stability theory (2D-LST) is employed to identify the instabilities evolving in the three-dimensional flow field that characterizes the wake induced by the roughness elements and to investigate their evolution downstream. A formulation of the disturbance energy evolution equation available for base flows depending on a single spatial direction is generalized for the first time to base flows featuring two inhomogeneous directions and perturbations depending on three spatial directions. This generalization allows to obtain a decomposition of the temporal growth rate of 2D-LST instabilities into the different contributions that lead to the production and dissipation of the total disturbance energy. This novel extension of the formulation provides an additional layer of information for understanding the energy exchange mechanisms between a three-dimensional base flow and the perturbations resulting from 2D-LST. Stability computations for a calorically perfect gas illustrate that the wake induced by the roughness elements supports the growth of different sinuous and varicose instabilities which coexist together with the Mack-mode perturbations that evolve in the flat-plate boundary layer, and which become modulated by the roughness-element wake. A single pair of sinuous and varicose disturbances is found to dominate the wake instability in the vicinity of the obstacles. The application of the newly developed decomposition of the temporal growth rate reveals that the roughness-induced wake modes extract most of their potential energy from the transport of entropy fluctuations across the base-flow temperature gradients and most of their kinetic energy from the work of the disturbance Reynolds stresses against the base-flow velocity gradients. Further downstream, the growth rate of the wake instabilities is found to be influenced by the presence of Mack-mode disturbances developing on the flat plate. Strong evidence is observed of a continuous synchronization mechanism between the wake instabilities and the Mack-mode perturbations. This phenomenon leads to an enhancement of the amplification rate of the wake modes far downstream of the roughness element, ultimately increasing the associated integrated amplification factors for some of the investigated conditions. The effects of vibrational molecular excitation and chemical non-equilibrium on the instabilities induced by a roughness element are studied for the case of a high-temperature boundary layer developing on a sharp wedge configuration. For this purpose, a 2D-LST solver for chemical non-equilibrium flows is developed for the first time, featuring a fully consistent implementation of the thermal and transport models employed for the base flow and the perturbation fields. This is achieved thanks to the automatic derivation and implementation tool (ADIT) available within the von Karman Institute extensible stability and transition analysis (VESTA) tool-kit, which enables an automatic derivation and implementation of the 2D-LST governing equations for different thermodynamic flow assumptions and models. The stability computations for this configuration show that sinuous and varicose disturbances also dominate the wake instability in the presence of vibrational molecular energy mode excitation and chemical reactions. The resulting base-flow cooling associated with the modeling of such high-temperature phenomena is found to have opposite stabilizing and destabilizing effects on the streamwise evolution of the sinuous and varicose instabilities. The modeling of vibrational excitation and chemical non-equilibrium acting exclusively on the perturbations is found to have a stabilizing influence in all cases. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Aviation industry is continuously growing especially for very long distance flights due to the globalisation of local economies around the world and the explosive economic growth in Asia. Reducing the time of intercontinental flights from 16-20 hours to 4 hours or less would therefore make the, already booming, ultra-long distance aviation sector even more attractive. To accomplish this drastic travel time reduction for civil transport, hypersonic cruise aircraft are considered as a potential cost-effective solution. Such vehicles should also be fuelled by liquid hydrogen, which is identified as the only viable propellant to achieve antipodal hypersonic flight with low environmental impact. Despite considerable research on hypersonic aircraft and hydrogen fuel, several major challenges should still be addressed before such airliner becomes reality. The current thesis is therefore motivated by the potential benefit of hydrogen-fuelled hypersonic cruise vehicles associated with their limited state-of-the-art.Hypersonic cruise aircraft require innovative structural configurations and thermal management solutions due to the extremely harsh flight environment, while the uncommon physical properties of liquid hydrogen, combined with high and long-term heat fluxes, introduce complex design and technological storage issues. Achieving hypersonic cruise vehicles is also complicated by the multidisciplinary nature of their design. In the scope of the present research, appropriate methodologies are developed to assess, design and optimize the thermo-structural model and the cryogenic fuel tanks of long-range hydrogen-fuelled hypersonic civil aircraft. Two notional vehicles, cruising at Mach 5 and Mach 8, are then investigated with the implemented methodologies. The design analysis of light yet highly insulated liquid hydrogen tanks for hypersonic cruise vehicles indicates an optimal gravimetric efficiency of 70-75% depending on insulation system, tank wall material, tank diameter, and flight profile. A combination of foam and load-bearing aerogel blanket leads to the lightest cryogenic tank for both the Mach 5 and the Mach 8 aircraft. If the aerogel blanket cannot be strengthened sufficiently so that it can bear the full load, then a combination of foam and fibrous insulation materials gives the best solution for both vehicles. The aero-thermal and structural design analysis of the Mach 5 cruiser shows that the lightest hot-structure is a titanium alloy construction made of honeycomb sandwich panels. This concept leads to a wing-body weight of 143.9 t, of which 36% accounts for the wing, 32% for the fuselage, and 32% for the cryogenic tanks. As expected, hypersonic thermal loads lead to important weight penalties (of more than 35%). The design of the insulated cold structure, however, demonstrates that the long-term high-speed flight of the airliner requires a substantial thermal protection system, such that the best configuration (obtained by load-bearing aerogel blanket) leads to a titanium cold design of only 4% lighter than the hot structure. Using aluminium 7075 rather than titanium offers a further weight saving of about 2%, resulting in a 135.4 t wing-body weight (with a contribution of 23%, 25%, 18% and 34% from the TPS, the wing, the fuselage, and the cryogenic tanks respectively). Given the design hypotheses, the difference in weight is not significant enough to make a decisive choice between hot and cold concepts. This requires the current methodologies to be further elaborated by relaxing the simplifications. Investigation of the thermal protection must be extended from one single point to different regions of the vehicle, and the TPS thickness and weight should be considered in the structural sizing of the cold design. More generally, the design process should be matured by including additional (static, dynamic and transient) loads, special structural concepts, multi-material configurations and other parameters such as cost and safety aspects. / Doctorat en Sciences de l'ingénieur et technologie / This thesis was conducted in co-tutelle between University of Sydney and Université Libre de Bruxelles.Professor Dries Verstraete was my supervisor at the University of Sydney (so as a member of SydneyUni), but is automatically registered here as a member of ULB because he worked at ULB almost ten years ago.Ben Thornber is also a member of the University of Sydney but the application does not save it for an unknown reason. / info:eu-repo/semantics/nonPublished

The numerical modelling of the VKI-Longshot facility remains a challeng-ing task as it requires multi-physical numerical methods in order to simulate all the components. In the current dissertation, numerical tools were developed in order to study each component of the facility separately and a deep investigations of each stage of the shot were performed. This helped to better understand the different processes involved in the flow development inside this hypersonic wind tunnel. However the numerical computation of different regions of the facility treated as independent from each others remains an approximation at best.The accuracy of the rebuilding code for determining the free stream conditions and the total enthalpy in the VKI-Longshot facility was investigated by using a series of unsteady numerical computations of axisymmetric hypersonic flow over a heat flux probe. Good agreement was obtained between the numerical results and the measured data for both the stagnation pressure and the heat flux dur- ing the useful test time.The driver-driven part of the Longshot facility was modelled using the quasi one-dimensional Lagrangian solver L1d2. The three main conditions used for the experiments —low, medium and high Reynolds number —were considered.The chambrage effect due to the junction between the driver and the driven tubes in the VKI-Longshot facility was investigated. The computation showed great ben- efit of the chambrage in increasing the speed of the piston and thus the final compression ratio of the test gas.Two dimensional simulations of the flow in the driver and the driven tube were performed using Arbitrary Lagrangian Eulerian (ALE) solver in COOLFLuiD. A parallel multi-domain strategy was developed in order to integrate the moving piston within the computational domain.The computed pressure in the reservoir is compared to the one provided by the experiment and good agreement was obtained for both con- editions.Finally, an attempt was made to compute the starting process of the flow in the contoured nozzle. The transient computation of the flow showed how the primary shock initiates the flow in the nozzle before reaching the exit plan at time of 1.5 [ms] after the diaphragm rupture. The complex interactions of the reflected shocks in the throat raise the temperature above 9500 [K] which was not expected. Chemical dissociation of Nitrogen was not taken into account during this transient investigation which may play a key role considering the range of temperature reached near the throat. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

<p align="justify">Cette thèse traite de l'étude numérique et expérimentale du transport et de la déposition d'aérosols dans les poumons. La partie numérique du travail porte sur des simulations uni-, bi- et tridimensionnelles du comportement des aérosols dans la structure pulmonaire. Les simulations unidimensionnelles (1D) sont effectuées dans des modèles trompettes et multibranche similaires à ceux utilisés dans les études de transport et de mélange gazeux dans les poumons. Le dépôt total, le profil des dépôts le long des différentes générations de l'arbre bronchique ainsi que la dispersion de boli d'aérosols sont calculés en fonction de la taille des particules et du protocole respiratoire. Un bolus consiste en un faible volume d'aérosols inhalé sous la forme d'un pic de concentration au cours d'une inspiration d'air pur. Les résultats montrent les limitations intrinsèques liées aux modèles 1D quant à la description du transport des aérosols dans les poumons et suggèrent l'utilisation d'équations multidimensionnelles pour décrire le transport de particules. Des simulations bidimensionnelles (2D) sont alors développées pour décrire le comportement des aérosols dans un modèle représentatif de la zone alvéolaire du poumon humain. Les simulations montrent que les particules ne se déposent pas uniformément sur les parois alvéolaires des conduits mais qu'elles sont principalement localisées près de l'entrée des alvéoles et ceci principalement dans le cas de petites particules (diamètre inférieure à 0.5 mm). De plus, les résultats montrent que le traditionnel coefficient de dispersion utilisé dans l'approche unidimensionnelle ne peut pas être extrapolé dans la zone alvéolaire du poumon.</p><p><p align="justify">Finalement, des simulations tridimensionnelles (3D) sont réalisées dans un modèle d'un conduit pulmonaire entouré d'alvéoles et confirment la déposition largement hétérogène des aérosols calculée dans l'étude bidimensionnelle suggérant que les concentrations locales et moyennes en aérosols peuvent être substantiellement différentes.</p><p><p align="justify">Parallèlement, des données expérimentales de déposition totale et de dispersion de boli d'aérosols sont obtenues et comparées aux résultats numériques. Des indices tels que la dispersion du bolus expiré, la déposition totale ou le déplacement du mode entre les courbes de concentration des boli inspiré et expiré mesurés au niveau de la bouche ont été évalués. Des simulations numériques similaire aux tests expérimentaux sont également effectuées. Bien qu'une approche relativement simplifiée soit utilisée, il apparaît que les simulations décrivent raisonnablement bien les résultats expérimentaux.</p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished