This work is focused on the development of a hybrid DSMC/CFD solver to examine hypersonic boundary layer flow over discrete surface roughness. The purpose of these investigations is to identify and quantify the non-equilibrium effects that influence the roughness-induced disturbance field and surface quantities of interest for engineering applications. To this end, a new hybrid framework is developed for high-fidelity hybrid solutions involving five-species air hypersonic boundary layer flow applications. A novel approach is developed for DSMC particle generation at a hybrid interface for gas mixtures with internal degrees of freedom. The appropriate velocity distribution function is formulated in the framework of Generalized Chapman-Enskog Theory, and includes contributions from species mass diffusion, shear stress and heat fluxes (both translational and internal) on the perturbation of the equilibrium distribution function. This formulation introduces new breakdown parameters for use in hybrid DSMC/CFD applications, and the new sampling algorithm allows for the generation of DSMC internal energies from the appropriate non-equilibrium distribution for the first time in the literature. The contribution of the internal heat fluxes to the overall perturbation is found to be of the same order as the stress tensor components, underscoring the importance of DSMC particle generation from the Generalized Chapman-Enskog distribution. A detailed comparison of the transport coefficients is made between the DSMC and CFD solvers, and a general best-fit approach is developed for the consistent treatment of diffusion, viscosity and thermal conductivity for a five-species air gas mixture. The DSMC VHS/VSS model parameters are calibrated through an iterative fitting approach using the Nelder-Mead Simplex Algorithm. The VSS model is found to provide the best fit (within 5% over the temperature range) to the transport models used in the CFD solver. The best-fit five-species air parameters are provided for general use by the DSMC community, either for hybrid applications or to provide improved consistency in general DSMC/CFD applications. This hybrid approach has been applied to examine hypersonic boundary layer flow over discrete surface roughness for a variety of roughness geometries and flow conditions. An (asymmetric) elongated hump geometry and (symmetric) diamond shaped roughness geometry are examined at high and low altitude conditions. Detailed comparisons among the hybrid solution and the CFD no-slip and slip wall solutions were made to examine the differences in surface heating, translational/vibrational non-equilibrium in the flow near the roughness, and the vortex structures in the wake through the Q-criterion. In all cases examined, the hybrid solution predicts a lower peak surface heating to the roughness compared to either CFD solution, and a higher peak surface heating in the wake due to vortex heating. The observed differences in vortex heating are a result of the predicted vortex structures which are highlighted using the Q-criterion. The disturbance field modeled by the hybrid solution organizes into a system of streamwise-oriented vortices which are slightly stronger and have a greater spanwise extent compared to the CFD solutions. As a general trend, it was observed that these differences in the predicted heating by the hybrid and CFD solutions increase with increasing Knudsen number. This trend is found for both peak heating values on the roughness and in the wake. / text

Soot is formed whenever the combustion of hydrocarbon fuels is incomplete. Since soot particles are very small, they can be inhaled and cause severe health problems, such as pulmonary diseases. They can also cause environmental pollution, and have a significant effect on global warming and melting of polar ice sheets. The environmental and health impact of soot depends strongly on soot particle size and morphology, so there is a pressing need for measuring techniques that characterize aerosolized soot. Laser-Induced incandescence (LII) has proved to be a reliable technique for making spatial and temporal measurements of soot primary particle sizes and soot volume fractions. Nevertheless, there are some unresolved issues in LII, which may cause large errors in soot primary particle size inferred from LII data. One of these issues is anomalous cooling, which is the unexpectedly high initial rate of soot particle cooling observed in experiments, which can not be predicted by LII models. Among the speculations about the possible causes of this phenomenon is the transient gas dynamics effects which have been ignored in LII models. Another phenomena that has been speculated to affect LII predictions in high fluence LII, is how the gas dynamics of sublimed carbon clusters impact the local gas dynamics surrounding the particle during the cooling phase. The focus of this thesis is to investigate transient effects on heat conduction in low fluence LII, and the gas dynamics of sublimed species in high fluence LII using Direct Simulation Monte Carlo (DSMC) method. DSMC is a statistical/numerical method which works based on the physics of Boltzmann equation. In this method a large number of real molecules are represented by the so called simulated molecules and the state of these molecules is tracked during the simulation as they undergo collisions with each other and with the boundaries. The results show that transient effects contribute to anomalous cooling but are not the only cause of this phenomenon. The time scale over which transient effects are significant is also found to be very close to that of anomalous cooling which implies the real cause of anomalous cooling has some similarities to transient effects. Also regarding gas dynamics of sublimation, two effects in particular have been investigated using DSMC, namely, back flux of sublimed species and formation of shock waves. DSMC results confirm the back flux of sublimed species but no shock wave was observed for the boundary conditions considered in this study.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24611号 / 工博第5117号 / 新制||工||1978(附属図書館) / 京都大学大学院工学研究科航空宇宙工学専攻 / (主査)教授 大和田 拓, 教授 髙田 滋, 講師 杉元 宏 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Nous présentons dans cette thèse une adaptation de la technique de vélocimétrie par marquage moléculaire (MTV) aux micro-écoulements gazeux. Les effets de luminescence de l’acétone gazeuse excitée par un rayonnement UV, mis en jeu dans la MTV, ont été analysés en vue d’une application en vélocimétrie à basse pression. La phosphorescence de l’acétone diminue fortement avec la pression, pour devenir non détectable à des pressions de l’ordre du kPa. En revanche, la fluorescence reste détectable à des pressions de l’ordre de la dizaine de Pa. L’analyse des déplacements de molécules luminescentes au sein de l’écoulement porteur a montré que les effets de la diffusion moléculaire sont importants et augmentent avec la raréfaction du gaz. Une méthode de reconstruction, basée sur l’équation d’advection diffusion, a été développée. Elle permet d’extraire le profil de vitesse à partir de l’analyse du déplacement et de la déformation de la zone marquée, en prenant en compte la diffusion des molécules luminescentes. L’analyse d’un écoulement de Poiseuille dans un canal de section rectangulaire et de dimensions millimétriques, sous des pressions de l’ordre de 100 kPa, a montré la capacité de la MTV à extraire avec précision la vitesse locale en écoulements confinés, lorsque la méthode de reconstruction est appliquée. Une feuille de route pour l’analyse future par MTV des écoulements raréfiés, notamment dans le régime glissant, est finalement proposée. / In the present thesis we present an adaptation of Molecular Tagging Velocimetry (MTV) to gas microflows. The photo-luminescence effects of gaseous acetone excited by UV light, implemented in MTV, have been analyzed in various pressure conditions. The acetone phosphorescence shows a drastic decrease with pressure and becomes non measurable for pressures lower than 1 kPa. On the other hand, fluorescence shows a slower decrease and remains clearly detectible at pressures as low as 10 Pa. The motion of tracer molecules within the carrier flow has been studied. The analysis of the displacement of the tagged molecules has shown the strong influence of molecular diffusion, this influence being increased with the gas rarefaction. A reconstruction method based on the advection-diffusion equation has been developed. It allows to extract the velocity profile from the analysis of the displacement and deformation of the tagged region, taking into account the diffusion of tracer molecules. This reconstruction method has been successfully implemented to analyse a Poiseuille flow in a rectangular millimetric channel, under atmospheric pressure conditions, and the capability of MTV to accurately extract the local velocity in confined gas flows has been demonstrated. Finally, some short term perspectives have been proposed with the aim to help achieving rarefied flows analysis by MTV.

Very Low Earth Orbit (VLEO) provides many benefits for space missions, including better image resolution for Earth observation, better telecommunication link with ground stations, lower launch cost, lower risk of collisions, and fast end-of-life disposal. The last point in benefit is also the main challenge for placing satellites in VLEO. Being so close to the Earth’s surface, with mean orbital altitude below 450 km, there’s still a significant amount of atmospheric particles left in VLEO, which causes drag force. A spacecraft operating in VLEO will de-orbit within months or even less if the drag force is not compensated. Atmosphere-Breathing Electric Propulsion (ABEP) is a potential solution for this challenge. An ABEP system comprises an atmospheric particle intake and an Electric Propulsion (EP) system. The intake collects particles and delivers them to the electric thruster’s Discharge Channel (DC), the EP system then ionizes the particles and accelerates them out to generate thrust. The ABEP design by Institute of Space Systems (IRS) at the University of Stuttgart has been ongoing, where various design concepts for the intake were studied, and the specular intake design has been selected for further investigation. Subsequent simulations at IRS showed stagnation and backflow inside the new specular intake, with increased intake length and frontal diameter. So, for this thesis, Direct Simulation Monte Carlo (DSMC) simulations were performed for the specular intake to investigate its geometry sensitivity. It was found that due to high particle thermal velocities in the VLEO, the collection coefficient (intake collection ability) decreases with the increase in intake length. And in combination with the drag analysis of the specular intake, it was concluded that, for a specular intake with a DC diameter of 37 mm, the optimum intake length is below one meter. / VLEO ger många fördelar för rymduppdrag vilket inkluderar bättre bildupplösning för observation av jorden, bättre telekommunikation med markstationer, lägre uppskjutningskostnad, lägre risk för kollisioner och för att snabbt komma ur omloppsbana. Den sista fördelen är för utmaningen att placera satelliter i VLEO. Eftersom det är så nära jordens yta finns det fortfarande en signifikant mängd luftmolekyler kvar i omgivningen, vilket orsakar motstånds. En rymdfarkost som verkar i VLEO kommer att gå ur omloppsbanan inom några månader eller inom kortare tid, om motståndskraften inte kompenseras. ABEP är en potentiell lösning för denna utmaning. Ett ABEP-system består av ett luftmolekylintag och ett elektriskt framdrivningssystem. Intaget samlar in luftmolekyler och ledar dem till urladdningskanal. Det elektriska framdrivningssystem joniserar sedan luftpartiklarna och accelererar sedan ut dem för att genera dragkraft. ABEP-designen av IRS i University of Stuttgart har vart pågående och det fanns flera förslag för luftintaget. Den bästa intagsdesignen, som kallas ”specular intake”, valdes och undersöktes ytterligare. Påföljande simuleringar visade att det finns stagnationsflöde och ”backflow” inuti det nya intaget, med ökad diameter och intagslängd. I detta examensarbete utfördes DSMC-simuleringar för specular intake för att undersöka geometrins känslighet. Det visade sig att på grund av termiska partikelhastigheter i VLEO minskar collection coefficient (intagsuppsamlingsförmågan) med ökningen av intagslängden. Tillsammans med luftmotståndsanalysen för specular intake drogs slutsatsen att, för ett specular intake med en DC diameter på 37 mm, är den optimala intagslängden under 1 meter.

In dieser Arbeit werden verschiedene Prozesse zur Atomlagenabscheidung (ALD) von TiO2 und HfO2 experimentell untersucht. Die Untersuchungen schließen eine experimentelle Charakterisierung des Schichtwachstums sowie eine massenspektrometrische Analyse der Reaktionsprodukte ein. Im Detail wurden der ALD-Prozess mit Cp*Ti(OMe)3 und Ozon zur Abscheidung von TiO2 sowie der ALD-Prozess mit TEMAHf und Ozon zur Abscheidung von HfO2 untersucht. Der theoretische Teil der Arbeit beginnt mit einer Methode zur Bestimmung des absoluten Haftkoeffizienten. Anschließend werden numerische Modelle entwickelt, welche die Adsorption von Präkursormolekülen durch strukturierte Substrate beschreiben. Diese Modelle enthalten die Substratstruktur und den absoluten Haftkoeffizienten. Es wird eine statistische numerische Methode entwickelt, mit der der Gastransport in dem ALD-Reaktor statistisch beschrieben wird. Die statistischen Größen, welche die Gasdynamik im Reaktor beschreiben, werden mit der Discrete Simulation Monte Carlo (DSMC) Methode bestimmt. Mit dieser Methode und den Modellen der Adsorption kann der komplette ALD-Prozess simuliert werden. Die neu entwickelte Methode wird verwendet um die Effizienz verschiedener ALD-Reaktoren in Abhängigkeit des absoluten Haftkoeffizienten, der Substratstruktur sowie der Prozessbedingungen zu untersuchen. Die Geometrie des Reaktors wird variiert und mit der Referenzgeometrie verglichen.:Inhaltsverzeichnis................................................................................ i Tabellenverzeichnis.............................................................................. iii Abbildungsverzeichnis ......................................................................... v Abkürzungsverzeichnis ........................................................................ ix Formelverzeichnis ................................................................................ xi 1. Einführung ....................................................................................... 1 1.1. Motivation und Zielstellung ........................................................... 1 1.2. Grundlagen der Atomlagenabscheidung ....................................... 3 1.3. Materialien und Anwendungen ..................................................... 6 2. Experimentelle Grundlagen .............................................................. 9 2.1. ALD-Anlage ................................................................................... 9 2.2. Physikalische Probencharakterisierung ........................................ 11 2.2.1. Röntgenmethoden ..................................................................... 11 2.2.2. Elektronenstrahl-Methoden ....................................................... 12 2.2.3. Spektrometrische Methoden ...................................................... 13 2.3. Experimentelle in-situ Prozesscharakterisierung .......................... 14 3. Atomlagenabscheidung von TiO2 und HfO2 ..................................... 21 3.1. Abscheidung von Titandioxid ........................................................ 21 3.1.1. TDMAT als Titanpräkursor .......................................................... 21 3.1.2. Cp*Ti(OMe)3 als Titanpräkursor ................................................ 25 3.2. Abscheidung von Hafniumdioxid mit TEMAHf und Ozon ................. 30 3.3. Massenspektrometrie an ALD-Prozessen mit Ozon ...................... 32 3.3.1. Cp*Ti(OMe)3 mit Ozon .............................................................. 32 3.3.2. TMA mit Ozon ............................................................................ 36 3.3.3. TEMAHf mit Ozon ....................................................................... 37 3.3.4. Prozessüberwachung mit Massenspektrometrie ....................... 39 3.4. Zusammenfassung zur ALD von TiO2 und HfO2 ........................... 41 4. Modellierung der Adsorption ........................................................... 43 4.1. Adsorptionsverhalten planarer Substrate .................................... 43 4.2. Adsorptionsverhalten strukturierter Substrate ............................ 49 4.2.1. Numerische Simulationsmethode .............................................. 52 4.2.2. Gaskinetik in einem zylindrischen Graben ................................. 54 4.2.3. Effektive Haftkoeffizienten und Sättigungsdosen ..................... 55 4.2.4. Sättigungsprofile entlang der Grabenwand .............................. 59 4.3. Methode zur Bestimmung des absoluten Haftkoeffizienten von ALD-Präkursoren ........................................................................................ 61 4.3.1. Methode am Beispiel von TDMAT mit Ozon ................................ 66 4.3.2. Absoluter Haftkoeffizient von TEMAHf mit Ozon ......................... 74 4.3.3. Absoluter Haftkoeffizient von Cp*Ti(OMe)3 mit Ozon ................ 78 4.3.4. Temperaturabhängigkeit absoluter Haftkoeffizienten ............... 79 4.4. Zusammenfassung zur Modellierung der Adsorption .................... 81 5. Gekoppelte Prozesssimulation ........................................................ 83 5.1. Statistische Methode zur Simulation der ALD ............................... 83 5.1.1. Statistische Größen der Gasdynamik ......................................... 85 5.1.2. Algorithmus der gekoppelten ALD-Simulation ............................ 90 5.2. Anwendung der Methode zur Optimierung einer Gasdusche ........ 93 5.2.1. Geometrie und Randbedingungen ............................................. 93 5.2.2. Ergebnis der Reaktorsimulation ................................................. 96 5.2.3. Gekoppelte ALD-Simulation für planare Substrate ................... 102 5.2.4. Gekoppelte ALD-Simulation für strukturierte Substrate ........... 110 5.3. Einfluss der Randbedingungen auf die geometrische Effizienz ... 113 5.4. Vergleich zwischen Simulation und Experiment .......................... 114 6. Zusammenfassung und Ausblick .................................................... 117 Literaturverzeichnis ........................................................................... 121 Anhang .............................................................................................. 129 Parameter der modellierten effektiven Haftkoeffizienten ................... 129 Hafnium-Dotierung von Titandioxidschichten ..................................... 131 Eigene Veröffentlichungen ................................................................. 133 Lebenslauf ......................................................................................... 135 / This dissertation is divided into an experimental part and a theoretical part. The experimental part describes the atomic layer deposition (ALD) of TiO2 and HfO2. TDMAT and Cp*Ti(OMe)3 were used as titanium precursors, while TEMAHf was used as the hafnium precursor. Ozone was used as the oxygen source. The self limiting film growth and the temperature window of these ALD processes were investigated. The reaction by-products of the Cp*Ti(OMe)3/O3 process were identified by quadrupol mass spectrometry (QMS). The QMS analysis of the TEMAHf/O3 process revealed that water is formed during the metal precursor pulse. The theoretical part of this thesis describes the development of models and numerical methods to simulate the ALD as a whole. First of all, a model for the adsorption of precursor molecules by planar substrates was developed. This model was extended to describe the adsorption of precursor molecules inside a cylindrical hole with an aspect ratio of 20, 40 and 80. The adsorption of precursor molecules is dominated by the absolute sticking coefficient (SC), i.e., the reactivity of the precursor molecules. From the numerical model the saturation profiles along the wall of a cylindrical hole can be determined. From the comparison of the simulated profile with an experimentally determined thickness profile the SC can be determined. This method was used to determine the SC of the precursors examined in the experimental part. The SC of TEMAHf increases exponentially with the substrate temperature. A discrete particle method (DSMC) was used to derive a statistical description of the gas kinetics inside an ALD reactor. Combining the statistical description of the gas transport and the numerical models of the adsorption, it is possible to simulate the ALD for any combination of reactor, substrate and SC. It is possible to distinguish the contribution of the reactor geometry, the process parameters and the process chemistry (SC) to the process efficiency. Therefore, the ALD reactor geometry can be optimized independently of the process chemistry. This method was used to study a shower head ALD reactor. The reactor geometry, the composition of the gas at the inlet and the position of the inlet nozzles was varied in order to find more efficient ALD reactors. The efficiency of the reference geometry is limited by the inlet nozzles close to the exhaust and the decrease of the pressure on the substrate near the exhaust. The efficiency of ALD processes with different SCs was simulated for planar and structured substrates with a diameter of 300 mm and 450 mm.:Inhaltsverzeichnis................................................................................ i Tabellenverzeichnis.............................................................................. iii Abbildungsverzeichnis ......................................................................... v Abkürzungsverzeichnis ........................................................................ ix Formelverzeichnis ................................................................................ xi 1. Einführung ....................................................................................... 1 1.1. Motivation und Zielstellung ........................................................... 1 1.2. Grundlagen der Atomlagenabscheidung ....................................... 3 1.3. Materialien und Anwendungen ..................................................... 6 2. Experimentelle Grundlagen .............................................................. 9 2.1. ALD-Anlage ................................................................................... 9 2.2. Physikalische Probencharakterisierung ........................................ 11 2.2.1. Röntgenmethoden ..................................................................... 11 2.2.2. Elektronenstrahl-Methoden ....................................................... 12 2.2.3. Spektrometrische Methoden ...................................................... 13 2.3. Experimentelle in-situ Prozesscharakterisierung .......................... 14 3. Atomlagenabscheidung von TiO2 und HfO2 ..................................... 21 3.1. Abscheidung von Titandioxid ........................................................ 21 3.1.1. TDMAT als Titanpräkursor .......................................................... 21 3.1.2. Cp*Ti(OMe)3 als Titanpräkursor ................................................ 25 3.2. Abscheidung von Hafniumdioxid mit TEMAHf und Ozon ................. 30 3.3. Massenspektrometrie an ALD-Prozessen mit Ozon ...................... 32 3.3.1. Cp*Ti(OMe)3 mit Ozon .............................................................. 32 3.3.2. TMA mit Ozon ............................................................................ 36 3.3.3. TEMAHf mit Ozon ....................................................................... 37 3.3.4. Prozessüberwachung mit Massenspektrometrie ....................... 39 3.4. Zusammenfassung zur ALD von TiO2 und HfO2 ........................... 41 4. Modellierung der Adsorption ........................................................... 43 4.1. Adsorptionsverhalten planarer Substrate .................................... 43 4.2. Adsorptionsverhalten strukturierter Substrate ............................ 49 4.2.1. Numerische Simulationsmethode .............................................. 52 4.2.2. Gaskinetik in einem zylindrischen Graben ................................. 54 4.2.3. Effektive Haftkoeffizienten und Sättigungsdosen ..................... 55 4.2.4. Sättigungsprofile entlang der Grabenwand .............................. 59 4.3. Methode zur Bestimmung des absoluten Haftkoeffizienten von ALD-Präkursoren ........................................................................................ 61 4.3.1. Methode am Beispiel von TDMAT mit Ozon ................................ 66 4.3.2. Absoluter Haftkoeffizient von TEMAHf mit Ozon ......................... 74 4.3.3. Absoluter Haftkoeffizient von Cp*Ti(OMe)3 mit Ozon ................ 78 4.3.4. Temperaturabhängigkeit absoluter Haftkoeffizienten ............... 79 4.4. Zusammenfassung zur Modellierung der Adsorption .................... 81 5. Gekoppelte Prozesssimulation ........................................................ 83 5.1. Statistische Methode zur Simulation der ALD ............................... 83 5.1.1. Statistische Größen der Gasdynamik ......................................... 85 5.1.2. Algorithmus der gekoppelten ALD-Simulation ............................ 90 5.2. Anwendung der Methode zur Optimierung einer Gasdusche ........ 93 5.2.1. Geometrie und Randbedingungen ............................................. 93 5.2.2. Ergebnis der Reaktorsimulation ................................................. 96 5.2.3. Gekoppelte ALD-Simulation für planare Substrate ................... 102 5.2.4. Gekoppelte ALD-Simulation für strukturierte Substrate ........... 110 5.3. Einfluss der Randbedingungen auf die geometrische Effizienz ... 113 5.4. Vergleich zwischen Simulation und Experiment .......................... 114 6. Zusammenfassung und Ausblick .................................................... 117 Literaturverzeichnis ........................................................................... 121 Anhang .............................................................................................. 129 Parameter der modellierten effektiven Haftkoeffizienten ................... 129 Hafnium-Dotierung von Titandioxidschichten ..................................... 131 Eigene Veröffentlichungen ................................................................. 133 Lebenslauf ......................................................................................... 135

Ce manuscrit présente l'étude et l'analyse d'écoulements de gaz raréfiés, induits par la transpiration thermique. Le terme de transpiration thermique désigne le mouvement macroscopique d'un gaz raréfié engendré par l'effet du seul gradient de température. L'aspect principal de ce travail est centré autour de la mesure du débit stationnaire déclenché en soumettant un micro tube à un gradient de température appliqué le long de son axe. On a développé à cet effet un appareillage expérimental original ainsi qu'une méthodologie expérimentale innovatrice basée sur la dépendance du phénomène, analysé dans son ensemble, à l'égard du temps. Les résultats obtenus pour le débit stationnaire initial de transpiration thermique et pour les paramètres thermo-moléculaires caractérisant l'équilibre final de débit nul, ont été comparés aux résultats obtenus numériquement par la résolution de l'équation cinétique modèle de Shakhov et par la méthode de simulation directe de Monte-Carlo. / This thesis presents the study and analysis of rarefied gas flows induced by thermal transpiration. Thermal transpiration refers to the macroscopic movement of rarefied gas generated by a temperature gradient. The main aspect of this work is centered around the measurement of the mass flow rate engendered by subjecting a micro-tube to a temperature gradient along its axis. In this respect, an original experimental apparatus and an original time-dependent experimental methodology was developed. The experimental results for the initial stationary thermal transpiration mass flow rate and for the final zero- flow thermal molecular parameters were compared with the results obtained from the numerical solution of the Shakhov model kinetic equation and the direct simulation Monte Carlo method.

Les méthodes Direct Simulation Monte Carlo (DSMC) sont utilisées par Ariane group pour calculer les torseurs d'efforts aérodynamiques et les flux thermiques sur les engins spatiaux pour des écoulements hypersoniques en milieu raréfié.Afin de pouvoir caractériser la dislocation des étages de lanceurs et donc l'empreinte de retombée de débris, une modélisation précise des mécanismes générateurs de flux thermiques est nécessaire. Les réactions chimiques étant dimensionnantes pour le calcul du flux thermique, l'objectif de cette thèse est de développer l'outil de calcul avec la méthode DSMC nommé IEMC de manière à pouvoir prendre en compte les écoulements réactifs.Deux modèles de chimie sont mis en place pour pouvoir prendre en compte la totalité des réactions. Après leur vérifications sur des cas élémentaires, ils sont appliqués et validés sur des cas tests de rentrée pour différentes atmosphères. Les différents modèles considérés sont testés afin d'évaluer leur influence. Les modèles de chimie dépendent de nouveaux paramètres d'entrée, dont les valeurs numériques sont incertaines. Une étude de quantification de leur incertitude est menée et a permis de vérifier que les grandeurs de sorties de la simulation avec un écoulement réactif, notamment le flux thermique, n'est que peu impacté par ces paramètres incertains. / Direct Simulation Monte Carlo (DSMC) methods are used in Ariane group to compute aerodynamic forces and moments and heat fluxes on space objects for hypersonic flows in rarefied regimes.To caracterise the dislocation of the stages and the debris footprints, a precise modelisation of the mechanism that contribute to the heat flux is necessary. The contribution of the chemical reactions is important for the determination of the heat flux. The purpose of this thesis is to develop the in house IEMC tool using the DSMC method so that it can compute reactive flows.The different steps of the developments are presented in this work. The first step is the presentation, implementation and verification of two different chemistry models. They are validated for simulations on real test cases. Different models are tested in order to evaluate their effect. Chemical models implemented in the code depend on new input parameters, whose numerical data are uncertain. Using a uncertainty quantification study, it is shown that the output data of the reactive simulation, especially the heat flux, is weakly impacted by the tested uncertain parameters.

La thèse est consacrée à la modélisation et à l'analyse par voie numérique de l'écoulement dans une pompe à vide turbomoléculaire hybride, combinant une succession d'étages de type rotor et stator et un Holweck. Une approche de type Test Particle Monte Carlo 3D a été développée pour des configurations de pompes industrielles (géométries complexes d'aubes, gestion des étages rotor et stator) dans un souci d'optimisation des coûts de simulation. L'outil numérique développé a été validé pour des configurations académiques et industrielles, en s'appuyant notamment sur des résultats expérimentaux obtenus grâce au banc d'essai de l'entreprise aVP. L'apport de l'approche TPMC3D par rapport aux méthodes de design disponibles en début de thèse a été clairement démontré pour le régime moléculaire libre. Quelques préconisations de design ont également pu être formulées en utilisant le code développé. Le potentiel d'une approche de type Direct Simulation Monte Carlo, prenant en compte les interactions entre molécules du gaz, a également été établi en 2D pour le régime de transition. / The thesis is devoted to the modeling and the numerical analysis of the flow in a turbomolecular vacuum pump of hybrid type, that is combining a succession of rotor and stator stages with an Holweck. A 3D Test Particle Monte Carlo approach has been developed for simulating industrial pump configurations (complex blade geometries, management of rotor and stator stages), with attention paid to the optimization of the computational cost. The numerical tool developed in the thesis has been validated for academic and industrial test cases, relying in particular on reference experimental results obtained on the test rig of the aVP company. The prediction improvement brought by the TPMC 3D approach with respect to the design tools available at the start of the thesis has been clearly demonstrated for the free molecular flow regime. Some design recommendations have also been formulated using the developed solver. The potential of a Direct Simulation Monte Carlo approach, taking into account the interactions between gas molecules, has also been established in 2D for the transition regime.

Cette thèse présente une étude numérique et expérimentale d’écoulements gazeux raréfiés confinés, induits par gradients thermiques. L’écoulement d’un gaz raréfié peut en effet être généré en appliquant uniquement un gradient tangentiel de température le long d'une paroi. Ainsi, sans gradient initial de pression, le gaz peut se déplacer de la région froide vers la région chaude. Ce phénomène, appelé transpiration thermique, est à la base du fonctionnement des pompes dites de Knudsen, capables de générer un pompage du gaz sans utiliser de pièces mécaniques mobiles. L’apport principal de ce travail est relatif à l’investigation numérique de l’écoulement de transpiration thermique dans trois nouvelles configurations de pompe Knudsen. Dans ce but, une méthode numérique de simulation d’écoulements dans le régime de glissement a été développée ; elle implémente des conditions aux limites de saut de vitesse et de température spécifiques dans un code CFD commercial. Parallèlement, un code DSMC a été mis en œuvre pour étudier des écoulements plus fortement raréfiés dans les géométries les plus complexes. Des écoulements de transpiration thermique générés dans des canaux courbés, dans des canaux convergents/divergents ou entre deux surfaces spécialement micro-texturées ont ainsi été étudiés. D’autre part, l’analyse expérimentale d’un écoulement de transpiration thermique dans un microtube de section circulaire a été réalisée sur un nouveau banc d’essais conçu pour être adaptable à diverses géométries de canaux ou de pompes Knudsen. / This thesis presents a numerical and experimental analysis of internal rarefied gas flows induced by temperature fields. In rarefied gases, a flow can be generated by solely applying a tangential temperature gradient along a wall: without any initial pressure gradient, the gas macroscopically moves from the cold toward the hot region. This phenomenon is the so-called thermal creep or thermal transpiration effect. It is the main operating principle of the Knudsen pump, which can generate gas pumping without the need of any moving parts. The main aspect of this work is centered on numerical investigations of thermal transpiration flows in three new possible configurations of Knudsen pumps. For that goal, a numerical model for slip flows has been developed in which the appropriate slip boundary conditions are implemented in a commercial CFD code and a DSMC code has been adapted for studying transition flows in complex geometries. The pumping effect of curved-channel Knudsen pumps, the thermal transpiration flows through tapered channels and between two ratchets surfaces at different uniform temperatures have been investigated. In addition, an experimental study of thermal transpiration flow through a single micro-tube has been carried out on a new experimental set-up designed to be adaptable for testing thermally driven flows through various kinds of microchannels or generated by autonomous Knudsen compressors