Ce travail est l'expression d'une volonté de chercheurs, de la Carabe d'améliorer les connaissances scientifiques méso- et micro-météorologiques appliquées aux milieux insulaires sous influence des alizés et de développer la recherche dans ces domaines.On sait que le phénomène météorologique le plus remarquable impactant les îles de la Caraïbe reste le cyclone tropical. Mais d'autres phénomènes, a des échelles inferieures, telles que les pluies intenses, les houles, la dégradation de la qualité de l'air ont une importance aigüe en termes de risques naturels ou de risques sur la sante. Ces exemples attestent la nécessité d'utiliser des méthodes de descente d'échelle pour exploiter l'information météorologique et/ou climatique de grande échelle et dériver des scenarios locaux et régionaux appliques aux territoires insulaires. Ce défi est important car l'attente d'analyses scientifiques pertinentes dans ces domaines est grande.Les travaux présentés dans ce mémoire ont pour principaux objectifs la simulation numérique puis l'analyse des mécanismes méso- et micro-échelles qui induisent des circulations locales diurnes et nocturnes sur l'archipel de la Guadeloupe à l'aide de codes numériques météorologiques éprouves car largement utilises en recherche et en prévision opérationnelle.Ils constituent donc la première étude de modélisation numérique à haute résolution en basse atmosphère, par descente d'échelle dynamique, pour des intervalles d'espace compris entre 1 km et 111 m sur cet archipel.Le modelé atmosphérique Weather Research and Forecasting ARW V3.4 (WRF ARW), non-hydrostatique, a été utilise pour l'ensemble des simulations pour modéliser la troposphère depuis l'échelle globale à l'échelle de la turbulence.Trois situations météorologiques classiques réelles d'une durée de 48 heures, correspondant à 80 % des situations météorologiques observées dans la zone, alizes soutenus (AS), alizes moyens (AM), alizes faibles (AF) ont été examinées. Ces situations sont caractérisées par les valeurs du nombre de Froude local suivantes : 0,82 (AS), 0,41 (AM) et 0,21 (AF). Six domaines de modélisation ont été sélectionnés pour effectuer les descentes d'échelle dynamiques : D01 (maille de 27 km), D02 (maille de 9 km), D03 (maille de 3 km), D04 (maille de 1 km), D05 (maille de 333 m) et D06 (maille de 111 m) avec soixante-dix niveaux verticaux. Les quatre premiers domaines (D01 à D04) couvrent l'archipel de la Guadeloupe et sont utilisés en mode méso-échelle à l'aide d'un schéma d'ensemble de couche limite planétaire YSU. Les domaines D05 (couvrant l'île de la Basse-Terre et le centre de l'archipel) et D06 (couvrant la zone littorale et rurale du Petit Cul-de-Sac Marin et la zone urbaine de l'agglomération pointoise) sont utilisés en mode Large Eddy Simulation avec une fermeture de la turbulence 1,5 TKE 3D. Le modèle WRF a été forcé toutes les six heures par l'assimilation des champs d'analyses globales du modèle NCEP FNL (1° de résolution). Les simulations effectuées ont permis d'obtenir des champs de variables météorologiques 10-minutes à très hautes résolutions spatiales.Les résultats des simulations méso- et micro-échelles ont été confrontés aux valeurs expérimentales obtenues à l'aide de capteurs places sur des mâts météorologiques (campagne Atmo-Mangrov et réseau de mesure Météo-France). Il s'agissait d'optimiser l'utilisation des couplages de codes numériques tout en conservant la possibilité de les confronter aux observations expérimentales.Les résultats des simulations numériques micro-échelles, des différents cas (AS, AM, AF) sont utilisées pour forcer (c'est-à-dire définir les conditions limites) un modèle lagrangien de dispersion de particules : FLEXPART. Le système couple FLEXPART-WRF a été employé dans le domaine D06 pour étudier la dispersion du panache d'oxydes d'azote émis par la principale usine de production d'électricité de l'île. / The present work expresses the will of Caribbean researchers to improve the meso- and micro-meteorological scientific knowledge of the trade winds influenced island areas, and to develop research in these domains.It is well known that tropical hurricanes remain the most remarkable meteorological phenomena that affect the Caribbean islands. But some other phenomena, of smaller scale, such as intense rainfall events, swells, or air quality degradation, are of extreme importance for natural or health hazards. These examples show the need to use downscaling methods to exploit large scale meteorological or climatic information, and to obtain local and regional scenarios for the island areas. This is an important challenge, as sound scientific studies in these matters are eagerly expected. The aim of the research works exposed in the present dissertation is numerical simulation and analysis of the meso- and microscale mechanisms that induce diurnal and nocturnal local circulations in the Guadeloupe archipelago, using numerical meteorological models that are widely used in research and in operational forecasting.These works represent the first high-resolution (1 km to 111 m) numerical study of the lower atmosphere over the Guadeloupe archipelago. The Weather Research and Forecasting ARW 3.4 (WRF-ARW) model is used to simulate the troposphere from global scale to turbulence scale. Real cases of three typical weather types (80% of cases during a year) are examined during 48 hours : strong trade winds (STW), medium trade winds (MTW) and weak trade winds (WTW). These weather types are characterized by values of the local Froude number : 0.82 (STW), 0.41 (MTW) and 0.21 (WTW). Six domains have been selected for the dynamical downscaling : D01 (grid spacing of 27 km), D02 (grid spacing of 9 km), D03 (grid spacing of 3 km), D04 (grid spacing of 1 km), D05 (grid spacing of 333 m) and D06 (grid spacing of 111 m), including 70 vertical levels. The first four domains (D01 to D04) cover the Guadeloupe archipelago and are used in the meso-scale simulations with the planetary boundary layer scheme YSU (ensemble mean). Domain D05 (covering the Basse-Terre island and the middle of the archipelago) and domain D06 (covering the coastal and rural area of Le Petit Cul-de-Sac Marin and the urban area of Pointe-à-Pitre), are employed in the micro-scale simulation (LES) with the 3D TKE 1.5 order closure scheme. WRF has been 6 hourly reinitialized with the NCEP FNL global analyses (resolution of 1°). These simulations permitted to obtain 10-minutes meteorological variable fields with a very high resolution (111 m).Meso-scale and micro-scale model results have been evaluated with observational data from meteorological stations (field campaign Atmo-Mangrov, French Met Office).Once validated, the micro-scale model outputs have been used for the assimilation of the lagrangian particle dispersion model : FLEXPART. The coupling FLEXPART-WRF has been employed in domain D06, in order to analyze the dispersion of the nitrogen oxide plume emitted by the main power plant of the archipelago.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第20727号 / エネ博第355号 / 新制||エネ||70(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 岸本 泰明, 教授 中村 祐司, 教授 田中 仁 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

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Significant effort has been placed on the development of surfaces which reduce the amount of drag experienced by a fluid as it passes over the surface. Alterations to the fluid itself, as well as the chemical and physical composition of the surface have been investigated with varying success. Investigations into turbulent drag reduction have been mostly limited to those involving bubbles and riblets. Superhydrophobic surfaces, which combine hydrophobic surface chemistry with a regular array of microfeatures, have been shown to provide significant drag reduction in the laminar regime, with the possibility of extending these results into turbulent flows. Direct numerical simulations are used to investigate the drag reducing performance of superhydrophobic surfaces in turbulent channel flow. Slip velocities, wall shear stresses, and Reynolds stresses are considered for a variety of superhydrophobic surface microfeature geometry configurations at friction Reynolds numbers of Re = 180, Re = 395, and Re = 590. This work provides evidence that superhydrophobic surfaces are capable of reducing drag in turbulent flow situations by manipulating the laminar sublayer and turbulent energy cascade. For the largest micro-feature spacing of 90 microns an average slip velocity over 80% of the bulk velocity is obtained, and the wall shear stress reduction is found to be greater than 50%. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress, but is offset by a slip velocity that increases with increasing micro-feature spacing.

Plasmonic effects in nanosized particles enhance the interaction between light and matter due to the localized surface plasmon resonance, with potential applications such as all-optical transistors and optical computers. Commonly, the dynamics of nanoparticles’ optical properties are assessed via pump-probe spectroscopy, where a plasmonic structure is exited by an initial laser, the pump. Thereafter a second, less intense laser, a probe, interacts with the now excited structure at a time delay. Through measurements of the probelight transmitted by the matter, the optical dynamics of the structure are monitored. Similar methodologies can potentially be used for other applications as well, such as all-optical switching. This study focuses on an implementation of a numerical finite element method model simulating a pump-probe experiment to predict the effects of different geometries and evaluate experimental data. The simulations are split into three parts. Initially, periodically spaced nanoparticles are excited by the pump laser. Then the model estimates the internal thermal dynamics of the excited nanoparticles and in turn, determines the change in complex permittivity. Lastly, the probe-matter interaction is modeled. To evaluate the model, a comparison with another model was performed. Furthermore, simulations of periodically spaced gold dimer nanoparticles in air were done to investigate how dimers affect transmitted light. For a probe light polarization rotated 45◦ against the axis parallel to the dimer, a change in rotation of 6◦ over 35 fs was induced by the pump, indicating a potential switching mechanism.

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This thesis evaluates two variants of Volumeof fluid method, namely Piecewise Linear Interface Construction (PLIC) and Multidimensional Tangent of Hyperbola for Interface Capturing (MTHINC) used in two-fluid simulations for interface tracking.Simulations of a single rising bubble in different conditions are performed aimed to assess the accuracy of the methods, and to check their convergence with grid size. The results show that both methods demonstrate convergence with mesh refinement, while PLIC captures the transient part of rising process of bubble more accurately than MTHINC in 2D case. / Denna avhandling utvärderar två varianter av metoden Volume of fluid för flerfas strömningar, nämligen Piecewise Linear Interface Construction (PLIC) och Multidimensional Tangent of Hyperbola for Interface Capturing (MTHINC) som används i tvåvätskesimuleringar för gränssnittsspårning.Simuleringar av en enda stigande bubbla under olika förhållanden utförs för att bedöma metodernas noggrannhet och för att kontrollera deras konvergens med gridsstorlek. Resultaten visar att båda metoderna visar konvergens med grid förfining, medan PLIC fångar den övergående delen av stigande bubbelprocess mer exakt än MTHINC i 2D-fall.

To access and operate in space, a wide range of propulsion systems has been developed, from high-thrust chemical propulsion to low-thrust electrical propulsion, and new kind of systems are considered, such as solar sails and nuclear propulsion. Recently, interest in hybrid rocket engines has been renewed due to their attractive features (safe, cheap, flexible) and they are now investigated and developed by research laboratories such as ONERA.This master’s thesis work is in line with their development at ONERA and aims at finding a methodology to study numerically the liquid oxidizer injection using a Lagrangian solver for the liquid phase. For this reason, it first introduces a model for liquid atomiser developed for aeronautical applications, the FIMUR model, and then focuses on its application to a hybrid rocket engine configuration.The FIMUR model and the Sparte solver have proven to work fine with high mass flow rates on coarse grids. The rocket engine simulations have pointed out the need of an initialisation of the flow field. The methodology study has proven that starting with a reduced liquid mass flow rate is preferable to a simulation with a reduced relaxation between the coupled solvers. The former could not be brought to conclusion due to lack of time but gives an encouraging path to further investigate.