Les situations où deux fluides non miscibles sont présents dans un matériau granulaire déformable sont largement rencontrées dans la nature et dans de nombreux domaines de l'ingénierie et de la science. Comprendre l'évolution de tels systèmes multiphases nécessite la connaissance de toutes les phases, leur distribution et interactions. Un modèle micro-hydromécanique couplé est présenté dans cette thèse sur la base de travaux précédents, visant à simuler le drainage quasi-statique de matériaux granulaires déformables. Il combine une approche de type réseau de pores et la méthode des éléments discrets (DEM) pour les fluides et les grains respectivement. Un critère local de mouvement d'interfaces fluides est établi, afin d'approximer au mieux le rôle de la géométrie porale sur les phénomènes capillaires et notamment les forces exercées sur les grains solides à l'intérieur de chaque pore. Une attention particulière est dédiée aux événements de piégeage du fluide drainé et à l'invasion préférentielle le long des bords du domaines. Le modèle est valide par la comparaison avec des résultats expérimentaux (courbes de rétention d'eau). Nous appliquons le modèle pour étudier deux questions: (1) les effets de taille finie et à la question du volume élémentaire représentatif (REV); (2) le paramètre de contrainte effective de Bishop et la relation entre contrainte effective macroscopique contrainte de contact micromécanique. Finalement, une extension du modèle au régime pendulaire est présentée et des premiers résultats sont présentés et discutés. / The situation of two immiscible fluids through a deformable granular material is widely encountered in nature and in many areas of engineering and science. To understand the physical evolution of the multiphase system is of great importance for the applications. It requires the knowledge of all component phases, their distribution and interactions. A pore-scale coupled hydromechanical model is presented in this thesis based on previous work, aiming at simulating the quasi-static drainage of a deformable granular materials. The model combines a pore network approach and the discrete element method (DEM) for the fluids and grains, respectively. A local criterion for determining the local movements of the fluids interfaces established to approximate the role of the local pore geometry on capillarity and namely on the forces exerted on the solid grains inside each pore. Special attentions have been paid to the entrapment events of the receding fluid and to the preferential invasion along the boundaries. The model is validated through comparisons with experimental results (water retention curves). We apply the model for examining two issues: (1) finite size effects and the concept of representative elementary volume (REV); (2) Bishop's effective stress parameter and to the relationship between macro-scale effective stress and micro-scale contact stress. Finally, an extension to the pendular regimes is proposed and first results are presented and analyzed.

A compact air separator demonstrator based on centrifugally enhanced distillation has been studied. The full size device is meant to be used on board of a Two Stage To Orbit vehicle launcher. The air separation system must be able to extract oxygen in highly concentrated liquid form (LEA, Liquid Enriched Air) from atmospheric air. The LEA is stored before being used in a subsequent rocket propulsion phase by the second stage of the launcher. Two reference vehicles are defined, one with a subsonic first stage and one with a supersonic first stage. In both cases, oxygen collection is performed during a cruise phase (M 0.7 and M 2.5 respectively). The aim of the project is to demonstrate the feasibility of the air separation system, investigate the separation cycle design, and assess that the separator design selected is suitable for the reference vehicles.<p><p>The project is described from original base ideas to design, construction, extended testing and analysis of experimental results. Preliminary computations for a realistic layout have been performed and the motivations for the choices made during the process are explained. Test rig design, separator design and technical discussion are provided for a subscale pilot unit. Mass transport parameters and flooding limits have been estimated and experimentally measured. Performance has been assessed and shown to be sufficient for the reference Two Stage To Orbit vehicles. The technology developed is found suitable without further optimization, although some volume and mass reduction would be desirable for the supersonic first stage concept. There are many ways of optimisation that can be further investigated. The aim of this program, however, is not to fully optimize the device, but to demonstrate that a device based on a simple, robust, low-risk design is already suitable for the launch vehicles. On top of that analysis, directions for improvements are suggested and their potentials estimated. A complete assessment of those improvements requires further maturation of the technological concept through further testing and practical implementations.<p><p>Directions for future work, general conclusions and a vehicle development roadmap have also been provided.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished