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1	Étude de l'ébullition sur plaque plane en microgravité, application aux réservoirs cryogéniques des fusées Ariane V / Study of nucleate boiling in microgravity conditions, aplicated to the ArineV cryogenics tanks Kannengieser, Olivier 18 December 2009 (has links) Ce rapport de thèse porte sur une étude expérimentale et théorique de l'ébullition en microgravité. Les expériences furent réalisées en condition de gravité terrestre, en vol parabolique et en fusée-sonde. Les expériences en vol parabolique ont montré l'influence de divers paramètres sur le transfert thermique et ont mis en évidence les mécanismes contrôlant le transfert thermique. De l'écriture des équations gouvernant ces mécanismes et de l'identification des échelles caractéristiques, une corrélation permettant d'estimer le transfert de chaleur lors de l'ébullition en microgravité pour une large gamme de fluide est bâtie. L'expérience en fusée-sonde a permis d'étudier l'influence des gaz incondensables et notamment de la convection Marangoni sur le comportement de l'ébullition et sur le transfert thermique. / Between the different propulsion phases, the Ariane V rocket passes through microgravity periods and solar radiation can induce boiling in its cryogenics tanks. Experiments were performed during 6 parabolic flights and in a sounding rocket to study pool boiling in microgravity. In the parabolic flight experiments, the influence of pressure, subcooling and surface roughness was studied. It is showed that subcooling has a weak effect on microgravity boiling heat transfer, and that roughness is an important factor also in microgravity. Detailed results on the behavior of bubbles and on the superheated liquid layer show that the heat transfer mechanisms can be divided in two groups : the primary mechanisms which directly take energy from the wall and the secondary mechanisms which transport the energy stored in the fluid by the primary mechanisms, from the vicinity of the wall to the bulk liquid. The secondary mechanisms appear not to limit primary mechanism heat transfer which explains the weak influence of gravity on heat transfer. From the study of equations governing primary mechanisms and the definition of new scales, a correlation is built to predict heat transfer in microgravity for a wide variety of fluids. In the sounding rocket experiment, the influence of non-condensable gases was studied. The existence of two regimes of boiling heat transfer with non-condensable gas is established. The temperature in the primary bubble is directly measured and the influences of both Marangoni convection and non-condensable gas on both heat transfer and bubble growth are also considered. Ariane V Ebulition Microgravité Corrélation Refrigérant Cryogenique Mécanisme de transfert de chaleur Analyse dimensionnelle Gaz dissoud Vol parabolique Fusée sonde Mécanique des fluides Transfert de chaleur Boiling Microgravity Correlation Refrigerant Cryogenics Heat transfer mechanisms Dimensionless analysis Disolved gas Parabolic flight Sounding rocket Fluid mechanic Heat transfer
2	High order numerical methods for a unified theory of fluid and solid mechanics Chiocchetti, Simone 10 June 2022 (has links) This dissertation is a contribution to the development of a unified model of continuum mechanics, describing both fluids and elastic solids as a general continua, with a simple material parameter choice being the distinction between inviscid or viscous fluid, or elastic solids or visco-elasto-plastic media. Additional physical effects such as surface tension, rate-dependent material failure and fatigue can be, and have been, included in the same formalism. The model extends a hyperelastic formulation of solid mechanics in Eulerian coordinates to fluid flows by means of stiff algebraic relaxation source terms. The governing equations are then solved by means of high order ADER Discontinuous Galerkin and Finite Volume schemes on fixed Cartesian meshes and on moving unstructured polygonal meshes with adaptive connectivity, the latter constructed and moved by means of a in- house Fortran library for the generation of high quality Delaunay and Voronoi meshes. Further, the thesis introduces a new family of exponential-type and semi- analytical time-integration methods for the stiff source terms governing friction and pressure relaxation in Baer-Nunziato compressible multiphase flows, as well as for relaxation in the unified model of continuum mechanics, associated with viscosity and plasticity, and heat conduction effects. Theoretical consideration about the model are also given, from the solution of weak hyperbolicity issues affecting some special cases of the governing equations, to the computation of accurate eigenvalue estimates, to the discussion of the geometrical structure of the equations and involution constraints of curl type, then enforced both via a GLM curl cleaning method, and by means of special involution-preserving discrete differential operators, implemented in a semi-implicit framework. Concerning applications to real-world problems, this thesis includes simulation ranging from low-Mach viscous two-phase flow, to shockwaves in compressible viscous flow on unstructured moving grids, to diffuse interface crack formation in solids. High order ADER Discontinuous Galerkin DG Finite Volume FV Finite Element FE FEM DGFEM CFD Voronoi Delaunay Unstructured meshe Fortran Fluid mechanic Solid Mechanic Continuum Mechanic Baer Nunziato Surface tension Multiphase flow Compressible flow Navier Stoke Semi-implicit GLM cleaning Partial differential equation Numerical method Stiff source Finite rate stiff relaxation Hyperbolic equation Metodi d'alto ordine ADER Discontinous Galerkin Volumi Finiti Elementi Finiti Meccanica dei fluidi Meccanica dei solidi Meccanica dei continui Fluidi multifase Fluidi comprimibili Metodi semi-impliciti Equazioni alle derivate parziali Metodi numerici Equazioni iperboliche Griglie non strutturate

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Étude de l'ébullition sur plaque plane en microgravité, application aux réservoirs cryogéniques des fusées Ariane V / Study of nucleate boiling in microgravity conditions, aplicated to the ArineV cryogenics tanks

High order numerical methods for a unified theory of fluid and solid mechanics