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Atomization modeling of liquid jets using an Eulerian-Eulerian model and a surface density approach / Modélisation de l'atomisation des jets liquides avec un modèle Eulérien-Eulérien et une approche de densité de surfaceMandumpala devassy, Bejoy 25 January 2013 (has links)
Dans les moteurs à combustion interne, l'injection de carburant est une phase essentielle pour la préparation du mélange et la combustion. En effet, la structure du jet liquide joue un rôle essentiel pour la qualité du mélange du combustible avec le gaz. Le présent travail porte sur les phénomènes d'atomisation de jet liquides dans les conditions opératoires des moteurs diesel. Dans ces conditions, la morphologie du jet liquide comprend une phase liquide séparée (c'est à dire un noyau liquide) et une phase liquide dispersée (c'est à dire un spray). Ce manuscrit décrit les étapes de développement d'un nouveau modèle d'atomisation, pour un jet liquide à grande vitesse, basée sur une approche eulérienne diphasique. Le phénomène d'atomisation est modélisée par des équations définissant une densité de surface pour le noyau liquide en plus de celle des gouttelettes du spray. Ce nouveau modèle a été couplé avec un système d'équations diphasique et turbulent de type Baer-Nunziato. Le processus de rupture des ligaments et son éclatement subséquent en gouttelettes sont modélisés en utilisant des connaissances rassemblées à partir des expériences disponibles et des simulations numériques précises. Dans la région dense du jet de liquide, l'atomisation primaire est modélisée comme un processus de dispersion en raison de l'étirement turbulent de l'interface, à partir du côté du liquide en plus du côté du gaz. Différents cas tests académiques ont été effectués afin de vérifier la mise en œuvre numérique du modèle dans le code IFP-C3D. Enfin, le modèle est validé avec les résultats DNS récemment publiés dans des conditions typiques de moteurs Diesel à injection directe. / In internal combustion engines, the liquid fuel injection is an essential step for the air/fuel mixture preparation and the combustion process. Indeed, the structure of the liquid jet coming out from the injector plays a key role in the proper mixing of the fuel with the gas in the combustion chamber. The present work focuses on the liquid jet atomization phenomena under Diesel engine conditions. Under these conditions, liquid jet morphology includes a separate liquid phase (i.e. a liquid core) and a dispersed liquid phase (i.e. a spray). This manuscript describes the development stages of a new atomization model, for a high speed liquid jet, based on an eulerian two-phase approach. The atomization phenomenon is modeled by defining different surface density equations, for the liquid core and the spray droplets. This new model has been coupled with a turbulent two-phase system of equations of Baer-Nunziato type. The process of ligament breakup and its subsequent breakup into droplets are handled with respect to available experiments and high fidelity numerical simulations. In the dense region of the liquid jet, the atomization is modeled as a dispersion process due to the turbulent stretching of the interface, from the side of liquid in addition to the gas side. Different academic test cases have been performed in order to verify the numerical implementation of the model in the IFP-C3D software. Finally, the model is validated with the recently published DNS results under typical conditions of direct injection Diesel engines.
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High order numerical methods for a unified theory of fluid and solid mechanicsChiocchetti, 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.
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