Simulation 2D et 3D des écoulements cavitants : développement d'un algorithme original dans Code_Saturne et étude de l'influence de la modélisation de la turbulence.

Abstract : Cavitation is one of the most demanding physical phenomena influencing the performance of hydraulic machines. It is therefore important to predict correctly its inception and development, in order to quantify the performance drop it induces, and also to characterize the resulting flow instabilities. The aim of this work is to develop an unsteady 3D algorithm for the numerical simulation of cavitation in an industrial CFD solver « Code_saturne ». It is based on a fractional step method and preserves the minimum/maximum principle of the void fraction. An implicit solver, based on a transport equation of the void fraction coupled with the Navier-Stokes equations is proposed. A specific numerical treatment of the cavitation source terms provides physical values of the void fraction (between 0 and 1) without including any artificial numerical limitation. The influence of RANS turbulence models on the simulation of cavitation on 2D geometries (Venturi and Hydrofoil) is then studied. It confirms the capability of the two-equation eddy viscosity models, k-epsilon and k-omega-SST, with the modification proposed by Reboud et al. (1998) to reproduce the main features of the unsteady sheet cavity behavior. The second order model RSM-SSG, based on the Reynolds stress transport, appears able to reproduce the highly unsteady flow behavior without including any arbitrary modification. The three-dimensional effects involved in the instability mechanisms are also analyzed. This work allows us to achieve a numerical tool, validated on complex configurations of cavitating flows, to improve the understanding of the physical mechanisms that control the three-dimensional unsteady effects involved in the mechanisms of instability.
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Rezki Chebli. Simulation 2D et 3D des écoulements cavitants : développement d'un algorithme original dans Code_Saturne et étude de l'influence de la modélisation de la turbulence.. Génie mécanique [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2014. Français. ⟨NNT : 2014ENAM0040⟩. ⟨tel-01204605⟩

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