Transport d'un scalaire passif dans une turbulence magnétohydrodynamique

Notre étude est consacrée à la simulation numérique d'une turbulence homogène évoluant sans gradient de vitesse moyenne soumise à l'action d'un champ magnétique statique. Cette simulation montre que la force de Laplace a deux effets,un effet dissipatif et un effet structural.Dans la deuxième partie,nous avons simuler numériquement une turbulence hydrodynamique cisaillée.En présence d'un cisaillement fort,le flux turbulent est pratiquement concentré dans la direction de l'écoulement moyen.Lorsque la turbulence est sujette à un champ magnétique extérieur,deux régimes sont distingués

K-epsilon model for rotating homogeneous decaying turbulence

In the present work, we propose a modification to the standard K − model for sim2ulating homogeneous decaying turbulence subjected to uniform rotation . In this modification, the dissipation rate equation is formulated in terms of the rotation rate Ω, the integral length scales along the axis of rotation L‖ and its isotropic value L0 . The comparison of our results with the corresponding DNS simulations proves that the new model reproduces in excellent way the decay rate of the turbulent kinetic energy.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Thermal conduction effects on the accretion-ejection mechanism. Outflow process investigation

Astrophysical jets emanating from different systems are one of the most spectacular and enigmatic phenomena pervading the Universe. These jets are typically bipolar and span hundreds of thousands of light years, some even longer than the diameter of our Milky Way. The study of the disc-jet systems is motivated by the observed correlation between ejection and accretion signatures and is still under debate. It was shown in our previous work the crucial role of thermal conduction in the dynamics of a thin viscous resistive accretion disc orbiting a central object and was provided an unprecedented wealth of discussion that has advanced our understanding of the inflow process. In this work, we expand our exploration by addressing the most outstanding basic questions concerning the launching, acceleration, and collimation processes of the jet in presence of thermal conduction. We also tackle in depth-analysis the effects of this physical ingredient on the time evolution of temperature and on mass fluxes such as inflow and outflow rates. We performed a series of 2.5-dimensional non-relativistic time-dependent numerical calculations of a disc-jet system using the PLUTO code. Our results revealed compelling evidence that thermal conduction contributes to launching a faster and more collimated jet. The mass extracted from the disc via the outflow channel is also affected by the presence of thermal conduction in the sense that the ejection efficiency is significantly improved