Using numerical methods, we systematically study in the framework of ideal
MHD the effect of magnetic fields on heat transfer within a turbulent gas. We
measure the rates of passive scalar diffusion within magnetized fluids and make
the comparisons a) between MHD and hydro simulations, b) between different MHD
runs with different values of the external magnetic field (up to the energy
equipartition value), c) between thermal conductivities parallel and
perpendicular to magnetic field. We do not find apparent suppression of
diffusion rates by the presence of magnetic fields, which implies that magnetic
fields do not suppress heat diffusion by turbulent motions.Comment: 4 pages; 2 figures; submitted to Ap
A subgrid-scale estimation procedure investigated previously for incompressible turbulence is extended to compressible flows. In the procedure the primary modeled quantities are the unfiltered velocity and temperature fields appearing in the expressions for the subgrid-scale stress tensor and heat flux. Estimates of the unfiltered fields are obtained from the known resolved fields in two steps. In the deconvolution step an approximate inversion of the filtering operation is performed. Subsequently, the nonlinear terms in the momentum and energy equations for the deconvolved quantities are used to generate a range of subgrid scales on a mesh two times smaller than the mesh employed for a discretization of the resolved quantities. Subgrid-scale stress and heat flux are computed directly from the definitions using estimated fields consisting of the deconvolved part and the nonlinear correction. The procedure has been applied and validated in a priori analyses and actual large eddy simulations of spatially decaying turbulence and shock/turbulence interaction exhibiting a very good agreement with filtered direct numerical simulation results. In all cases comparisons with the results provided by the standard implementation of the dynamic model are also made.
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