Diffusion and dispersion of passive tracers: Navier-Stokes versus MHD turbulence

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A comparison of turbulent diffusion and pair-dispersion in homogeneous, macroscopically isotropic Navier-Stokes (NS) and nonhelical magnetohydrodynamic (MHD) turbulence based on high-resolution direct numerical simulations is presented. Significant differences between MHD and NS systems are observed in the pair-dispersion properties, in particular a strong reduction of the separation velocity in MHD turbulence as compared to the NS case. It is shown that in MHD turbulence the average pair-dispersion is slowed down for $τ_\mathrm{d}\lesssim t\lesssim 10 τ_\mathrm{d}$, $τ_\mathrm{d}$ being the Kolmogorov time, due to the alignment of the relative Lagrangian tracer velocity with the local magnetic field. Significant differences in turbulent single-particle diffusion in NS and MHD turbulence are not detected. The fluid particle trajectories in the vicinity of the smallest dissipative structures are found to be characterisically different although these comparably rare events have a negligible influence on the statistics investigated in this work.
Europhysics Letters, in print

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Plasma Physics

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http://salesiana.dossiersoluciones.com/handle/123456789/126255

Consulte el texto completo en el siguiente enlace:

https://arxiv.org/abs/physics/0703212
 http://arxiv.org/abs/physics/0703212

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arXiv