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

W.-C. Müller; A. Busse

doi:10.1209/0295-5075/78/14003

All issues

Volume 78 / No 1 (April 2007)

EPL, 78 1 (2007) 14003

Abstract

Issue		EPL Volume 78, Number 1, April 2007


Article Number		14003
Number of page(s)		5
Section		Electromagnetism, Optics, Acoustics, Heat Transfer, Classical Mechanics, and Fluid Dynamics
DOI		https://doi.org/10.1209/0295-5075/78/14003
Published online		22 March 2007

EPL, 78 (2007) 14003

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

W.-C. Müller¹ and A. Busse¹^,2

¹ Max-Planck-Institut für Plasmaphysik - 85748 Garching, Germany
² Theoretische Physik Ia, Universität Bayreuth - 95440 Bayreuth, Germany

Received: 6 December 2006
Accepted: 22 February 2007

Abstract

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 $\tau _{{\rm d}}\lesssim t\lesssim 10 \tau _{{\rm d}}$ , $\tau _{{\rm d}}$ 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 characteristically different although these comparably rare events have a negligible influence on the statistics investigated in this work.

PACS: 47.10.-g – General theory in fluid dynamics / 47.27.-i – Turbulent flows / 52.30.Cv – Magnetohydrodynamics (including electron magnetohydrodynamics)

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