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
Published online 22 March 2007
EPL, 78 (2007) 14003
DOI: 10.1209/0295-5075/78/14003

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 in final form 22 February 2007; published April 2007
published online 22 March 2007

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.

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

© Europhysics Letters Association 2007