3-D Simulations of the MHD Kelvin-Helmholtz Instability

Abstract

Strongly sheared flows should be ubiquitous in astrophysics and will often be hydrodynamically Kelvin-Helmholtz (K-H) unstable. This can lead to turbulence and mixing. Most astrophysical environments are electrically conducting, so it is important to understand the role of magnetic fields in the K-H instability. While strong magnetic fields, through their tension, are well known to stabilize the K-H instability, the potential for much weaker fields to modify the nonlinear instability has only recently been recognized. Malagoli et al. (1996), Frank et al. (1996) and Jones et al. (1997) have recently carried out high resolution numerical MHD simulations of the K-H instability for periodic sections of 2.5 dimensional flows, demonstrating clearly that a weak magnetic field can add order during the nonlinear evolution of this instability. This paper describes 3-D simulations confirming the earlier trends and showing the ability of a very weak, large-scale field to provide a significant self-organizational influence that smoothes flows. “Weak” excludes fields creating linear stability or stability through tension during linear instability growth. “Order” means that the flows retain a more laminar character.