The two-dimensional magnetohydrodynamic Kelvin-Helmholtz instability: compressibility and large-scale coalescence effects

Abstract

The Kelvin-Helmholtz (KH) instability occurring in a single shear flow configuration that is embedded in a uniform flow-aligned magnetic field, is revisited by means of high resolution two-dimensional (2D) magnetohydrodynamic (MHD) simulations. First, the calculations extend previous studies of magnetized shear flows to a higher compressibility regime. The nonlinear evolution of an isolated KH billow emerging from the fastest growing linear mode for a convective sonic Mach number $M_{cs}=0.7$ layer is in many respects similar to its less compressible counterpart (Mach $M_{cs}=0.5$). In particular, the disruptive regime where locally amplified, initially weak magnetic fields, control the nonlinear saturation process is found for Alfvén Mach numbers $4\simlt M_A \simlt 30$. The most notable difference between $M_{cs}=0.7$ versus $M_{cs}=0.5$ layers is that higher density contrasts and fast magnetosonic shocklet structures are observed. Second, the use of adaptive mesh refinement allows to parametrically explore much larger computational domains, including up to 22 wavelengths of the linearly dominant mode. A strong process of large-scale coalescence is found, whatever the magnetic field regime. It proceeds through continuous pairing/merging events between adjacent vortices up to the point where the final large-scale vortical structure reaches the domain dimensions. This pairing/merging process is attributed to the growth of subharmonic modes and is mainly controlled by relative phase differences between them. These grid-adaptive simulations demonstrate that even in very weak magnetic field regimes ($M_A\simeq 30$), the large-scale KH coalescence process can trigger tearing-type reconnection events previously identified in cospatial current-vortex sheets.

Published in Physics of Plasmas, figures absent due to file sizes, full version at http://www.phys.uu.nl/~toth/ (follow Publications)

References in corpus (1)

• Adaptive mesh refinement for conservative systems: multi-dimensional efficiency evaluation

Cited by in corpus (10)

• The Statistics of Supersonic Isothermal Turbulence
• Formation and long-term evolution of 3D vortices in protoplanetary discs
• Local simulations of the magnetized Kelvin-Helmholtz instability in neutron-star mergers
• Nonlinear evolution of the magnetized Kelvin-Helmholtz instability: from fluid to kinetic modeling
• Effect of dust on Kelvin-Helmholtz instabilities
• The Kelvin-Helmholtz instability in weakly ionised plasmas II: multifluid effects in molecular clouds
• Tracing the merger-driven evolution of active galaxies using the CJF sample
• Relation between current sheets and vortex sheets in stationary incompressible MHD
• Particle orbits at the magnetopause: Kelvin-Helmholtz induced trapping
• Magnetic reconnection and the Kelvin-Helmholtz instability in the solar corona