Evolution of Unmagnetized and Magnetized Shear Layers

TL;DR

This study uses numerical simulations to explore how weak magnetic fields influence the development and saturation of Kelvin-Helmholtz instabilities in compressible fluids, revealing complex flow behaviors and enhanced momentum transport.

Contribution

It demonstrates that weak magnetic fields alter the flow morphology, reduce the decay rate of eddies with lower resistivity, and increase momentum transport efficiency in shear layers.

Findings

Magnetic fields lead to complex flow structures driven by MHD forces.

Decay rate of eddies decreases with lower resistivity.

Magnetization enhances momentum transport in shear layers.

Abstract

We present numerical simulations of the growth and saturation of the Kelvin-Helmholtz instability in a compressible fluid layer with and without a weak magnetic field. In the absence of a magnetic field, the instability generates a single eddy which flattens the velocity profile, stabilizing it against further perturbations. Adding a weak magnetic field - weak in the sense that it has almost no effect on the linear instability - leads to a complex flow morphology driven by MHD forces and to enhanced broadening of the layer, due to Maxwell stresses. We corroborate earlier studies which showed that magnetic fields destroy the large scale eddy structure through periodic cycles of windup and resistive decay, but we show that the rate of decay decreases with decreasing plasma resistivity, at least within the range of resistivity accessible to our simulations. Magnetization increases the efficiency of momentum transport, and the transport increases with decreasing resistivity.