Hartmann flow with Braginsky viscosity: a test problem for intercluster plasma

TL;DR

This paper investigates the behavior of a Hartmann layer in gyrotropic plasma with anisotropic viscosity, highlighting the importance of including anisotropic viscosity in simulations of intracluster medium dynamics.

Contribution

It introduces a model for Hartmann flow with Braginsky viscosity, demonstrating the effects of anisotropic viscosity on flow profiles and boundary layer thickness in plasma.

Findings

Velocity sharply rises in a thin boundary layer.

Flow profiles are independent of small isotropic viscosity.

Magnetic field and velocity depend on Hartmann and Lundquist numbers.

Abstract

We consider a Hartmann layer, stationary flow of a viscose and resistive fluid between two plates with superimposed transverse magnetic field, in the limit of gyrotropic plasma, when viscosity across the field is strongly suppressed. For zero cross-field viscosity, the problem is not well posed, since viscosity then vanishes on the boundaries and in the middle of the layer, where there is no longitudinal field. An additional arbitrarily small isotropic viscosity allows one to find magnetic field and velocity profiles which are independent of this viscosity floor and different from flows with isotropic viscosity. Velocity sharply rises in a thin boundary layer, which thickness depends both on the Hartmann number and on the Lundquist number of the flow. The implication of the work is that, in simulating ICM dynamics it is imperative to use numerical schemes which take into account anisotropic viscosity. Although magnetic fields are dynamically subdominant in the ICM they do determine its the dissipative properties, stability of embedded structures and the transition to turbulence.