Magnetic spherical Couette flow in linear combinations of axial and dipolar fields

TL;DR

This paper investigates axisymmetric fluid flow in a spherical shell under combined axial and dipolar magnetic fields, analyzing shear layer stability and the effects of inertial forces through numerical simulations.

Contribution

It introduces a numerical study of Shercliff shear layer behavior under various magnetic field configurations and inertial effects in spherical Couette flow.

Findings

Outer Shercliff layer becomes destabilized with increased inertia

Inner Shercliff layer remains stable under high inertial effects

Intermediate Shercliff layer is disrupted before time-dependent flow appears

Abstract

We present axisymmetric numerical calculations of the fluid flow induced in a spherical shell with inner sphere rotating and outer sphere stationary. A magnetic field is also imposed, consisting of particular linear combinations of axial and dipolar fields, chosen to make $B_r=0$ at either the outer sphere, or the inner, or in between. This leads to the formation of Shercliff shear layers at these particular locations. We then consider the effect of increasingly large inertial effects, and show that an outer Shercliff layer is eventually de-stabilized, an inner Shercliff layer appears to remain stable, and an in-between Shercliff layer is almost completely disrupted even before the onset of time-dependence, which does eventually occur though.