Instabilities in electrically driven rotating MHD layers

C Mistrangelo,L Bühler

doi:10.1088/1757-899x/228/1/012004

Abstract

Flows of electrically conducting fluids exposed to intense magnetic fields exhibit a common feature i.e. the formation of uniform cores in which electromagnetic forces are dominant. Cores are separated from each other by thin layers that extend along magnetic field lines. Across these parallel layers strong gradients of flow variables are present, which can lead to the onset of instabilities and non-linear flow transitions.In this work we investigate dynamics and stability issues of rotating parallel layers driven by electromagnetic forces caused by the interaction of injected electric currents with an applied magnetic field. The geometry considered consists of two coaxial circular electrodes used for current injection. They are placed in parallel electrically insulating planes perpendicular to a uniform magnetic field. The basic axisymmetric steady state flow, characterized by a rotating velocity jet confined in a parallel layer that connects the rims of the electrodes, is rather well understood. By increasing the driving current above a critical value the basic flow becomes unstable and undergoes a sequence of supercritical bifurcations.

Highlights

Driven magnetohydrodynamic (MHD) flows have been investigated numerically for the experimental configuration used in [1] and a test-section has been manufactured and instrumented to study MHD phenomena observed in the simulations
In this work we investigate dynamics and stability issues of rotating parallel layers driven by electromagnetic forces caused by the interaction of injected electric currents with an applied magnetic field
The aim of the present study is getting an overview of unstable flow patterns that occur when the current injected across the liquid metal layer is increased above a critical value [3] [4]

Summary

Introduction

Driven magnetohydrodynamic (MHD) flows have been investigated numerically for the experimental configuration used in [1] and a test-section has been manufactured and instrumented to study MHD phenomena observed in the simulations. In the past experiments and analytical studies have been carried out to investigate MHD flows, where the fluid is set in motion by electromagnetic forces generated by current injected between a pair of concentric electrodes on the bottom of an electrically insulating container [5] [6] [7]. The Hartmann number Ha gives a non-dimensional measure for the strength of the imposed magnetic field This flow distribution differs from the one described in this work, where cores are stagnant and the induced stationary rotating motion consists of jets confined in an internal parallel layer. An experimental program has been proposed to thoroughly investigate instabilities in electrically driven rotating layers

Formulation of the problem

N v t v

Conclusions and future work