Transitions in a magnetized quasi-laminar spherical Couette flow

C. Kasprzyk¹ - E. Kaplan² - M. Seilmayer¹ - F. Stefani¹

¹ Helmholtz-Zentrum Dresden--Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany
² Université Grenoble Alpes, CNRS, ISTerre, CS 40700, F-38000 Grenoble Cedex 9, France

Abstract
First results of a new spherical Couette experiment are presented. The liquid metal flow in a spherical shell is exposed to a homogeneous axial magnetic field. For a Reynolds number Re = 1000, we study the effect of increasing Hartmann number Ha. The resulting flow structures are inspected by ultrasound Doppler velocimetry. With a weak applied magnetic field, we observe an equatorially antisymmetric jet instability with the azimuthal wave number m= 3. As the magnetic field strength increases, this instability vanishes. When the field is increased further, an equatorially symmetric return flow instability arises. Our observations are shown to be in good agreement with linear stability analysis and non-linear flow simulations. Figs 6, Refs 15.