Transitions in a magnetized quasi-laminar spherical Couette Flow

TL;DR

This study investigates how increasing magnetic field strength affects flow instabilities in a spherical Couette system with liquid metal, revealing the suppression and emergence of different flow structures consistent with stability analysis and simulations.

Contribution

First experimental observation of flow transitions in a magnetized spherical Couette system aligning with theoretical stability predictions.

Findings

Weak magnetic field induces equatorially anti-symmetric jet instability.

Increasing magnetic field suppresses the anti-symmetric instability.

Stronger magnetic field leads to a symmetric return flow instability.

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 anti-symmetric jet instability with 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.