Transient Taylor-Görtler vortex flow in a spinning liquid metal

This paper is concerned with a liquid metal flow driven by a rotating magnetic field inside a stationary cylinder. We consider especially the secondary meridional flow during the time when the fluid spins up from rest.
Therefore, we filled a Perspex cylinder with the aspect ratio A=H0/D0=2 with the eutectic alloy GaInSn, which is liquid at room temperature. The filled cylinder is placed concentrically in the magnetic induction system PERM at the Helmholtz-Zentrum Dresden-Rossendorf. The PERM stirrer is equipped with six coils, arranged as pole pairs in order to create a rotating magnetic field with field strength up to 17 mT. The magnetic field frequency was fixed to 50 Hz. The developing flow is investigated experimentally and by direct numerical simulations. The fluid velocities are measured non-intrusively using the ultrasound Doppler velocimetry.
Evolving instabilities in the form of Taylor–Görtler vortices have been observed just above the instability threshold (Ta > 1.5*Tacr). They evolve from local spots near midplane that quickly spread around the whole circumference of the cylinder to form closed rings. Subsequently, the central TG-vortex ring is advected by the secondary flow towards the top or bottom of the vessel. In some cases, the central vortex pair is observed to remain stable at half height of the vessel for a long time. The rotational symmetry may survive over a distinct time even if a first Taylor–Görtler vortex pair has been formed as closed rings along the cylinder perimeter. The transition to a three dimensional flow in the side layers results from the advection or a precession and splitting of the Taylor–Görtler vortex rings. The predictable behaviour of the Taylor–Görtler vortices disappears with increasing magnetic field strength. The numerical simulations agree very well with the flow measurements.