Measurements of an unsteady liquid metal flow during spin-up driven by a rotating magnetic field

This experimental study is concerned with the secondary meridional flow during the time if the fluid spins up from rest. A cylindrical cavity with an aspect ratio of unity is filled with liquid metal and suddenly exposed to an azimuthal body force generated by a rotating magnetic field (RMF). Vertical profiles of the axial velocity have been measured by means of the ultrasound Doppler velocimetry. The flow measurements confirm a theoretical study by Nikrityuk et al. (2005) who suggested the existence of two stages during the RMF-driven spin-up, in particular the so-called initial adjustment phase followed by an inertial phase which is dominated by inertial oscillations of the secondary flow. Evolving instabilities of the double-vortex structure of the secondary flow have been detected at a Taylor number of 1.24´105 confirming the predictions of Grants and Gerbeth (2002). Perturbations in form of Taylor-Görtler vortices have been observed just above the instability threshold.