Taylor-Görtler vortex flows driven by a rotating magnetic field inside a liquid metal column

The spin-up of a fluid in a rotating axisymmetric container is a classical problem in fluiddynamics. Considering a spinning cylinder the viscous forces are responsible to convey the angular momentum from the container walls into the liquid. Therefore, the fluid rotates faster in the boundary layers near the horizontal walls. In those Ekman layers the centrifugal force exceeds the radial pressure gradient and the fluid is driven radial outward. A secondary flow is established which effectively transports the angular momentum to the bulk of the liquid. We consider a circular cylinder filled with a liquid metal which is exposed to a rotating magnetic field (RMF). The magnetic field strength is suddenly increased to B0 and maintained at that value. The magnetic field induces a mainly azimuthal body force, the Lorentz force. This experimental study is concerned with the secondary meridional flow during the time if the fluid spins up from rest. Vertical profiles of the axial velocity have been measured by means of the ultrasound Doppler method. The flow measurements show 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 in form of Taylor-Görtler vortices have been observed just above the instability threshold.