Investigations of the bulk flow inside a cylindrical liquid metal column generated by diverse AC magnetic fields

This presentation considers various situations where the flow inside a liquid metal column is driven by different configurations of AC magnetic fields. The ultrasonic Doppler method has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both a swirling flow in the horizontal planes and the flow pattern in the radial-meridional plane. In the first part we consider the transient liquid metal flow which is generated inside a cylindrical container by the discontinuous application of a rotating magnetic field (RMF) and the alternating application of subsequent RMF and TMF pulses, respectively. Such new approaches have been recently suggested for melt stirring during solidification of metal alloys in order to control the heat and mass transfer at the solidification front. The second part is concerned with an RMF-driven flow which is influenced by an oxide layer at the free surface of the metallic melt. The oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls. A complex interaction occurs if the both forces are in the same order of magnitude. In that case, our measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk flow. Finally, we study the combination of a travelling and a rotating magnetic field which may generate a specific flow phenomenon in form of a concentrated vortex with properties similar to a tornado. The travelling magnetic field (TMF) creates an intense converging flow at one end of the cylinder whereas the additionally superimposed rotating magnetic field (RMF) with a substantially different frequency sets the flow into rotation. The angular momentum conservation forces the rotation to intensify towards the centre of the converging flow. This phenomenon may be useful to stir floating particles into the melt.