Investigation of the Fluid Flow Driven by an Alternating Magnetic Field with Ultrasonic Doppler Velocimetry

We report on an experimental study of the influence of technical frequency pulsating magnetic field on a liquid metal volume. Such single-phase a.c. fields are widely used in metallurgy. Ultrasonic Doppler Velocimetry (UDV) has been used to determine the topology of the flow in a liquid metal column contained in a cylindrical vessel. Profile-scan-rates exceeding 25 Hz permit to acquire sequential time series for different radial co-ordinates which in turn allow to map the statistical properties of the flow. Concerning the sensitivity of UDV it was possible to measure values of the velocity down to a few mm/s. Even the flow is no more laminar in this regime almost any industrial situations are more turbulent. Limited by the maximum current which can be supplied to our magnet a range nearly spanning one order of magnitude of the driving magnetic field strength could be investigated. By that scaling laws derived analytically can be checked over a wide parameter range of industrial interest. The characteristic velocity was estimated from the time averaged mean profile in the centre of the container. Here the maximum absolute values of the vertical velocity component are found throughout the whole vessel in the up-stream in the upper half and the downstream in the lower half. Both local maxima scale nearly perfectly linear with the applied magnetic induction. This characteristic is similar to that of classical turbulent shear flows, even here the skin depth is not large compared to the dimension of the bath.