Experimental investigations of a magnetically driven Tornado-like vortex by means of Ultrasound-Doppler Velocimetry

The spin-up of a concentrated vortex in a liquid metal cylinder with a free surface is considered experimentally. The vortex is driven by two flow independent magnetic body forces. A continuously applied rotating magnetic field provides the source of the angular momentum. A pulse of about one order of magnitude stronger travelling magnetic field drives a converging flow that temporarily focuses this angular momentum towards the axis of the container. A highly concentrated vortex forms that produces a funnel-shaped surface depression. In this study we have used some modified settings for the UDV device in order to detect the vertical position of the free surface along the beam line. The main modification was a reduction of the echo detection sensitivity. In this way the echo from microscopic particles was blinded out. Instead, only the position of the strong echo from the free surface was detected and recorded. We explore experimentally the duration, the depth and the conditions of formation of this funnel.