Intermittent Behavior Caused by Surface Oxidation in a Liquid Metal Flow Driven by a Rotating Magnetic Field

The focus of the experimental and numerical study presented in this article is on the bulk flow within a swirling liquid metal column driven by a rotating magnetic field (RMF), whereas the free surface of the melt was covered by a distinct oxide layer. Flow measurements revealed an anomalous behavior of the flow: Pronounced oscillations of both the primary swirling and the secondary recirculating flow occur spontaneously. This peculiarity can be attributed to the influence of the oxide layer at the surface of the metal. The motion of the covering layer is governed by the strength of the fluid flow and the properties of the layer, and it might exhibit three different states of motion: permanent rotation, intermittent rotation, or the quiescent state. The regime of an intermittent oxide layer rotation reveals a striking influence on the bulk flow of the liquid metal. The amplitude of the velocity oscillations observed seems to be at least one order of magnitude larger than those of turbulent fluctuations in a steady RMF-driven flow. The essential features of the phenomenon observed were reproduced by a simple numerical model.