Three-dimensional unsteady thermocapillary flow under rotating magnetic field

Under a rotating magnetic filed (RMF), the instability of thermocapillary flow and its evolution with increasing Marangoni number (Ma) for semiconductor melt (Pr = 0.01) in a floating liquid bridge model (As = 1) are investigated numerically. Under 5 mT RMF, the thermocapillary flow is steady and axisymmetric with Ma < Mac, and the critical Marangoni number Mac for convection instability is 29.5, which is obtained by the direct numerical simulation. When the Ma is a little bit beyond the Mac, the thermocapillary flow loses stability to become a three-dimensional rotating oscillatory convection, and a periodic oscillation is confirmed by the fast Fourier transform analysis, the oscillatory main frequency decays with increasing Ma. Under 1 mT6 mT RMF, the Mac increases roughly with the magnetic strength except the Mac at 4 mT, where the corresponding change of flow mode after the instability is observed. The oscillatory convection occurs with a smaller Ma in the RMF than that without magnetic field. In addition, no instability toward a three-dimensional steady convection, which is the state of thermocapillary flow without magnetic field after the first instability, is observed under the RMF.