The effects of the excitation pulse on flow in electromagnetic levitation experiments

Oscillating drop experiments allow the surface tension and viscosity of high temperature and highly reactive melts to be measured without an interface contacting the surface of the molten sample. Surface oscillations are induced by varying the electromagnetic field. The oscillations are measured to determine the surface tension and viscosity from the frequency and damping of the oscillations, respectively. The damping of the oscillations is, however, sensitive to the flow conditions within the melt. Recent advances have allowed transient magnetohydrodynamic models to calculate changes in the internal flow in response to variations in the magnetic field, much like those used to induce surface oscillations. These models show that the excitation pulse drives rapid acceleration within the melt. While the fluid flow may accelerate to speeds above the laminar-turbulent transition, the flow speeds are not sustained for sufficient time periods to allow turbulent flow to develop. Following the excitation pulse, the flow rapidly slows and quickly returns to the conditions present before the excitation pulse.