The Transient Evolution of Flow Due to the Excitation Pulse in Oscillating Drop Experiments in Microgravity Electromagnetic Levitation

In oscillating drop experiments, surface oscillations in a molten sample are captured and analyzed to determine the surface tension and viscosity of a melt without the need to contact the liquid sample. In electromagnetic levitation, surface oscillations are initiated using an excitation pulse in the electromagnetic field. The variation in the electromagnetic force field drives rapid acceleration in the melt while also changing the flow pattern. During the quasi-static flow conditions prior to the excitation pulse, the flow displays a “positioner-dominated” flow pattern with 4 recirculation loops in the sample hemisphere. However, the accelerating flow of the excitation pulse transitions into a “heater-dominated flow” pattern in which there are only 2 recirculation loops in the sample hemisphere. Following the excitation pulse, the flow rapidly slows and quickly returns to the conditions present before the excitation pulse. For many combinations of parameters, the transition in the flow pattern results in a very complicated variation in velocity with time; that variation is the topic of this paper.