Internal flow of an electrostatically levitated droplet undergoing resonant shape oscillation

Experimental evidence of internal dc flow circulation within an electrostatically levitated, 3.4 mm diameter charged water drop oscillating in shape at a different amplitude is presented. The axisymmetric shape oscillations were excited using a continuously pulsed electrostatic field at the fundamental shape mode frequency (l=2) of the drop. It was found that the speed of the internal dc flow varied quadratically with respect to the oscillation amplitude without an observable minimum threshold. The implication of the observed internal flow is discussed with respect to the microgravity research facility and environment.