Internal flow of an electrostatically levitated droplet undergoing resonant shape oscillation

Experimental evidence of internal dc flow circulation within an electrostat ically levitated, 3.4 mm diameter charged water drop oscillating in shape a t a different amplitude is presented. The axisymmetric shape oscillations w ere excited using a continuously pulsed electrostatic field at the fundamen tal 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 a mplitude without an observable minimum threshold. The implication of the ob served internal flow is discussed with respect to the microgravity research facility and environment. (C) 2000 American Institute of Physics. [S1070-6 631(00)02702-1].