Viscous forces on acoustically levitated gas bubbles

Abstract

When a gas bubble is subjected to an oscillating acoustic field in a gravitational environment, it seeks a location where time-averaged net force vanishes (‘acoustic levitation’). At this location, the bubble undergoes periodic, coupled volumetric pulsation and translational motion. In this study, we extend the existing inviscid theory of acoustic levitation to include viscous drag forces arising from translational motion. Equilibrium locations are computed and compared with predictions from inviscid theory. It is found that the effects are quite small, producing negligible effect on the levitation position.