Effects of shape oscillations on bubble dynamics and coalescence

Abstract

When a bubble is excited by an acoustic field, in addition to the volume oscillation, the bubble may deviate from the spherical shape and undergo shape oscillations. The shape oscillations can be directly caused by the anisotropic pressure or they can be caused by the energy transfer from the volume mode through nonlinear modal couplings. The shape oscillations influence the bubble dynamics in many ways. First of all, shape oscillations can limit the volume responses of the bubble since the onset of shape oscillations can lead to the development of localized large curvature and hence the breakup of the bubble. Second, the resonance coupling between the volume mode and a shape mode can give rise to the occurrence of chaos even when the acoustic forcings are so weak that the bubble oscillates close to its equilibrium radius. Third, the coupling between two or more shape oscillation modes can lead to translational motions of the bubble centroid; this can indirectly affect the bubble coalescence in an acoustic field. Finally, the shape oscillations may influence the coalescence through modifying the short-range attractive forces between two neighboring bubbles.