Physics of Acoustic Cavitation

Abstract

A vocabulary useful in describing cavitation in an acoustic field will be defined, and concepts will be introduced to facilitate the interpretation of complex, many-bubble phenomena in terms of single-bubble dynamics. A distinction between stable cavities and transient cavities will be made and the roles of these two limiting types of bubbles in “gaseous” and “vaporous” cavitation will be examined. Under the influence of an acoustic field, cavitation bubbles grow either slowly or explosively from small gas nuclei in a liquid. The conditions determining whether a gas nucleus will become an explosively growing, transient cavity or a slowly growing, stable cavity will be summarized, and the dynamics of the two types of cavities will be contrasted. In particular, a conceptual model of a transient cavity will be proposed, and calculations based on this model will be used to characterize the life history of such a cavity from its nucleation to its catastrophic end. The rationalization of specific cavitation phenomena (such as the erosion of solids and the acceleration of chemical reactions) in terms of the pulsations of a stable cavity or the violent collapse of a transient cavity will be considered. Finally, an attempt will be made to indicate where our understanding of the basic physical processes of cavitation needs to be deepened.