Cavitation phenomena in thin films of Newtonian and non-Newtonian fluids due to rapid bubble expansion

Abstract

We report theoretical work in which the growth of a cavitation bubble within a thin, stretching film of liquid is considered. Numerical simulations of cavitation bubble dynamics are used to explain how the growth of a cavity within a stretching liquid film may result in the development of sufficiently large negative pressures (or tension) within the liquid to damage adjacent surfaces. The results of this study are discussed in terms of the possible consequences of a rapid expansion of a vaporous cavitation bubble in samples of healthy (non-Newtonian) and pathological (essentially Newtonian) synovial fluid. Contrary to previous indications in the literature, non-Newtonian (specifically, shearthinning) behaviour is found to result in significantly enhanced tensions in the pressure waves developed about a growing cavitation bubble. The magnitude of the tensions so developed are compared with estimates of cavitation thresholds (σc) which are obtained from experiments involving the reflection of pulsed ultrasound at a flexible boundary. Under some circumstances the tensions developed about the growing cavity are shown to be commensurate with Gc. The possible consequences of these findings are discussed in terms of cavitation damage to blood vessels or other tissues.