Fundamental Research on the Dynamics of Cavitation Clouds by a Water Shock Tube.

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This report describes the dynamics of nonspherical cavitation bubbles in liquids which are the components of cavitation clouds. Mathematical formulations have first been made on the dynamics of two bubbles with initially different radii in an incompressible liquid by taking account of the interaction effect of the bubbles and the deformation. The incompressible theory has been developed to a compressible case. The theoretical results have been compared with an experiment made by a water shock tube. The results can be summarized as follows:1. A test computation has been made on the collapse of a single vapour bubble near a plane rigid boundary to cinfirm the validity of the theory, and has been compared with the result of a fully numerical simulation and also with an experiment by a water shock tube. Comparison among them has been proved to be rather good.2. Interaction between two bubbles with initially different radii has been clarified. It has been found that the initially smaller bubble becomes unstable due to the interaction with the initially larger bubble, and may produce an impulsive pressure higher than that from a single bubble under appropriate conditions.3. Nonlinear oscillation of two spherical gas bubbles has been treated by the present theory. It has been elucidated that one bubble oscillates with period-m when another bubble oscillates with the same period. This suggests that both bubbles can be the source of the same frequency components of cavitation noise.Along the line of the present research project, the dynamics of cavitation clouds will be further developed for the future.