High speed photographic study of the interaction of cavitation bubbles with a boundary

This paper re-examines the collapse of a single cavitation bubble in front of a boundary. A range of different diameter cavitation bubbles were generated by focusing a pulse from a Q-switched Nd:YAG laser of varying energy. High speed shadow photography and Schlieren techniques are used to visualise the collapse process and the resulting bubble deformation at a distance s from the boundary with high temporal and spatial resolution. A sequence of Schlieren images taken with nanosecond time resolution displays the evolution of the cavity at the distance s from the solid surface. Additionally, the pressure distribution of the oscillating bubble especially in the region of the first collapse was recorded by a thin film transducer which is bonded to a pmma block. Both transducer output signals and Schlieren images confirm the formation of a liquid jet and also indicate the importance of the resulting fluid flow to stresses induced in the solid. In an attempt to visualise the fluid flow a flexible rubber film was placed near an oscillating bubble in free space. As expected jet formation in this case is not observed, however unusual fluid flow effects around the bubble can be seen.