Dynamics of Cavitation Induced by Focused Tandem Shock Waves in Water

Cavitation associated with the generation of shock waves in water was examined. To study these processes, a tandem shock wave generator, which generates two cylindrical pressure waves focused by a metallic parabolic reflector to a common focal region, was developed. The temporal evolution of cavitation generated by shock waves at the focal region was determined experimentally using high-temporal-resolution microphotography for a certain time delay between the first and second shock waves. Observation of the focal area also showed jetting cavitation bubbles with diameters of 100 μm without presence of any rigid boundary. A theoretical model that provides analytical expressions for the temporal evolution of the pressure inside the cavitation bubbles and parameters of the pressure waveform of the second shock wave at the focal area was used to improve the same measurement by PVDF sensor gauges. On the basis of this model, the amplitudes of the compression and rarefaction parts of the second shock wave were determined to be 135 MPa and on the order of -50 MPa, respectively. An estimation of the bubble internal gas concentration and temperature during cavitation development was made. The calculated peak internal temperature reached 1240 K.