Cavitation thresholds, free surface and cavity cluster dynamics in liquids at shock wave reflection

Cavitation cluster dynamics and cavitation thresholds under plane short shock waves reflected from the free surface of various liquids is investigated experimentally By means of capacity and light absorption methods it is shown that the free-surface velocity is directly connected to the volume concentration of cavitation bubbles in the cavitating area and an expression for it was found. An effect of the time of contact of water and atmosphere on the dynamics of cavitation development is revealed. It was found that one hour is enough to change the free-surface velocity dynamics from monotonous to oscillating, which is characteristic for spalling damage of metals. High-speed filming showed that in the first case, the bubble distribution over the volume is uniform, while in the second case a dense layer of bubbles is formed under the free surface and partly reflects the rarefaction wave which continues moving freely in the formed liquid layer. This effect is probably associated with the changes in the structure of a near-surface layer due to air saturation. It is shown experimentally that for transformer oil, the previous loading history and the time interval between the experiments are essential considerations and the intensity of cavitation is increased under multiple sequential loading.

By means of the capacitance method, which determines the cavitation thresholds and intensity of avitation processes with high accuracy,the dependence oftho intensity of cavitation processes on water temperature was investigated experimentally. It is shown that the intensity ofcavilaw, processes is extreme and increases with temperature from 18,5 to 42 , dropping to an initial value at 52 and again meressing abruptly from 66. A mechanism which accounts for this phenomenon is proposed.