Effects of bubble gas composition on bubble collapse by an underwater shock wave

It is well known that high-pressure shock waves are generated during the collapse of bubbles, on which an underwater shock wave acts. In this study, the effects of bubble gas composition on the generation of shock waves in a bubble collapse were investigated experimentally. The explosive bubbles were composed of a stoichiometric ethylene-oxygen mixture and a stoichiometric hydrogen-oxygen mixture, whereas the gas compositions of the chemically inert bubbles were air and helium. The initial volume-equivalent radius of the bubble varied from 1.0 to 3.9 mm. The nondimensional maximum pressure of the bubble-generated shock wave was inversely proportional to the non-dimensional distance from the bubble for both explosive and chemically inert bubbles. The proportionality factor for the explosive bubbles was higher than that for the chemically inert bubbles. However, the proportionality factor for the hydrogen-oxygen bubble was slightly lower than that for the ethylene-oxygen bubble. This trend occurred because the high reactivity of the hydrogen-oxygen mixture caused an earlier explosion in the shrinkage stage. Regardless of the bubble composition of the gas, the conversion ratio from the bubble energy to the shock energy increased with decreasing momentum acquired by the water around the bubble.