Rayleigh-Taylor instability of collapsing bubbles in cryogenic liquids

Abstract

In order to predict the maximum cavitation damage to hydraulic machinery in cryogenic engineering such as turbopumps in liquid rockets, it is essential to know the achievable intensity of bubble collapse. Rayleigh-Taylor instability imposes an extinction threshold for collapsing bubbles and determines the upper limit for the strongest collapse possible. In this study, we numerically investigate this information for collapsing bubbles in liquid oxygen. Our results reveal two distinct features of bubble instability in cryogenic liquids compared with that in water. First, high-order surface distortions are preferably developed on the bubble surface. Second, the bubble is most unstable when it collapses moderately, whereas it is stabilized as the collapse intensity is strengthened. A mechanistic study links these intriguing phenomena to the relatively slow bubble dynamics in cryogenic liquids. In that context, the growth time of the distortions emerges as a pivotal factor for the instability development. Together with the amplification rate, it controls the ultimate mode and amplitude of the instability.