A Numerical Investigation of the Effect of Cavitation on Hypersonic Shock-Raindrop Interaction and Breakup

This investigation centers on the dynamics of droplet breakup influenced by cavitation under high-velocity shock waves, utilizing detailed multiphase computations through Star-CCM+. The study specifically models the interaction of Mach 2.4 and Mach 5 shock waves with 2mm diameter droplets, employing the Volume-of-Fluid and Full Rayleigh-Plesset cavitation models. Two distinct simulation scenarios were examined: a cavitating scenario using a seed density of 1 ∗1012m^-3 and a seed radius of 2.3 ∗ 10^-5m, and a non-cavitating scenario with a seed density of 1 ∗ 107m^-3 and a seed radius of 1 ∗ 10^-7m. The results indicate that at Mach 2.4, below the critical cavitation Mach number, the impact of cavitation on droplet breakup is minimal, with a cavitating volume fraction of merely 1.9 ∗ 10^-3. In this regime, the breakup is primarily influenced by surface phenomena, such as sheet stripping. However, at Mach 5, above the critical threshold, the cavitation effect becomes substantial, with a maximum vapor volume fraction of 0.327, significantly altering the droplet’s behavior. This scenario suggests the potential initiation of jetting processes, frequently observed in droplet cavitation applications. The study provides insights into the immediate consequences of shock wave-induced cavitation on droplets, elucidating the complex interplay between cavitation, droplet deformation, and breakup patterns. Future work will focus on increasing the cavitation volume fraction for a more accurate representation of droplet behavior during atmospheric entry. The model will be expanded to include a wider range of wave speeds and to examine interactions with both normal and oblique shocks. These advancements are expected to deepen the understanding of droplet-vehicle interactions in high-speed aerodynamic environments, particularly in the context of varying shock wave intensities and orientations.