Three-dimensional numerical simulations of phase change effects on shock-droplet interactions

In real propulsion systems, phase change often accompanies shock-droplet interactions, significantly affecting droplet deformation and fragmentation. However, the influence of phase change on shock-droplet interactions, especially considering real fluid effects, remains rarely investigated. In this study, with three-dimensional high-fidelity numerical simulations, we conduct a comprehensive investigation of an n-dodecane droplet embedded in its high-temperature vapor environment under shock wave impacting both with and without phase change. We investigate the effects of phase change on the shock-droplet interactions, including the early-stage wave dynamics, the surface instability development, the droplet deformation and movement, as well as the vortical structure. Under the influence of evaporation, the low-temperature vapor layer formed on the droplet surface reduces the shear forces induced by the high-speed airflow, thereby suppressing the growth of Kelvin-Helmholtz instability waves. In contrast, the vorticity analysis shows that condensation effects promote the generation of negative Q-values, corresponding to an increase in the shear force on the droplet surface, thereby enhancing the development of surface instabilities. The phase-change effects of surface instabilities subsequently alter the dynamics of droplet deformation and movement. Finally, we investigated the effect of Mach number on droplet phase change. As the Mach number decreases, the reduced vapor pressure around the droplet enhances the evaporation rate, leading to a transition from condensation-dominated to evaporation-dominated phase-change conditions.