The Effects of Breakup and Evaporation on Droplet impact with Hypersonic Vehicles

Hypersonic vehicles cruising through the atmosphere at speeds in excess of Mach 6 can be damaged upon impact with water droplets and solid particles (rain, fog, and hail). The complex and highly transient interaction of droplets with the shock structure and boundary layer surrounding these vehicles has presented a challenge for experimental and computational methods. The main challenge in predicting the potential impact of hydrometeors on the vehicle's surface is the behavior of liquid droplets undergoing simultaneous shock-driven breakup and evaporation, particularly as the droplets interact with the complex flow field around the vehicle. The behavior of the droplets during shock-boundary layer interaction, and boundary layer separation/reattachment, and the oblique/bow shockwaves is investigated considering the flow field around different geometries such as a double wedge and a 3D cone-cylinder flare nose tips at hypersonic speeds. A two-way coupled Euler-Lagrangian model supplemented with Kelvin-Helmholtz Rayleigh-Taylor (KH-RT) hybrid model to capture the effects of droplet breakup is developed. Droplet breakup tends to increase the residence time of droplets residing within the swirling vortices formed due to the boundary layer separation and reattachment and increases the probability of droplet impact on the vehicle's surface. A thorough statistical analysis is conducted to identify the conditions at which droplet impact with the surface is maximized, considering the droplet trajectory and kinetic energy near the surface.