Application of the Diffuse Interface Multiphase Method for High Temperature and Hypersonic Flows with Phase Change

Multiphase flows occurring at high speeds are relevant to many aerospace applications including reentry of space capsules, degradation of orbital debris, and rocket combustion. This work details the development of a computational framework to capture complex, novel flow features that occur in multiphase flows when there are temperature gradients between the fluid phases, and the fluids change phases based on local thermodynamic conditions. A quasi-conservative positivity preserving solver for the five equation model is used with thermal relaxation to the fully conservative four equation model to capture the temperature gradients and phase change. Consequently, both bubbly and dispersed flows are simulated in a highorder multiphase Navier-Stokes solver. Details of the framework are presented and validated, including the method to capture viscous stresses, heat transfer, and phase transition. A series of axisymmetric interactions between a heated liquid aluminum droplet and a Mach 4 shock are presented. The presence of phase transition at high temperature produces a notable change in the quiescent as well as early shock interaction physics, where sudden phase relaxation yields weaker pressure disturbances within the droplet and thus less potential for cavitation. Droplets of both 230 and 23 microns are simulated until breakup, showing a more notable flattening effect in the case of the smaller droplet. Phase transition has a destructive impact on the outer portions of the droplet during breakup as well as at the aftbody, but largely does not decompose the forebody. Wake physics are captured late into the breakup stage, demonstrating the aptness of diffuse interface solvers for bubbly flow analysis.