A hypervelocity missile flights underwater at 400 km/h. Propulsion gases (yellow) are ejected in the rocket's wake while water vapor (light blue) is produced at the arrow's rear.
Two interfaces are thus present:
a contact surface separating propulsion gases from vapour,
a phase transition front separating the liquid and its vapour.
The same equations are solved everywhere to deal with these two interfaces and associated flow. The same hyperbolic solver is used everywhere.