General characteristic analysis with interphase slip

Derive a general characteristic analysis in the frozen regime of the fluid multiphase HTC system for states with nonzero relative phase velocities, where no closed-form characteristic speeds are available.

Background

The paper discusses the frozen regime of the fluid subsystem, corresponding to infinite interfacial-friction and pressure-relaxation times. When the two phases have equal velocities, the authors provide explicit characteristic speeds, including contact and thermo-acoustic waves. For nonzero relative velocity, however, the characteristic structure is not available in closed form, and the numerical method instead computes an upper bound from the eigenvalues of the quasi-linear matrix evaluated numerically in each cell.