Have you seen a Riemann solver for 2-phase fluid?
 

i am solving two-phase riemann problem. First, I implemented single-fluid riemann exact solver then i extended it for two-phase fluid riemann exact solver. but when i considered similar but different two-phase gases, it worked well. on the other hand, when i considered absolutely different gas(gamma=1.4 and gamma=7.15), it didn't work. No solution. it resulted from some wrong speed of sound in a heavier gas.

my concern is the gas-liquid compressible flow with a single equation of state described by different gamma.