The stability of shock waves in ionizing and dissociating gases

The stability of strong shock waves in argon and carbon dioxide has been studied in a free-piston shock tube using time-resolved interferometry. Unstable shock fronts have been found to occur close to velocities where (dP/dV)H (where P and V are the pressure and the specific volume behind the shock) on the Rankine-Hugoniot curve is positive due to completion of first ionization or dissociation. Such an instability has been described theoretically by D'iakov (1954). However, his stability limits have not been reached in this case, and this suggests that the linearized perturbation analysis is not accurate for the case of the real shock tube flow.