Contact zone instability due to real gas effects in shock tube flows

A simple theory is presented to describe the motion of a non-ideal contact surface, or mixing front, during shock tube flow. Under certain conditions, this mixing front is predicted to become trapped within the relaxation zone, and thus destroy shock planarity. Under other conditions, the interaction of the mixing front with the sidewall boundary layer is considered to be responsible for reducing the length of the test sample below that predicted for ideal behavior. The theory compares well with experiments when variations in the mean molecular weight of the test gas are small, and coupling of the inviscid free stream and the boundary layer is weak.