Unsteady shock waves in inhomogeneous gases

The interaction between a propagating shock wave and the diffusion layer between two gases is investigated theoretically and experimentally. Equations describing the reflection and amplification or absorption of a shock at a contact surface are combined with expressions describing diffusion at the gas-gas interface, and the resulting system is modified by the technique of Chisnell (1955) to obtain an approximate solution which is compatible with finite-difference numerical-computation techniques. Simulation results are presented graphically for combinations of gases with different molecular masses and degrees of freedom and shown to be in agreement with those obtained experimentally in a shock tube of overall length 7.5 m using pressure probes, film thermometers, and schlieren photography. It is found that the waves reflected in the diffusion zone are reflected again as they propagate upstream; this multiple reflection affects the shock wave even outside the diffusion zone and partially compensates the pressure differential.