Post-Shock Expansion Phenomenon in Supersonic Internal Flow

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1. The post-shock expansion phenomenon caused by the interaction of a normal shock wave with a turbulent boundary layer in supersonic internal flows is responsible for the curviness of interacting shock, the flow blockage, and the expansion waves behind the bifurcation shock system. The post-shock expansion appears as the shock-induced separation occurs.2. The post-shock expansion becomes stronger as the flow Mach number as well as the divergence angles of the nozzle or diffuser increases. As the Mach number increases over a critical value, the post-shock expansion transforms into the pseudo-shock pattern.3. The incipient post-shock expansion occurs at nearly constant wall Mach number even the divergence angle of diffuser is varied. It implies that the concept of free interaction observed in a variety of external flows should be also applied to internal supersonic flows.4. The unsteadiness caused by the shock wave/turbulent boundary layer interaction was investigated experimentally. The frequencies of oscillating shock wave in internal flows are much lower than those in external flows. The maximum root-mean-square values of fluctuating pressures increase with an increase in flow Mach number and they are significantly affected by flow separation. A flow model of oscillating shock waves in internal supersonic flows is presented.