Shock Motion and Flow Instabilities in Supersonic Nozzle Flow Separation

Abstract

This study evaluates the role of shock wave motion on the instability of the plume exiting an over-expanded, convergent-divergent nozzle. An array of wall pressure transducers was used to track the position of the shock in time, and a Pitot probe was used to obtain simultaneous measurement of the total pressure fluctuations at various points in the jet that emerges from the separation shock. Analysis of the shock motion revealed that the shock wave becomes more unstable as it becomes stronger, as evidenced by an increase in the range of motion and in the frequency of large-scale oscillations. For strong shocks, there is a substantial correlation between shock motion and total pressure fluctuation in the plume. Such correlation is absent for relatively weak shocks. The study indicates that shock motion affects the plume instability if the separation shock is very strong, and that other mechanisms govern the plume instability when the shock is relatively weak.