Unsteady Phenomena in Supersonic Nozzle Flow Separation

This work considers the instability of the jet plume from an overexpanded, shockcontaining convergent-divergent nozzle and attempts to correlate this instability to internal shock-induced separation phenomena. Time resolved wall pressure measurements and Pitot measurements are used as primary diagnostics. For the conditions of this study flow separation is asymmetric resulting in a large separation zone on one wall and a small separation zone on the other wall. Correlations of wall pressures indicate a low-frequency, piston-like shock motion without any resonant tones. Correlations of Pitot pressure with wall pressures indicate strong coherence of shear-layer instability with the shock motion. The likely source of the plume instability is the interaction of unsteady waves generated past the main separation shock with the shear layer of the large separation region.