Hysteresis of Shock Train Movement in the Isolator with a Ramp

Abstract

Inside the dual-mode scramjet engine, the shock train will move to a new location when the backpressure changes. Few works focus on the response of the shock train position to the backpressure cyclic variation. This work aims to investigate the behavior of the shock train under such backpressure conditions. Experiments were carried out in a Mach 3 direct-connect facility. The isolator is equipped with a ramp that is used to improve the isolator performance. The static pressures along the wall centerlines were measured. The schlieren imaging was used to provide flow visualization. The results show that a significant hysteresis occurs in the shock train position during the backpressure cyclic variation process. It is found that a large-scale subsonic wake flow region forms behind the ramp when the shock train reaches the ramp trailing edge. The capability of the ramp to retain the existence of the wake flow determines the occurrence of the hysteresis. The effects of the ramp height and width on the hysteresis were examined. Based on the experimental data, the oscillation characteristics were discussed by using wavelet analysis and cross-spectrum analysis. The coupled oscillation between the shock train oscillation and the backpressure oscillation was observed.