The Separation Pattern Transition Phenomena and Its Effects on the SERN Performance

Abstract

Similar to the axisymmetric rocket nozzle, the Single Expansion Ramp Nozzle (SERN) has different separation patterns when it works under the over-expanded condition, but there are many differences between the separation patterns of SERN and axisymmetric rocket nozzle. In SERN, the main separation pattern is the Restricted Shock Separation (RSS), and the Free Shock Separation (FSS) pattern only appears in a small range of the Nozzle Pressure Ratio (NPR). Different separation patterns and dynamic process of separation pattern transition of SERN are observed both in experiment and numerical simulation results. From the CFD results, it could be found that the performance of SERN changes a lot: the transition of separation makes the most serious influence on the lift, and the least to the pitch moments. Moreover, the performance of SERN has an extremum during the transition because of the effect of main jet impinging on the expansion ramp. The transition occurs during the startup and shutdown of the SERN, but the pressure ratios of the transition are different during the two processes, which leads to a hysteresis loop of the SERN performance.