On shock evolution and thrust variation of a rocket permeable nozzle in an ascent-descent operation

The unique shock pattern evolution and its corresponding thrust variation of a recently proposed rocket permeable nozzle during an ascent-descent operation are investigated using numerical methods. In the present permeable nozzle flow, the flow pattern and shock system evolution are discussed to demonstrate the flow and hysteresis phenomenon. The formation mechanisms of two featured shocks, permeable shock (PS) and detached shock (DS) are interpreted in two typical scenarios. Accordingly, the interconnection between the nozzle thrust coefficient variation and the shock evolution is clarified. New flow characteristics emerge because of the nozzle permeable section. First, the hysteresis phenomenon manifests through the existence-absence of both the Mach disk and PS/DS. Second, the formation mechanisms of PS and DS differ in low nozzle pressure ratio (NPR, 38.49-134.19) and high NPR (134.19-322.00) scenarios. In the low NPR scenario, PS is formed by the core flow deflection due to ambient air inflow, and the DS detachment is formed by a mild pressure gradient between inflow and backflow. In the high NPR scenario, the PS is formed by the boundary layer re-development after the outflow-induced expansion wave, and the DS detachment is formed by the outflow-induced pressure gradient reduction. Third, the hysteresis of thrust coefficient variation is essentially manifested in a low NPR range. Notably, the hysteresis of PS/DS existence resides well in that of the thrust coefficient, suggesting that their existence plays a vital role in varying the nozzle thrust coefficient.