Computations of Side Loads in a Thrust-Optimized Parabolic Nozzle During High-Altitude Testing

Abstract

The present work is to computationally analyze side loads in a thrust-optimized parabolic nozzle during high-altitude testing. The engine startup and shutdown processes of the Korean Space Launch Vehicle II third-stage rocket engine combustor are examined using three-dimensional time-accurate computations. The generation of side loads is closely related to the transition of the separation pattern due to the nozzle shape. However, the results also show that the side loads are significantly affected by the unique flow features of high-altitude testing, such as the flow entering through the gap between the nozzle and the diffuser, as well as the pressure waves produced by the impact of the diffuser flow breakdown. During the engine startup process, the interaction between the nozzle flow and the entrained flow produces unexpected side loads before the transition of the separation pattern. The first transition process generates two side-load peaks. The second transition does not produce any side loads owing to the smooth transition process, which is caused by the entrained flow acting like a nozzle extension. During the engine shutdown process, the initial pressure wave from the diffuser causes fluctuating side loads. The second pressure wave leads to the transition of the separation pattern, which temporarily increases the magnitude of the side loads.