Study on the Transient Flows in a Rocket Nozzle

Typical rocket nozzle flows are often subject to shock-boundary layer interaction during the engine start or shut-down process. The resulting interaction flows appear as two different salient patterns, free shock separation (FSS) and restricted shock separation (RSS), both of which significantly affect the engine thrust performance. In the present study, FSS and RSS structures in a thrust-optimized rocket nozzle were studied using CFD methods. The Reynolds-Averaged Navier?Stokes equations were numerically solved using a fully implicit finite volume scheme based on a two-dimensional axisymmetric geometry. Reynolds stress turbulence model was used to best predict unsteady flow behaviors. The present numerical results were compared with the experimental Schlieren photographs. The unsteady side-load generated by shock-boundary layer interaction during shut-down operations is investigated in detail. The maximum nozzle wall pressure is found during the oscillatory transition from FSS to RSS. Based on the present simulated results, several control strategies to alleviate the undesirable side forces are suggested in terms of step, cavity, blowing and bleeding.