Vortex Shedding Influence on Hybrid Rocket Pressure Oscillations and Combustion Efficiency

Abstract

Numerical simulation is performed and compared with a firing test of an hybrid rocket engine equipped with a catalyzer. The simulation is performed assuming an axisymmetric flow, unsteady Reynolds-averaged Navier–Stokes equations are solved based on a single-phase flow. Stable pressure oscillations are observed during the firing test and could be explained by the simulation with the formation of large-scale vortices at the end of the fuel grain and in the postcombustion chamber. These vortices transport unburnt fuel to the nozzle and play a major role in the mixing process in the postchamber. Two semi-empirical approaches are applied and provide a good order of magnitude for the frequency and frequency shift during the firing test. Another simulation has been performed with an added oxidizer postchamber injection. It revealed that small-scale vortices along the fuel grain in the baseline case are probably generated by the oscillatory motion of the flow due to pressure fluctuations in the engine.