Effect of a block on flow oscillations near evaporating solid fuel surface

The stability and combustion behavior in hybrid rockets are significantly affected by the formation of vortex and their interactions. Previous studies show that the change in the flow conditions prior to entering the fuel grain can also alter behaviors of regression rate and pressure fluctuations. This study focuses on the effect of vorticity interactions on the combustion behaviors by controlling the vortex formation in the pre-chamber. In this regard, an obstacle located in front of mass-injection part was used in both combustion tests and numerical simulations. Experiment study showed that the obstacle location affects on the strength of pressure fluctuation and frequency behaviors. Additionally, numerical calculations with large-eddy simulation (LES) turbulent flow model were done to simulate the evolution of flow interactions including vortex dynamics and pressure oscillations in a cylindrical configuration. It was found that flow structure is changed in that momentum and fluctuation are increased near wall, and an additional layer of vorticity is created due to the obstacle which interacts with near-wall vortices generated by mass blowing. Also, due to mass injection through the wall, a number of positive azimuthal vorticity spots are created that effectively squeeze mainstream flow toward the wall.