Effect of Swirl on an Unstable Single-Element Gas-Gas Rocket Engine

In this study a series of three-dimensional unsteady reacting flow simulations are used to investigate the effect of swirl on the instability amplitude of a single-element gas-gas rocket combustor. The baseline combustor of interest is unstable because of a fuel cut-off event caused by the high-pressure waves in the combustor. Previous two-dimensional simulations have shown that swirl reduces the amplitude of the pressure oscillations compared with that of the baseline configuration. The current three-dimensional simulations show that swirl is indeed able reduce the amplitude of the instabilities, albeit not to the same extent observed in the two-dimensional simulations. We further observe that the enhanced mixing due to the swirling flow leads to a reduction in the recovery time associated with the fuel cut-off event, thereby allowing the combustor to experience a more continuous heat release. Nevertheless, unlike the two-dimensional case, the three-dimensional simulations show that the flame does not stay anchored to the dump-plane, which explains the higher relative amplitudes in this case.