External Excitation Effects on Combustion Instability in Dual-Burn-Rate Solid Rocket Motors With a Large Aspect Ratio

This study is aimed at addressing combustion instability phenomena observed during the operation of dual-burn-rate Solid Rocket Motors (SRM) with a large aspect ratio. Previously, the acoustic mode of the combustion chamber (induced by external excitation) and the vortex shedding frequency were typically analyzed independently, and the probability of unstable combustion in the SRM was mitigated by decoupling these two frequencies. Nevertheless, the influence of the pressure vibration of the acoustic mode on the flow field remains unclear. The results induced by this influence hold substantial significance for the analysis of the unstable combustion of the SRM triggered by acoustic-vortex coupling. This paper investigated the effects of external excitation on combustion stability by applying low, medium, and high-frequency external perturbations during the initial, middle, and final stages of the motor. The pressure oscillation characteristics induced by external excitation and vortex-driven flow within the combustion chamber were systematically analyzed. The results indicated that external excitation exerted the most significant impact during the initial stage compared to the middle and final stages, leading to intensified pressure oscillations in the combustion chamber. Furthermore, when the intensity of vortex shedding in the flow field is strong, it is more likely to couple with the acoustic field, causing combustion instability in the motor. This research provided the critical insights for predicting combustion instability in the dual-burn-rate SRM with the large aspect ratio and proposed the potential strategies to mitigate and eliminate instability.