Influence of combustion chamber cavity on structural damping characteristics of solid rocket motors

Solid rocket motors with a large aspect ratio are prone to acoustic instability combustion in the combustion chamber, leading to abnormal engine operation. To gain a clearer understanding and effective suppression of acoustic instability combustion, from the perspective of system damping, damping numerical simulations were conducted using the OSCILOS solver. These simulations were conducted based on acoustic damping theory, compactness assump-tions, and nozzle acoustic boundary conditions, considering different cavity parameters and operating conditions. The variation of damping with the regression of the combustion surface, the influence of different cavity positions and head cavity sizes on the engine damping coefficient, and the impact on acoustic instability were comparatively analyzed. The study found that changing the tail charge to a head charge can significantly increase structural damping at the initial ignition moment by approximately 2 times, provided that the combustion chamber length and acoustic cavity natural frequency remain unchanged. Properly increasing the size of the head cavity can significantly enhance structural damping at the initial ignition moment. The results indicate that reasonably adopting a head cavity in solid rocket motors and appropriately increasing the size of the head cavity according to actual conditions can effectively suppress combustion instability phenomena.