Numerical investigation of combustion instability in solid rocket motors under overload conditions

This study investigates the combustion instability phenomena in solid rocket motors (SRMs) through an innovative numerical approach, focusing on the effects of propellant response parameters (k) and overload conditions. A comprehensive numerical method was developed, integrating distributed aluminum combustion and AP/HTPB gas-phase reactions, with the Z-N model employed to describe unsteady propellant combustion. Numerical validation against experimental data demonstrated the model accuracy, with predicted transient pressure variation deviating within 5 % of measured values. The study highlighted the nonlinear nature of combustion instability, with k values exceeding 1.8 leading to complex oscillations, mode transitions, and the formation of limit cycles. Under these conditions, pressure fluctuation amplitudes reached up to 20 % of the average chamber pressure. Additionally, the effects of lateral (20, 50 g) and axial (20, 50 g) overloads on combustion stability were systematically analyzed. Results reveal that overload conditions significantly alter flow field and particle distribution characteristics, and combustion instability were induced at a lower propellant response parameter. Application of a 20 g lateral overload induced asymmetric discrete-phase distribution in the SRM, yielding a 24.8 % increase in particle concentration along the overload vector direction. Combustion instability phenomena were triggered when k was 1.4. Under 20 g lateral overload conditions, the pressure oscillation amplitude exceeded 7.9 % of the mean chamber pressure. Axial overload can also induce combustion instability in the SRM. However, due to the acceleration effect of axial airflow, its influence on particle distribution was weaker compared to lateral overload. The SRM exhibited a pressure oscillation amplitude of merely 6.1 % with a 20 g axial overload. These findings could provide valuable insights into the mechanisms driving combustion instability, offering a foundation for designing more stable and reliable SRMs.