Combustion instability at end of burning in a solid rocket motor

Based on a solid rocket motor (SRM), numerical simulation with linear prediction was carried out to study the pressure oscillation at the end of burning. Acoustic modes and natural acoustic frequencies of combustor chamber were obtained by finite element analysis (FEA) method. The results indicate that the first and second axial acoustic frequencies first decrease and then increase with the regression of the burning surface. The flow-field and pressure oscillation characteristics of the combustor were analyzed via large eddy simulation (LES) method. The oscillation frequency was well consistent with the experimental value, confirming that the SRM presented fundamental acoustic combustion instability. Then the damping effect of the motor was analyzed. It shows that the total damping continuously decrease with the regression of the burning surface. Finally, the pressure oscillation mechanism at the end of burning was explained via linear combustion instability theory. The decrease of the throat-to-port area ratio is a key factor that makes the SRM turn from linear stable state to linear unstable state.