Large eddy simulation for low frequency oscillations in tail-pipe nozzle solid rocket motors

Based on vortex-acoustic coupling theory, large-eddy simulation with Wall-Adapting Local Eddy-Viscosity subgrid-scale turbulence model and finite element method have been used to study the internal flowfield and acoustic field respectively in a tail-pipe nozzle solid rocket motor with transition section grain configuration. The phenomena that acoustic signals, superimposed on the vortex shedding motions, couple with internal flowfiled is convinced to be one main reason contributing to oscillation in the motor. Low frequencies predominate in the combustion chamber while high frequencies predominate in the tail pipe. Several cases with different geometrical shapes have been presented to investigate the influences of parameters on the low frequency oscillation characteristics. The results indicate that upstream mean velocity and the distance between vortex source and impingement points have cooperative effects on the frequency. Increasing upstream average velocity or the volume of vortex-acoustic coupling cavity could either enhance the potential oscillation amplitude in the combustion chamber. Considering reasonable design point of view, it is concluded that decreasing sudden transition angle of the grain combined with increasing tail-pipe radius could reduce the potential oscillation amplitude.