Numerical analysis on oscillation characteristics in a tailpipe nozzle solid rocket motor

Based on vortex-acoustic coupling theory, large-eddy simulation with wall-adapting local eddy-viscosity model and finite element method are carried out to study the internal flowfield and acoustic field, respectively, in a tailpipe nozzle solid rocket motor with transition-section grain configuration. The numerical method by means of a mesh sensitivity analysisis proposed for validation. The instantaneous flowfield characteristicsinthe combustion chamber and tailpipe are analyzed. The excited low frequencies are close to that observed in experiment. The phenomenon in which acoustic signals, superimposed on the vortex-shedding motions, couple with an internal flowfield is proven to be one of the main reasons contributing to oscillation in the motor. According to fast Fourier transform, low frequencies predominate inthe combustion chamber; however, high frequencies predominatein the tailpipe. Dozens of cases with different geometrical configurations are presented to investigate parameters that have impact on the low-frequency oscillation characteristics. The results indicate that the oscillation characteristics are mainly influenced by upstream mean velocity, transition-section angle, distance between vortex source and impingement points, tailpipe radius, and convergence angle of the nozzle.