Numerical investigation of thermoacoustic instability caused by small disturbance in a solid rocket motor

The nonlinear instabilities caused by small disturbances in combustion chambers always trouble solid rocket motors (SRMs) in application. This paper performs numerical simulation of the evolution process from the small disturbance to the unsteady state, even the limit cycle oscillation in a SRM with sidewall-burning-grain. Based on the Large Eddy Simulation (LES) technology, the formulation takes into account the complete conservation equations of mass, momentum, energy, and species concentration, and accommodates finite rate chemical kinetics in the gas phase to obtain more details. The coupling mechanism between oscillators is analysed and the impacts of the small disturbances with various amplitudes and frequencies are discussed comprehensively. The discussion of the limit cycle evolutions with the small disturbance amplitudes variation, provides the insight into the phase locking effects, which have great effects on the SRM stabilities. The results also imply when the frequencies of the small disturbances are commensurate with the acoustic modal frequencies, the systems prone to evolve into limit cycle states. Finally, the forced disturbances are eliminated after the limit cycle states achieved to reveal the coupling mechanism systematically and completely.