Effect of nozzle cavity on resonance in large SRM: Theoretical modeling

Cold gas experiments are used to study the vortex-nozzle interaction, which drives thrust pulsation in solid-rocket motors. The experiments carried out in an axial flow model clearly demonstrate coupling of vortex shedding with acoustical longitudinal resonances of the combustion chamber as observed in actual motors. The amplitudes of the pressure fluctuations correspond to one-thousandth of the static pressure, which is the order of magnitude of the observed pulsations in rocket motors. Experiments show that the cavity formed around the nozzle inlet during combustion is crucial. The pulsation level is proportional to the volume of the cavity. Theory predicts this relationship if we assume vortex-nozzle interaction to be the main source of sound. The proposed analytical model does, however, overestimate the pulsation level by an order of magnitude.