Aeroacoustic Instability in Rockets

Abstract

Current solid-propellant rocket instability calculations (e.g., Standard Stability Prediction Program ) account only for the evolution of acoustic energy with time. However, the acoustic component represents only part of the total unsteady system energy; additional kinetic energy resides in the shear waves that naturally accompany the acousticoscillations. Becausemost solid-rocketmotor combustion chambercone gurationssupport gas oscillations parallel to the propellant grain, an acoustic representation of the e ow does not satisfy physically correct boundary conditions. It is necessary to incorporate corrections to the acoustic wave structure arising from generation of vorticity at the chamber boundaries. Modie cations of the classical acoustic stability analysis have been proposed that partially correct this defect by incorporating energy source/sink terms arising from rotational e ow effects. One of these is Culick’ s e ow-turning stability integral; related terms that are not found in the acoustic stability algorithm appear. A more complete representation of the linearized motor aeroacoustics is utilized to determine the growth or decay of the system energy with rotational e ow effects accounted for already. Signie cant changes in the motor energy gain/loss balance result; these help to explain experimental e ndings that are not accounted for in the present acoustic stability assessment methodology.