Nonlinear acoustics of combustion instability in solid-propellant rocket motors

Abstract

Combustion instability, a large oscillation of pressure in a combustion chamber, is known to be a major source of rocket failure. A common approach to analyzing combustion instability is to regard it as an acoustical phenomenon in an enclosure, driven by the combustion process occurring in a thin region near the grain (solid propellant). Because of the large pressure excursion associated with combustion instability, it exhibits many salient features of nonlinear wave process such as waveform distortion, shock formation, and even chaotic behaviors. In this paper, a comprehensive analytic model for combustion instability of a solid rocket motor is presented. Our focus is on the way in which nonlinearity manifests itself under complex grain geometry, where the acoustic modes can be either harmonically or anharmonically related. Predictions from the model are compared with the static test data for a few representative rockets.