AN EROSION MECHANISM FOR NON-LINEAR INSTABILITY IN THE AXIAL MODES OF SOLID PROPELLANT ROCKET MOTORS,

Abstract : Acoustic instability in a solid fuel rocket engine arises from the interaction of sound waves with the burning propellant. An interesting non-linearity arising from acoustic erosivity is investigated, i.e., the dependence of the burning rate on the magnitude (but not the direction) of the fluctuating gas velocity parallel to the transpiring surface. This non-linearity is of first order in the acoustic amplitude, and so can be significant even when higher-order effects are negligible. A simple calculation of the stability in axial modes is presented to illustrate the phenomenon, and it is shown, for example, that a motor stable at low acoustic amplitudes can be unstable at moderate amplitudes due to the non-linearity of erosion. (Author)