A numerical study of nonlinear instability phenomena in solid rocketmotors

An existing nonlinear instability model has been extended and improved to allow it to more realistically treat the longitudinal shock-wave type of combustion instability frequently encountered in tactical solid rocket motors. Results obtained utilizing this model to investigate limiting amplitude and velocity-coupling phenomena in solid rocket motors are presented. An advanced finite difference integration technique capable of accurately describing shocks and contact discontinuities has been incorporated into the computer program, as well as an improved heat conduction solution, an heuristic velocity-coupling model, and a spectral analysis capability. Solutions demonstrating that limiting amplitude is independent of the characteristics of the initial disturbance are presented, as are results of a preliminary study of nonlinear velocity coupling demonstrating such phenomena as triggering, mean pressure shift, modulated limit cycles, and threshold velocity effects.