Two-phase flow interactions and combustion of AP/HTPB composite propellant in rocket motors with acoustic oscillations

A two-pathway study has been carried on to investigate the role of aluminum additives in suppressing combustion instability in solid rocket motors. In the first part, a numerical simulation on two-phase non-reacting flow interactions in a solid rocket motor has been conducted to investigate the effect of momentum and thermal exchange on modifying system acoustic balance. An Eulerian-Lagrangian approach is developed to simulate to two-phase flow in the rocket motor. The flowfield of the rocket motor represents a complex, fluid dynamic system with various physics involved. The mutual couplings among organized acoustic oscillations, chaotic turbulent motions and particle dynamics and their collective effect on the motor stability behavior are examined in depth. Along with Salita's work on particle size distribution in rocket motors, it is recognized that the contribution to the damping effect on acoustic oscillations comes mainly from the oxidized aluminum smoke.; In the second part of this work, before investigating distributed combustion of aluminum additives in a rocket-motor environment, a numerical study of the combustion of AP/HTPB composite propellant is conducted to clarify issues related to steady and transient combustion of pure solid propellant. A combustion model is first established by including gas- and condensed-phase coupling to predict burning rate of the composite propellant in rocket-motor environments, which provides a reasonable predication on the propellant burning rate. Based on this model, a comprehensive numerical analysis has extended to the transient combustion of response of AP/HTPB composite propellant to acoustic oscillations in a rocket motor. Computational results indicate that strong interactions between combustion and acoustic oscillations produce entropy waves which significantly change velocity field in flame zone. The oscillatory flame in the gas phase serves as a dipole source for driving instability in the chamber. For the composite propellant, the velocity-coupled combustion response is significant. Specially, unsteady burning-rate evolution may contain a frequency about two times of the frequency in flow oscillation. In addition, mean-flow convection also plays an important role in determining propellant combustion response.