Transient combustion response of homogeneous solid propellant to acoustic oscillations in a rocket motor

Interactions between acoustic waves and the transient combustion response of a double-base homogeneous propellant in a rocket motor have been analyzed numerically. The analysis extends the previous work on gas-phase flame dynamics to include the coupling with condensed-phase processes. Consequently, a more complete description of propellant combustion response to imposed acoustic oscillations can be obtained. Emphasis is placed on the near-surface flame-zone physiochemistry and its coupling with unsteady propellant burning in an oscillatory environment. The formulation treats complete conservation equations and the finite-rate chemical kinetics in both the gas-phase and subsurface regions. The instantaneous propellant burning rate is predicted as part of the solution. Various distinct features of unsteady heat release arising from propellant combustion response in a motor with forced oscillations are studied systematically. As in the pure gas-phase dynamics of the previous case, the dynamic behavior of the luminous flame plays a decisive role in determining the motor stability characteristics. However, the propellant combustion response may qualitatively modify the temporal evolution of heat-release distribution in the luminous flame and as a result exerts a significant influence on the global stability behavior. The primary flame structure adjacent to the propellant surface is usually little affected by flow oscillation. This may be attributed to the large thermal inertial of the condensed phase, which tends to restrain the temperature variation in the near-surface zone in the present study of laminar flows. The situation with a turbulent flow may be drastically different, as turbulence may penetrate directly into the, primary flame and substantially change the local flame dynamics and transport phenomena.