A comprehensive analysis of combustion instabilities of homogeneous propellants in a rocket motor

A comprehensive numerical analysis has been conducted to study the interactions between acoustic oscillations and combustion of a double-base homogeneous propellant in a rocket motor. The formulation treats the complete conservation equations and accounts for finite-rate chemical kinetics in the gas phase and subsurface reactions. 1) Turbulence closure is achieved by means of a well-calibrated two-layer model taking into account the effect of propellant surface transportation. The governing equations and associated boundary conditions are solved numerically using a fully coupled implicit scheme based on a dual time-stepping integration algorithm. Results of steady-state calculations indicate that the onset of turbulence occurs in the middle of the combustion chamber and substantially modifies combustion wave structure in the downstream region. 2) Turbulence may penetrate into the primary 5ame zone and consequently increase the propellant burning rate, a phenomenon commonly referred to as erosive burning. Interactions between acoustic waves and propellant combustion are studied by imposing periodic pressure oscillations at the chamber exit. The oscillatory flow characteristics are significantly altered by the presence of turbulence due to enhanced momentum and energy transport in the gas phase. The large-amplitude fluctuation of heat release observed in the secondary flame zone for the laminar flow is smeared out by turbulent motions. The primary flame zone plays a more important role in determining motor stability characteristics in the turbulent flow region based on Rayleigh’s criterion. In the condensed phase, a large temperature fluctuation and a deep penetration of the thermal wave take place in the downstream region, leading to a very large burning rate fluctuation.