Effect of Combined Hub/Blade Baffles on the Combustion Stability of a Liquid Rocket Engine
The subject of this paper is high frequency combustion instability in liquid propellant rocket engines, a coupling between the acoustics of the combustion chamber and the combustion process. An analytical model of the stabilization impact of combined radial and hub blades was developed, including nozzle, mean flow, and distributed combustion effects. The velocity potential solution methodology was formulated using an eigenfunction expansion and matching technique. The complex geometry of the blade system requires separate solutions for each compartment and the matching technique allows for the velocity potential as well as the gradient of the potential to match at these interfaces. The energy dissipation of the baffle blades was computed using a corner flow boundary layer model that included viscous and turbulence effects incorporated into an admittance surface integral. Neutral stability curves for a given geometry were computed as a function of the interaction index n and time lag t stability parameters. The sensitivity of the model to the overall engine acoustic oscillation mode, blade number, length, was also computed to show the relative stabilizing effects of the baffle geometry.