A model of the effects of pressure and crossflow velocity on composite propellant burning rate

Abstract

Abstract : Several variations of a model for prediction of burning rate versus pressure behavior of unimodal oxidizer composite propellants in the absence of crossflow were developed and evaluated against a set of data for a series of four formulations. Three variants, including one in which an average oxidizer- burning-surface intersectional area concept is employed and two in which allowance is made for geometry and stoichiometry changes as the propellant recedes past an oxidizer crystal, were found to give excellent agreement with data. The former variant was extended to treat multimodal oxidizer formulations, yielding predictions in excellent agreement with data for two additional formulations containing bimodal oxidizer. In the initial development of the erosive burning aspect of the model, columnar diffusion flame bending was assumed to the sole mechanism leading to burning rate augmentation by crossflow. This assumption led to severe underprediction of erosive burning effects. Accordingly, the model was revised through addition of a flow profile analysis for prediction of cross-flow-induced turbulence augmentation of transport properties governing heat feedback from gas flames as well as flame-bending. This revised model was found to yield good agreement with erosive burning data for five of the six formulations tested, but gave higher predicted rates than observed values for the sixth propellant.