Three-dimensional heterogeneous propellant combustion

A numerical framework is described which permits the calculation of the three-dimensional combustion field supported by a heterogeneous propellant, allowing for complete coupling between the condensedphase physics, the gas-phase physics, and the unsteady, uneven, regressing surface. A random-packing algorithm is used to construct models of ammonium perchlorate (AP) in hydroxyl-terminated polybutadiene propellants which mimic experimental propellants designed by R. Miller, and these are numerically burnt. Mean burning rates are compared with experimental data for four packs, over a pressure range of 7-200 atm. The effect of the local propellant morphology on the local surface regression speed is examined, with particular attention to the behavior in the neighborhood of large AP particles. At first, these burn slowly and protrude significantly above the surrounding surface, but later they are rapidly consumed and the surface flattens. In all cases, mean burning rates can be accurately calculated using an Oseen approximation for the velocity field, rather than solving the Navier-Stokes equations.