Nonsteady burning of periodic sandwich propellants with complete coupling between the solid and gas phases

We develop a mathematical model that describes the unsteady burning of a he terogeneous propellant by simultaneously solving the combustion field in th e gas-phase and the thermal field in the solid-phase, with appropriate jump conditions across the gas/solid interface. The model takes into account th e ammonium perchlorate (AP) decomposition flame, reaction between the AP pr oducts and the binder gases, different properties (density, conductivity) o f the AP and binder, temperature-dependent, gas-phase transport properties, and the unsteady nonplanar regressing surface. Propagation of the latter i s described by using a level-set formulation which gives rise to a Hamilton -Jacobi equation. Numerical studies for a periodic sandwich geometry show t hat the surface evolves unsteadily into a steadily propagating front, and t he effects of various parameters (pressure, stoichiometry, length scale) on the steady propagation speed are discussed. A variety of surface shapes ar e predicted, depending on the parameter values. It is shown that accounting for the full Navier-Stokes equation in the gas phase yields results that d iffer little from those generated when an Oseen model is adopted. (C) 2001 by The Combustion Institute.