Direct Numerical Simulation of Solid Propellant Combustion in Crossflow

Abstract

A direct numerical simulation (DNS) of a homogeneous ammonium perchlorate/hydroxyl-terminated polybutadiene solid propellant in crossflow was carried out to provide proper boundary conditions to an interior ballistics model. A two-step global finite-rate chemistry model for ammonium perchlorate decomposition and decomposition gas-binder gas reactions was used. An Arrhenius pyrolysis model was used to describe the propellant regression rate. Using strand burn rate data, the DNS model was calibrated by modeling an environment with no crossflow and adjusting thermodynamic properties in the gas/solid to match the measured regression rate. Crossflow Mach numbers were then induced, ranging from At = 0.0 to 0.8, where the calculated regression rates are compared to the base regression rate at M = 0.0. The analysis shows that near-wall vorticity increases with Mach number, but does not significantly reduce the flame to wall stand-off distance. Temperature gradients due to boundary layer compression are shown to dominate the regression rate. The validity of the results was tested by incorporating them into an interior ballistics model to simulate the performance of an actual rocket motor and compare to static test data. A simplified DNS heat-transfer-based analysis is presented and shown to produce similar conclusions.