Combustion modeling in solid rocket motor plumes

Plumes emanating from solid rocket motors (SRM) exhibit flow statistics strongly influenced by complex hydrogen/oxygen/chlorine chemistry. These after burning reactions within the plume have a significant impact onto the infrared (IR) irradiance signature, as well as on the chemical erosion of any active or passive mechanical steering system exposed to the reactive motor plume. As SRM combustion chambers operate at oxidizer-fuel ratios considerably less than stoichiometric, afterburning within the plume shear layer occurs. Asides from the intermediate thermochemical loads of the plume on the launch vehicle, the resulting plume exhaust gases of Ammonium perchlorate (AP) based SRM may also have an impact on ozone layer depletion1,2 in the atmosphere and the biosphere of the launch site.3 Within this study we provide an overview on the currently available combustion mechanism and evaluate their applicability to SRM plume modeling. For a preliminary evaluation, the performance of the considered mechanisms is evaluated using a constant volume reactor. Based on the results an improved 28 reaction skeletal kinetic model is proposed and validated against detailed mechanisms in constant volume reactor test cases and a counter-flowing diffusion flame. Subsequently, selected mechanisms are applied in Reynolds-averaged Navier-Stokes CFD calculations of a small scale AP/HTPB SRM plume test case. From the evaluation of the plume thermochemistry it can be shown that the proposed model offers improved performance at lower computational costs. The results of this study offer a relevant evaluation of the performance of current SRM finite rate chemistry models and their impact on flowfield characteristics and are helpful for future scale-resolved simulations of multispecies, reactive solid-rocket motor plumes.