Understanding AP/HTPB composite propellant combustion from new perspectives.

Combustion of the AP/HTPB composite propellant at the mesoscale is simulated by a partitioned numerical framework, in which the unsteady solid-phase conduction, gas-solid interface regression, and gaseous combustion are sequentially calculated on two sets of overlapped grids. The gas-solid interface is traced by the level-set method. The mass and species exchange conditions at the gas-solid interface are converted into source terms by the immersed-boundary method. Effectiveness of the entire framework is justified by applying the integrated solver to a Miller pack example. The predicted burning rates show good agreement with experimental data over a wide range of pressure conditions, and the gas-phase temperature field clearly depicts the final diffusion flame. The flame zone closely above the regressing interface can be identified by the fluctuation of the projected velocity components perpendicular to the main stream direction. Statistical results conditional on Lagrangian tracing of fluid parcels released from the AP and binder parts show distinction between the oxidizer-rich and fuel-rich flames in terms of the reaction intensity and the flame structure. From the algorithm/simulation perspective: a partitioned numerical solution framework is built upon overlapped structured (for the gas phase) and unstructured (for the solid phase) meshes; the level-set approach is used on the unstructured mesh to identify solid-gas interface with complex geometry. From the analysis perspective: the flame front is newly defined in terms of the tangential velocity components; the fuel/oxidizer evolution pattern is analyzed from conditional statistics based on Lagrangian tracing; new insights in heterogeneous combustion include, for instance, effects of pressure on the tangential velocity fluctuation and flame properties conditional on different ingredients. [ABSTRACT FROM AUTHOR]