Investigating the Reacting Flow-Field within a Model Solid Fuel Ramjet Combustor using the Flamelet Progress Variable Approach

The development of flamelet generated manifolds (FGM) for solid fuel combustion applications are presented, using CH4 as a test fuel and C4H6 as the gaseous fuel representation of the pyrolysis species for hydroxyl-terminated polybutadiene (HTPB). An optimized cost function minimization method utilizing the downhill simplex routine is presented as a way to determine the species and weights needed to define the reaction progress variable (Cpv) and is shown to increase the accuracy of looking up information from the the tabulated thermochemical data. The FGMs and optimized Cpv are then used to define the flamelet progress variable (FPV) approach as implemented in a high-fidelity discontinuous Galerkin (DG) solver within the JENRE® Multiphysics Framework. The solutions of the reacting flow field within two model solid fuel ramjet combustors are presented with observations on the effects of reaction on the recirculation zone behind a backward facing step. The FPV approach is capable of decreasing the time-to-solution while still maintaining the detailed combustion dynamics of fully detailed reaction mechanisms. This is vital step towards incorporating numerical simulations in the design process of solid fuel propulsion systems.