Timescale-based frozen nonadiabatic flamelet combustion modeling for rocket engine thrust chambers

The present research work introduces a novel combustion model formulation based on the flamelet concept suitable to investigate characteristic flow conditions in rocket engine thrust chambers. The new approach extends the validity domain of existing flamelet models to fully cover the observed flow conditions by incorporating kinetic rate effects into a state-of-the-art nonadiabatic flamelet manifold. This enables a transition between the fluid dynamic and reaction-rate-dominated combustion regimes, depending on the local Damköhler number of the numerical solution field. The approach is investigated based on a representative rocket engine test case focusing on highly nonadiabatic and de Laval nozzle flow conditions for the propellant combination methane-oxygen. Covering a range of propellant mixture ratios associated with significant variations of the underlying chemical effects, three flamelet combustion-modeling approaches of different manifold complexity are compared to high-fidelity laminar finite rate results based on the full chemical reaction mechanism. The obtained data show that the proposed model formulation is able to deliver a notably higher accuracy in the numerical prediction compared to the existing modeling approaches while retaining high computational efficiency to meet industrial design requirements.