Investigation of a Stiff-Integrator Scheme for High-Speed Reacting Flows

Improvements in the modeling of high-speed reacting propulsion flowfields are sought through the coupling of a stiff integrator to determine chemical reaction rates with a multidimensional CFD code. Detailed chemical kinetics models usually have significantly shorter reaction time scales than the fluid time scales, resulting in stiff governing equations and robustness issues. The present work investigates the application of a stiff ordinary differential equation solver, coupled to a diagonalized alternating-direction implicit scheme to decouple the governing time scales. This coupled ODE-ADI split-operator technique is applied to two high-speed reacting flows using hydrogen/air chemistry. The results from the stiff integrator method are compared to the traditional coupled approach utilizing 8- and 18-step kinetics models. Time-step choice, robustness, and comparison of results between the different solution methods are discussed, along with CPU times.