Stochastic simulations of reacting flows under non-equilibrium conditions in the continuum regime

Direct Simulation Monte Carlo (DSMC), generally utilized for simulating rarefied flows, is used for simulating flows in the continuum regime. This method provides an advantage of simulating flows at a molecular level and hence, treating microscopic phenomena such as molecular transport processes and internal energy exchange through individual collisions. A non-reacting case with Kelvin-Helmholtz instabilities developing in a shear layer under thermal non-equilibrium conditions is simulated and the results are compared with Direct Numerical Simulation (DNS). It is found that DSMC captures the overall flow characteristics accurately even in the continuum regime. Subsequently, cases involving reacting flows are explored with DSMC coupled with traditional models for chemical reactions (namely TCE and QK models). Simulations of equilibrium one-dimensional hydrogen-air deflagration and detonation are performed using two different reaction mechanisms. Both mechanisms produce good results for deflagration compared against freely propagating premixed flame structure. However, for detonations, DSMC does not capture the induction zone accurately, especially when using the QK model in its current form. This discrepancy could arise from the lack of treatment of state-specific reaction cross-sections under non-equilibrium flow conditions. Efforts are under way to include in DSMC the reaction cross-sections obtained from Quasi Classical Trajectory (QCT) calculations.