Including Full Chemistry in Simulations of Turbulent Reacting Flows: Flow-Chemistry Coupling via Flamelet Libraries Based on Elemental Mixture Fractions

Abstract

Real turbulent reacting flows typically involve complex chemical kinetics, with dozens of chemical species undergoing hundreds of simultaneous reactions in an underlying complex turbulent flow. However this creates an unacceptable computational burden, so most such simulations are instead approximated by just a handful of chemical species undergoing a small number of reactions, even though this can greatly limit the fidelity of the simulations. To allow a more accurate approach, formal methods have been developed based on the conservation of atoms under chemical reactions that use the “elemental mixture fraction” to rigorously replace the dozens of chemical species transport equations involving hundreds of reaction terms with a single conserved scalar transport equation. For both equilibrium and non-equilibrium chemistry, this approach allows rigorously-developed “flamelet libraries” to be coupled to local values of the conserved scalar and the scalar dissipation rate from the single conserved scalar transport equation, including full chemical kinetics and even differential diffusion of chemical species. This coupling accounts for heat release effects on the flow and mixing processes as well as on transport coefficients, enabling high-fidelity simulations of complex turbulent reacting flows with full chemistry at far lower computational cost than is possible by approaches based on reduced chemistry models.

WERNER J.A. DAHM

Arizona State University