A new radiation model for tabulated chemistry based on steady state flamelets

Abstract

Radiation heat transfer from gas phase species and soot particles is an important process that needs to be taken into account in numerical simulations of reacting flows for the accurate prediction of the flame structure, species yield and pollutant emission. Previous studies have included radiation effects into the tabulated chemistry approach using solutions to the unsteady flamelet equations. A new radiation model based on steady-state flamelets is proposed. This radiation model is developed based on a time scale analysis of flamelets, showing that radiation is a much slower process than chemistry and mixing in the reaction zone. This distinct time scale separation suggests that radiation could be treated in a quasi-steady fashion. In the procedure described herein, flamelets with different radiation intensities varying from non-radiating to fully radiating are pre-computed with a range of scalar dissipation rates to generate the flamelet library. An enthalpy defect is introduced in the flamelet library as a measure of the departure from the non-radiating flamelet solutions. The proposed radiation model is validated on a well-documented methane/air coflow diffusion flame. Results obtained using the tabulated chemistry approach including radiation effects are compared against experimental measurements, revealing satisfactory agreement.

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