Development and testing of a model for turbulence-radiation interaction effects on the radiative emission

Abstract

A new model to account for turbulence-radiation interaction on the radiation emission in the framework of Reynolds-Averaged Navier-Stokes simulations is proposed and tested. The model’s development is based on Reynolds decompositions of the temperature T and the Planck-mean absorption coefficient κ in the time-averaged radiative emission and on a multi-variable Taylor-series expansion of κ as a function of temperature and species concentration. The relative importance of the terms that arise from these processes are assessed using statistics extracted from high-resolution, fully-coupled large eddy simulations (LES) of large-scale pool fires. All high-order terms are related to resolved quantities or to quantities for which models are already available by curve fitting the LES-generated data. The model presents a total error in directly estimating the radiative emission of about 25%, offering a considerable improvement over existing approximations, which, at best, have total errors above 40%. An expression introduced for the mean absorption coefficient also shows a good accuracy, with an associated total error of 16%. When applied to the solution of the time-averaged radiative transfer equation, the new model again outperforms other approximations, especially in the flame region.