Analysis of Radiation Modeling for Turbulent Combustion: Development of a Methodology to Couple Turbulent Combustion and Radiative Heat Transfer in LES

Radiation exchanges must be taken into account to improve large eddy simulation (LES) prediction of turbulent combustion, in particular, for wall heat fluxes. Because of its interaction with turbulence and its impact on the formation of polluting species, unsteady coupled calculations are required. This work constitutes a first step toward coupled LES-radiation simulations, selecting the optimal methodology based on systematic comparisons of accuracy and CPU cost. Radiation is solved with the discrete ordinate method (DOM) and different spectral models. To reach the best compromise between accuracy and CPU time, the performance of various spectral models and discretizations (angular, temporal, and spatial) is studied. It is shown that the use of a global spectral model combined with a mesh coarsening (compared with the LES mesh) and a minimal coupling frequency $Nit$ allows to compute one radiative solution faster than $Nit$ LES iterations while keeping a good accuracy. It also appears that the impact on accuracy of the angular discretization in the DOM is very small compared with the impact of the spectral model. The determined optimal methodology may be used to perform unsteady coupled calculations of turbulent combustion with radiation.