  An analysis of the turbulence-radiation interaction in the framework of large
eddy simulation (LES) is presented. Direct numerical simulation (DNS) of
statistical steady forced homogeneous isotropic turbulence is used to evaluate
the relevance of the unclosed terms of the filtered radiative transfer equation
(RTE) and to study the influence of parameters like the optical thickness and
the turbulence intensity. LES without subgrid-scale models of the filtered RTE
has also been investigated. Neglecting the subgrid-scale fluctuations of
radiation has proved to be an accurate assumption in various cases, especially
for the absorption terms of radiation. However, turbulence-radiation
interaction effects increase significantly with the optical thickness based on
the size of the filter or with the turbulence intensity, and consequently
subgrid-scale modelling should be developed in cases where the optical
thickness is not thin and the turbulence intensity higher than 20%.
