Assessing subfilter-scale turbulence–radiation interaction in a large-scale ethanol pool fire

Turbulence–radiation interaction (TRI) is an important phenomenon that arises in the numerical simulation of turbulent reacting flows, and it is well recognized that it can be responsible for significant errors in predicted mean or filtered quantities. In this paper, the effect of subfilter-scale (SFS) fluctuations in the calculation of the filtered radiation field, SFS-TRI, is investigated for a 0.5 m-diameter ethanol pool fire. This configuration has been previously studied both numerically and experimentally, although not much attention has been given (neither in this specific flame nor in pool fires in general) to how it is affected by SFS-TRI. Coupled large eddy simulations (LES) are carried out here using the open-source fire dynamics simulator solver for meshes with different levels of grid resolution. The participating medium is treated as non-gray with the weighted-sum-of-gray-gases model. SFS-TRI is either neglected (by evaluating the radiative quantities with the filtered temperature and medium composition), or considered, using for that the optically thin fluctuation approximation alongside an empirical model for the filtered emission, that accounts for the temperature autocorrelation. An extension of this model is also tested, which allows an approximate consideration of the absorption coefficient-temperature cross-correlation; this is the first time that such correlation has been taken into consideration in this type of study. Results show that SFS-TRI has a small effect on the domain-integrated emission and radiation loss, but neglecting it can lead to large errors in local radiative quantities. The local temperature is also mispredicted, and non-negligible errors arise in the calculation of the species concentrations as well. These effects are in general more pronounced for large filter widths.