Assessment of subfilter-scale turbulence-radiation interaction in non-luminous pool fires

Abstract

The objective of this work is to investigate the effects of Turbulence-Radiation Interaction (TRI) in Large Eddy Simulation (LES) of ethanol pool fires ranging from medium to large sizes. LES of three pool fires are performed using a steady laminar flamelet (SLF)/presumed Filtered Density Function (FDF) combustion model and the Rank Correlated Full Spectrum k-distribution (RC FSK) for spectral gas radiation. Subfilter-scale (SGS) absorption TRI is neglected whereas the filtered emission term is modelled from the presumed FDF approach. The baseline case is the 0.5 m diameter pool fire investigated experimentally by Fischer et al. (Combust. Flame 70 (1987) 291–306). The two other synthetic pool fires were generated by scaling the pool diameter by factors of 2 and 4 while maintaining the fuel mass burning rate per unit area unchanged. Predictions in terms of temperature, mole fractions of radiating species, flame puffing frequency and radiant fraction are in good agreement with the available experimental data. Model results show that TRI accounts for at least 80% of the radiative loss. For LES that resolves more than 80% of the temperature variance, the SFS TRI contributes for a non-negligible part to radiative loss and its contribution increases significantly with the pool size. Neglecting it affects significantly the predictions of the fire plume structure and radiative heat flux even for medium-scale pool fires.