Numerical investigation on turbulence-radiation interaction in the UMD turbulent line fires

Abstract

This work aims to study the turbulence-radiation interaction (TRI) in the UMD turbulent line fires with increasing levels of underventilation until strong local extinction occurs. Large eddy simulations (LES) are performed with a radiative flamelet/progress variable model to account for local extinction events. The effects of the resolved-scale and subgrid-scale (SGS) TRI on global radiant fractions and local radiative power are quantified. Results show that the total TRI makes a considerable contribution to radiation for all oxygen concentrations (XO2) tested in this work. Specifically, in the most under-ventilated case of XO2=13% featuring strong local extinction, more than 95% of the global radiant fraction is induced by the TRI. More interestingly, it is found that on a regular LES grid resolving more than 80% of the turbulent kinetic energy, the resolved-scale TRI plays a leading role in the XO2=21% case, while the SGS TRI becomes dominant in the XO2=13% case. Further investigations reveal that the temperature self-correlation and the absorption coefficient-temperature correlation are the key components for TRI, which is confirmed by the corresponding conditional statistics. This study highlights the importance of including an SGS TRI model to accurately predict radiation fields in LES of fires with local extinction.