Investigation of the role of turbulent fluctuations on the time-averaged radiative emission in large-scale, turbulent pool fires

Abstract

This paper presents an analysis of turbulence-radiation interaction (TRI) effects on the radiative emission. Correlations and auto-correlations that arise from the time-averaging of the emission term are investigated using global data numerically generated for large-scale ethanol and methanol pool fires. The data corresponds to points in the vicinity of the flame and within the hot gas plume. The numerical calculations consists of high-resolution, fully-coupled, large eddy simulation, with the participating medium is treated as non-gray using the weighted-sum-of-gray-gases model. The results show that TRI can increase the mean radiative emission by more than 100% and the magnitude of its effects is highly correlated to the intensity of temperature fluctuations. The blackbody radiation intensity auto-correlation Ib‾ has the dominant contribution to TRI, followed by the absorption coefficient-blackbody radiation intensity correlation, which is in general more important than the absorption coefficient auto-correlation κP‾. Despite this, considering only fluctuations of temperature within the blackbody radiation intensity is not sufficient for an accurate prediction of the mean radiative emission. An approximation for Ib‾ and another for κP‾ are also tested; while the former performs reasonably well, yielding average errors of around 17%, the latter performs quite poorly, with its associated errors surpassing 100%.