Numerical Modeling of Radiative Heat Transfer in Pool Fire Simulations

Abstract

Different approaches to modeling radiative heat transfer in Large Eddy Simulations (LES) of a 38 cm diameter methane pool fire are compared. The P-1 radiation model and the discrete ordinates method are spatially decomposed to solve the radiative transport equation (RTE) on parallel computers. The radiative properties are obtained in the form of mean absorption coefficients from total emissivity data or of spectral absorption coefficients extracted from a narrow band model (RADCAL). The predictions are compared with experimental data. The different approaches are able to predict total radiative heat loss fractions with only a moderate loss of accuracy. However, only the discrete ordinates method is able to qualitatively predict the distributions of the radiative heat flux vectors in regions away from the fire. Results obtained from the calculations performed with the gray property model are very close to those obtained with non-gray calculations. Employing the P-1 radiation model with the gray property model provides adequate coupling between the hydrodynamics and radiative heat transfer while decreasing computational time by about 20% compared to the discrete ordinates method in moderate size grids. The computational savings associated with the P-1 model can become significant in LES calculations that are performed on large computational grids (employing hundreds to thousands of processors) to resolve structures on the scale of the pool diameter. Such resolution is necessary to capture both the large structures on the scale of the pool fire and the smaller regions of air engulfments and visible flame structures that are pivotal to characterizing soot location and temperature.