A Comparison of Angular Discretization Strategies for Modeling Radiative Transfer in Pool Fire Simulations

Abstract

Decoupled radiative heat transfer calculations of 30-cm-diameter heptane pool fire are carried out employing the P1, discrete ordinates (DO), and finite-volume (FV) methods. The DO calculations are performed employing three different quadrature schemes (level symmetric hybrid [LSH], spherical surface symmetrical equal dividing angular quadrature [SSD], and TN). By scaling the soot field in the fire, the performances of the various methods are evaluated at different optical thicknesses by employing highly angularly resolved FV calculations (512 directions) as a reference. Twenty-four angular directions in the DO and FV methods are seen to be adequate to accurately predict the distributions of the divergence of the radiative flux within the fire. The corresponding accuracies of the P1 model are seen to decrease with increase in optical thickness. In the regions away from the fire, the P1 model performs poorly in predicting the axial as well as the radial radiative fluxes, whereas the errors associated with employing coarse angular resolutions in the DO method are seen to increase with soot concentrations and distance from the pool centre. Among the DO and FV models, the accuracies of the axial and radial incident radiative flux predictions outside the fire were more dependent on the angular resolution of the calculations rather than on the particular quadrature set employed in the calculations.