A radiative transport model for large-eddy fire simulations

Three-dimensional simulations of fires cannot be performed on present-day computers without devising simplifications to the governing equations. One such method is the large-eddy simulation (LES) approach for fires developed at NIST. This method results in computationally efficient fire simulations in which the buoyancy-generated motion of hot gases and smoke is driven by Lagrangian particles that carry the heat released by combustion. Complex geometries are represented by blocking cells interior to a rectangular domain. A P1 approximation to the radiation transport equation was developed to be consistent with the exact transport equation for scenarios based upon this model. An isolated fire plume above a semi-infinite solid with a constant absorption coefficient in each half-space was studied as an example. A direct elliptic solver required only a fraction of the total LES computational cost. Radiative fluxes and intensities from the numerical and exact solutions to the P1 approximation were in excellent agreement.