On various modeling approaches to radiative heat transfer in pool fires

摘要

Six computational methods for solution of the radiative transfer equation in an absorbing-emitting, nonscatter-ing gray medium were compared for a 2-m JP-8 pool fire. The emission temperature and absorption coefficient fields were taken from a synthetic fire due to the lack of a complete set of experimental data for computing radiation for large and fully turbulent fires. These quantities were generated by a code that has been shown to agree well with the limited quantity of relevant data in the literature. Reference solutions to the governing equation were determined using the Monte Carlo method and a ray-tracing scheme with high angular resolution. Solutions using the discrete transfer method (DTM), the discrete ordinates method (DOM) with both S_4 and LC_(11) quadratures, and a moment model using the M_1 closure were compared to the reference solutions in both isotropic and anisotropic regions of the computational domain. Inside the fire, where radiation is isotropic, all methods gave comparable results with good accuracy. Predictions of DTM agreed well with the reference solutions, which is expected for a technique based on ray tracing. DOM LC_(11) was shown to be more accurate than the commonly used S_4 quadrature scheme, especially in anisotropic regions of the fire domain. On the other hand, DOM S_4 gives an accurate source term and, in isotropic regions, correct fluxes. The M_1 results agreed well with other solution techniques and were comparable to DOM S_4. This represents the first study where the M_1 method was applied to a combustion problem occurring in a complex three-dimensional geometry. Future applications of M_1 to fires and similar problems are recommended, considering its similar accuracy and the fact that it has significantly lower computational cost than DOM S_4.