Simulations of a turbulent line fire with a steady flamelet combustion model coupled with models for non-local and local gas radiation effects

Abstract

The general objective of this study is to develop accurate combustion and radiation models for large eddy simulations (LES) of well-controlled laboratory-scale turbulent fires. The combustion model features a library of flamelet solutions corresponding to steady, laminar, strained diffusion flames. The radiation model features a classical description of non-local radiation phenomena through the Radiative Transfer Equation (RTE). Different treatments of coupled combustion and radiation effects at flamelet scale are considered: a treatment in which local radiation phenomena are neglected inside the flamelet solver; and a treatment in which these phenomena are included inside the flamelet solver and also subgrid-scale turbulence-radiation interactions are included in the RTE solver. This modeling framework is incorporated into the LES solver FireFOAM, developed by FM Global. It is evaluated in simulations of a buoyancy-driven, methane-air, turbulent diffusion flame experimentally characterized by measurements of local temperatures and global flame emissive power. Comparisons between simulated and measured temperatures show significant discrepancies that may be explained by overestimated values of the width of the presumed probability density function representing subgrid-scale variations of mixture fraction. Similar comparisons for the global radiative loss fraction show good agreement provided that local radiation phenomena and turbulence-radiation interactions are included in the model.