This study addresses predicting the internal thermochemical state in buoyant fire plumes using largeeddy simulations (LES) with a tabular flamelet library for the underlying flame chemistry. Buoyant fire plumes are characterized by moderate turbulent mixing, soot growth and oxidation and radiation transport. Soot moments, mixture fraction and enthalpy evolve in the LES with soot source terms given by the non-adiabatic flamelet library. Participating media radiation transport is predicted using the discrete ordinates method with source terms also from the flamelet library, and the LES subgrid-scale modeling is based on a one-equation kinetic-energy sub-filter model. This library is generated with flamelet states that include unsteady heat loss through extinction nominally representing radiative quenching. We describe the performance of this model both in the context of a laminar coflow configuration where extensive measurements are available and in buoyant turbulent fire plumes where measurements are more global.
With growing use of carbon fiber-epoxy in transportation systems, it is important to understand fire reaction properties of the composite to ensure passenger safety. Recently, a micro-scale pyrolysis study and macro-scale fire tests were performed using carbon fiber-epoxy at Sandia National Laboratories. Current work focuses on numerical modeling of the material conversion, pyrolysis, and gas-phase combustion that replicate the experiments. Large-eddy simulations (LES) and eddy-dissipation concept (EDC) approach are incorporated in the gas phase along with multiple relevant reaction model methods in the solid phase. The numerical methods that use multi-step pyrolysis rate expressions are validated by thermogravimetric analysis (TGA) results. The pyrolyzed fuel components participate in gas-phase combustion using a turbulent combustion model. The multi-phase combustion capability was further assessed using two cases: a single particle reaction and a solid panel exposed to strong radiant heat. The panel fire test indicates that the model accurately reproduces panel temperature profile while a weaker oxidation is predicted.
A 1-m diameter methane fire plume has been studied using a large eddy simulation (LES) methodology. Eddy dissipation concept (EDC) and steady flamelet combustion models were used to describe interactions between buoyancy-induced turbulence and gas-phase combustion. Detailed comparisons with experimental data showed that the simulation is sensitive to the combustion model and mesh resolution. In particular, any excessive mixing results in a wider and more diffusive plume. As mesh resolution increases, the current simulations demonstrate a tendency toward excessive mixing.