Detailed modeling of a small-scale turbulent pool fire

• Published in: Combustion and flame Vol. 214; pp. 224 - 237
• Main Authors: Wu, Bifen, Roy, Somesh P., Zhao, Xinyu
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01-04-2020; Elsevier BV
• Subjects: Chemistry; Computational fluid dynamics; Computational grids; Computer simulation; Coupling (molecular); Electric power distribution; Emissivity; Heat flux; Heptanes; Line spectra; Line-by-line; Mathematical models; Monte Carlo ray tracing; Optical thickness; Pool fire; Pool fires; Pyrolysis; Ray tracing; Reacting flow; Soot; Turbulence; Two-equation soot model; Uncertainty; Monte Carlo ray tracing; Two-equation soot model; Pool fire; Line-by-line
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/j.combustflame.2019.12.034

Turbulent pool fires have been studied as a canonical configuration in fire science with wide interest. A numerical study of a small-scale turbulent heptane pool fire is conducted in the present study to understand the interactions and coupling among turbulence, chemistry, soot, and radiation in pool fires. A Monte Carlo ray tracing based radiation solver, with line-by-line spectral models for five gaseous species and soot, is coupled with a fireFOAM-based reacting flow solver to describe the dynamics of the target fire. A 33-species skeletal mechanism is employed to describe the finite-rate chemistry. A two-equation soot model with C2H2 based inception model is incorporated to describe soot dynamics. Turbulence is resolved by the computational grid to avoid the uncertainties in modeling the sub-grid scale stress and turbulence-chemistry-radiation interactions. The computed radiative heat fluxes are directly compared with experimental signals and good agreement is observed. Rarely compared in the literature, the line-of-sight spectral distribution of the emissive power is computed and compared with experimental measurements with excellent match in the 4300 nm CO2-dominant emissive peak. A secondary emissive peak near 3300 nm is absent from the numerical results, which can be attributed to experimental uncertainties and/or insufficient representation of the C-H stretching bonds in the radiation spectral model. The instantaneous flame structures show the presence of abundant hydrocarbon molecules as fuel pyrolysis products. A detailed examination of the chemical and radiative source terms reveals the disproportionate relation between these two source terms, especially when soot is present. Soot radiation is largely optically thin while gas radiation is much thicker in optical depth, as a result of the spatial structures of the flame and the non-grey interactions between gas and soot. With the abundant information provided by the detailed simulation in this study, models for turbulence-chemistry-radiation interactions will be derived in future work.