Soot Modeling in Large Eddy Simulation of Turbulent Buoyant Flames Using the Laminar Smoke Point and the Eddy Dissipation Concept

Abstract

ABSTRACT The paper presents a comprehensive set of Large Eddy Simulations (LES) of turbulent diffusion buoyant flames with a focus on soot modeling. Combustion modeling is based on the Eddy Dissipation Model (EDM) with an infinitely fast chemistry approach. Soot formation and oxidation are modeled with finite-rate chemistry based on the Laminar Smoke Point (LSP) concept. A turbulence-soot interaction model is proposed based on the Eddy Dissipation Concept (EDC) to close the chemical sink/source term for soot. A novel aspect of the modeling is the hybrid EDC formulation, where the mean chemical source term is a weighted average of a laminar term and a turbulent term, based on the local turbulent Reynolds number. The correct limiting behavior in the laminar regime is demonstrated for a laminar ethylene flame. Improvements in soot predictions near the fuel injection are obtained for a 13.7 cm-diameter turbulent ethylene flame and a 30 cm-diameter heptane flame. Additionally, the influence of the combustion model on soot predictions is carefully examined, especially with respect to the mixing time scale formulation and the related influence of the cell size (used as filter width in LES). A proposed dynamic model allows obtaining improved results even in under-resolved simulations and mitigating mesh sensitivity for soot predictions.