LES combustion modeling for high Re flames using a multi-phase analogy

Abstract

In this work we propose a novel model for Large Eddy Simulations (LESs) of high Reynolds moderate Damkohler number turbulent flames. The development is motivated by the need for more accurate and versatile LES combustion models for engineering applications such as gas turbines. The model is based on the finite rate chemistry approach in which the filtered species equations of a reduced reaction mechanism are solved prior to closure modeling. The modeling of the filtered reaction rate provides the challenge: As most of the chemical activity, and thus also most of the exothermicity occurs on the subgrid scales, this model needs to be based on the properties of fine-scale turbulence and mixing and Arrhenius chemistry. The model developed here makes use of the similarities with the mathematical treatment of multi-phase flows together with the knowledge of fine-scale turbulence and chemistry obtained by Direct Numerical Simulation (DNS) and experiments. In the model developed, equations are proposed for the fine-structure composition and volume fraction that are solved together with the LES equations for the resolved scales. If subgrid convection can be neglected the proposed model simplifies to the well-known Partially Stirred Reactor (PaSR) model. To validate the proposed LES model comparisons are made with DNS data of a planar turbulent flame in homogenous isotropic turbulence and experimental data for an axisymmetric dump combustor.