A thickened flame model for large eddy simulations of turbulent premixed combustion

TLDR

When the flame is thickened, the combustion–turbulence interaction is affected and must be modeled. The study develops and validates a subgrid scale model for large‑eddy simulations of turbulent premixed combustion, investigating flame–vortex interactions and introducing an efficiency function to incorporate thickening effects. The model is based on artificially thickened flames with constant laminar flame speed, achieved by reducing the Arrhenius pre‑exponential factor and enhancing diffusion; an efficiency function whose inputs are derived from subgrid turbulence velocity and length scales via similarity assumptions and a dilatation‑exclusion operator is used to incorporate thickening effects, and the combustion model is implemented in a compressible parallel finite‑volume–element solver for hybrid grids to simulate a lateral injections combustor. The model’s predictions agree with available experimental data.

Abstract

A subgrid scale model for large eddy simulations of turbulent premixed combustion is developed and validated. The approach is based on the concept of artificially thickened flames, keeping constant the laminar flame speed sl0. This thickening is simply achieved by decreasing the pre-exponential factor of the chemical Arrhenius law whereas the molecular diffusion is enhanced. When the flame is thickened, the combustion–turbulence interaction is affected and must be modeled. This point is investigated here using direct numerical simulations of flame–vortex interactions and an efficiency function E is introduced to incorporate thickening effects in the subgrid scale model. The input parameters in E are related to the subgrid scale turbulence (velocity and length scales). An efficient approach, based on similarity assumptions, is developed to extract these quantities from the resolved velocity field. A specific operator is developed to exclude the dilatational part of the velocity field from the estimation of turbulent fluctuations. The combustion model is then implemented in a compressible parallel finite volume–element solver able to handle hybrid grids to simulate a lateral injections combustor (LIC). Results are in agreement with the available experimental data.