Large-eddy simulation of a counterflow configuration with and without combustion

Abstract

A large-eddy simulation in three dimensions was used to study the flow, mixing fields, and combustion in a counterflow burner. A non-reactive case (air/air jets) and a reactive case (methane/air jets) were investigated. Such a configuration is well suited to study and calibrate models for non-premixed flames because of its simplicity and versatility. In the numerical method, fluctuations of density in space and time were considered to depend only on chemistry, not on pressure. The effect of heat release was included by means of the mixture-fraction formulation. To represent the subgrid scale stresses and scalar flux, a Smagorinsky model was used, in which the Smagorinsky coefficient was determined by the dynamic Germano procedure. An equilibrium chemistry model was used to relate the mixture fraction to density, temperature, and species concentrations. The subgrid distribution of the mixture-fraction fluctuation was presumed to have the shape of a β-function. The computed results were found to be in overall agreement with experimental data for the non-reactive case. For the reactive case, in which a simple combustion model was used, a satisfactory agreement with measured data was achieved. A strong influence of combustion on turbulence mechanisms is apparent.