Large-eddy simulation of a piloted premixed jet burner

Abstract

A three-stream flamelet/progress variable model is applied to the Sydney piloted premixed jet burner (PPJB). Using experimental data, a prior model evaluation is performed to assess critical modeling assumptions regarding the applicability of this formulation to partially-premixed combustion, the statistical representation of the scalar mixing, and the joint PDF-closure. A Dirichlet distribution, as generalization of the beta distribution, is introduced to represent the interaction between the two mixture fractions that are associated with the fuel, pilot, and coflow streams. Comparisons with experimental data are performed to demonstrate the accuracy of this closure-model. Following this prior model evaluation, the three-stream combustion model is applied to large-eddy simulation, and calculations of all four burner configurations, designated as PM1-{50, 100, 150, 200}, are performed. Through comparisons with experimental data and equilibrium computations it was found that the flow-field is sensitive to the scalar inflow composition, and scalar boundary conditions consistent with experimental measurements were used for all simulations. The effect of wall heat-losses on the temperature and species profiles is assessed in an approximate way, suggesting that species profiles are unaffected by the heat-transfer between pilot and coflow streams. Comparisons of statistical results and thermo-chemical correlations show that the model is capable of predicting flow-field, temperature, and major species profiles. The simulations over-predict the fuel-consumption for PM1-150 and PM1-200, which has also been observed in previous investigations. Aspects regarding model extensions to account for heat-losses and transient extinction/re-ignition processes are discussed.