Large-eddy simulation of Cambridge-Sandia stratified flames under high swirl

Abstract

The simulation of turbulent stratified swirling flame has received much attention recently owing to its importance for research on power generation and transportation devices. In this study, we have simulated the Cambridge-Sandia flames under the high swirl flow, i.e., premixed flame (SwB3), moderately stratified flame (SwB7), and highly stratified flame (SwB11) using a large-eddy simulation (LES) framework that integrates the mixed gradient-type dynamic structure model, the modulated gradient model (MGM), and the partially-stirred-reactor combustion approach coupled with a reduced (from GRI-Mech) methane oxidation mechanism. The current LES results are assessed through a comparison with experimental data and reference LES results and show good agreement with the experimental data and an evident improvement compared to the reference results. The adopted LES framework successfully captures the secondary recirculation zones in SwB7 and SwB11. Moreover, the temperature above the central bluff body is predicted well in the present work by setting the temperature profiles on the bluff body according to the experimental data. The MGM predictions indicate that the SGS flux is not directly related to the strain rate in the highly swirling and stratified flame. The stratification promotes the reactions in the reaction zones at the height of 10 mm and shows an evident back-supported combustion mode in the reaction zone. At the height of 30 mm, the effects of the stratification are beginning to fade. At the height of 50 mm, the effects of stratification are no longer prominent.