Large-eddy simulation of the Sydney swirling nonpremixed flame and validation of several subgrid-scale models

A methane-air swirling diffusion flame is studied by large-eddy simulation (LES) using second-order moment (SOM) and simplified PDF subgrid-scale (SGS) combustion models, Smagorinsky-Lilly and dynamic kinetic energy (DKE) subgrid-scale ( SGS) stress models. The predictions are validated by the experimental data. For LES statistics, comparison of the predicted axial and tangential time-averaged and root-mean-square (RMS) fluctuation velocities, temperature, RMS fluctuation temperature, CO2 and H2O mass fractions with the experimental results shows that all of the SGS models adopted here give results with only slight differences, but the DKE+SOM models are somewhat better than other SGS models. For instantaneous results, the predicted flame shape with a neck region is in agreement with that observed in experiments. The predicted flame shape and length obtained using the DKE+SOM models are better than those obtained using other SGS models. There are both large-scale and small-scale structures in the swirling flame; combustion reduces the large-scale structures and enhances the small-scale structures.