A comparative study of turbulence models for non-premixed swirl-stabilized flames

The accuracy of turbulent swirl-stabilized flame simulation strongly depends on the choice of turbulence model. In this study, four 3D unsteady turbulence closures, including large eddy simulation, scale-adaptive simulation, and two detached eddy simulation variants, along with four RANS models, including RNG k-epsilon, SST k-omega, transition SST, and RSM, are examined for moderate- and high-swirl case studies. It is observed that the scale-adaptive simulation provides the most accurate results for almost all variables and both swirl conditions in the reactive flow. Only the 3D unsteady models predict the vortex breakdown bubble and flame attachment state correctly. However, based on our error analysis, the flow and composition fields predicted by the RANS models are in acceptable agreement with the experimental fields, especially the ones of transition SST when higher swirl number cases or minor species concentration are of interest. Moreover, it is concluded that the viscosity ratio criterion is a better measure of the local LES quality than the turbulent kinetic energy ratio, and the accuracy of a hybrid simulation may be much more dependent on the ability of the model to operate close to the RANS mode where the grid resolution is not sufficient for a resolving simulation than the fraction of the resolved kinetic energy. Finally, the propriety of the base (RANS) model of a DES for the application of interest is important, such that DES with realizable k-epsilon outperforms the commonly used DES with SST k-omega model.