Large-eddy simulation of the Darmstadt multi-regime turbulent flame using flamelet-generated manifolds

The Darmstadt multi-regime turbulent flame MRB26b is modelled using the Flamelet-Generated Manifold (FGM) in the context of Large Eddy Simulation (LES). Laminar free-propagating premixed flames are used to build a premixed chemical database, and laminar counter-flow flames are adopted to build a non-premixed and a partially premixed database. A detailed comparison of the LES-FGM results with the experimental data using the three databases is conducted, combining two sub-filter closure models, i.e., the PPDF (Presumed Probability Density Function) and DTF (Dynamically Thickened Flame). It is found that different databases lead to similar modelling of velocity, temperature, mixture fraction and major species (e.g., CH₄, O₂, CO₂ and H₂O). However, the intermediate minor species CO and H₂ are better predicted using the two databases based on counter-flow flames due to a better inclusion of the fuel/air mixing and straining effects. Similar to previous studies, using the DTF model is observed to over-predict CO and H₂. This is revealed to be a combined effect of the artificial flame front thickening and flame wrinkling loss, which is characterized by a lower variance of the progress variable. Comparatively, better minor species predictions are obtained using the PPDF without flame thickening. A correction method is proposed and validated to improve the minor species prediction for the DTF model. The combustion regimes and flame propagation directions are also examined. The results are significant for high-fidelity simulation of multi-regime turbulent flames using the flamelet-tabulated combustion model.