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The numerical simulation of the combustion process is a common practice during the combustor design. The accurate simulation of lean flames is a problem of great technical relevance. At these conditions, the flames can be susceptible to strong instabilities as well as local quenching phenomena, which can also alter significantly the flame shape. In this framework, Scale Resolving Simulations (SRS) can provide accurate predictions of the main fluid-dynamic quantities as well as the pollutant concentrations in the turbulent flow-field. In this work, the TECFLAM swirl burner, a premixed unconfined methane-air flame, is simulated with Large Eddy Simulation (LES) using ANSYS Fluent. The turbulent combustion is modelled using the Flamelet Generated Manifold (FGM) formulation both with an Extended Turbulent Flame Closure (ETFC) model to introduce the stretch and heat loss effects on the flame and with the standard Zimont’s Turbulent Flame Closure. A generalized implementation of the ETFC model using a look-up table for the laminar flame speed enables the use of the model for arbitrary conditions. The detailed experimental data allowed a detailed validation of the numerical results, showing that the ETFC model improves significantly the flame shape prediction with respect to the Zimont model. [ABSTRACT FROM AUTHOR]