Impact of Stretch and Heat Loss on Flame Stabilization in a Lean Premixed Flame approaching Blow-off

The accurate prediction of the turbulent combustion process in lean burn flames is of primary importance in the design of gas turbine low-emission combustors. In this framework, the correct account for high strain levels, combined with the heat loss of the flame, by numerical tools is of high technical relevance in order to improve the operational flexibility while reducing emissions. In fact, in high Reynolds lean combustion modelling, the quenching effects due to flame front distortion are expected to govern flame behaviour. The present work presents an assessment of the modelling strategies to introduce the stretch effects on the flame in Flamelet Generated Manifold (FGM) model, in both the framework of Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES). At this purpose a premixed swirl burner experimentally studied at Cambridge University was chosen, consisting of a strongly swirling, confined natural gas flame. Results highlight that LES-FGM, coupled with an extended Turbulence Flame Closure model (TFC), succeeds in predicting the main characteristics of the flame at different operating conditions approaching blow-off, thus representing a valid tool to investigate lean burn flames in such context.