Les modelling of the flame describing function of a lean premixed swirl stabilized flame

The prediction of thermo-acoustic instabilities is of paramount importance for gas turbine combustion systems to meet emission and efficiency targets. In order to predict not only the onset of pressure oscillations, but also their amplitude and, as a consequence, their impact on the engine reliability, the non-linear behavior of the system should be studied. An atmospheric lean premixed combustor investigated at the Technical University of Berlin has been numerically studied for validation purposes. A decoupled approach, separating the acoustic behavior and the nonlinear flame response, which is represented in this work by the Flame Describing Function (FDF), has been used. As the first step, the FDF calculation from Large-Eddy Simulations (LES) has been validated, including the effects of flame stretch and heat loss into turbulence combustion models. Then, frequency-domain calculations using a 3D Helmholtz solver have been carried out, and results have been validated against experimental measurements and self-excited LES simulations.