LES EVALUTATION OF NON-LINEAR EFFECTS ON THE DYNAMIC FLAME RESPONSE IN A REAL GAS TURBINE COMBUSTION CHAMBER

Large Eddy Simulations (LES) of a lean swirl-stabilized gas turbine burner are used to analyze the non-linear response of the flame in a real gas turbine engine. For this study, two LES of the same geometry are performed: one where the inlet is acoustically modulated with a low perturbation amplitude in order to obtain a linear response, and one where a high amplitude forcing is applied. The high amplitude forced LES reveals that the averaged mean flame shape changes significantly compared to the linearly forced LES. During the oscillation cycle the flame undergoes strong variations in shape, with a typical mushroom shape roll-up. Based on these predictions, the measured global flame response shows that a high forcing amplitude does not only lead to a change in the amplitude response but also changes its delay quite significantly. Although different, the global gain remains quite similar between the linear and non-linear case. However, local variations of this index clearly point to the non compactness of these flames. This also means that high local gain values have opposite effects in regions where the local time delay changes rapidly. One mechanism by which the two configurations differ is revealed by studying PDF of equivalence ratio. In the non-linear case significantly stronger equivalence ratio perturbations act on the flame.