Identification of flame displacement from high frequency thermoacoustic pulsations in gas turbine combustors

Non-compact thermoacoustic pulsations at screech level frequencies are observed in a can-type combustor, which reveal a transverse flame displacement as a driving mechanism. This flame displacement effect is studied via an identification routine to evaluate the oscillatory displacement field from highly time resolved flame OH chemiluminescence recordings. Phase conditioned averaging of the resulting data allows to reconstruct the acoustic oscillation cycle. With this evaluation routine, the resulting heat release modulation can be identified with simple and robust measurement techniques. These flame displacement fields are compared against respective fields from synchronous acoustic PIV measurements to assess the method's applicability. The results show the spatially variable displacement field and its dependence on the acoustic pressure amplitude and phase. Ultimately, the findings of this study allow to decompose the total heat release modulation field obtained from experimental data (available from previous works) into its individual contributions, which are local heat release modulations via the acoustic displacement and density.