Further characterization of the disturbance field in a transversely excited swirl-stabilized flame

Transverse instabilities in annular gas turbine combustors are an important problem for both power generation and aircraft applications. These instabilities, also found in afterburners and rocket engines, are manifested as strong acoustic field fluctuations perpendicular to the flow direction. Transverse acoustic waves not only directly perturb the flame, but also couple with nozzle acoustics and inherent fluid mechanic instabilities. As such, the unsteady flow field that disturbs the flame is a complex superposition of transverse and longitudinal disturbances associated with both acoustic and vortical waves. This study closely follows prior work of the authors, which overviewed the disturbance field characteristics of a transversely forced, swirling nozzle flow. Velocity data from a transversely forced, swirl-stabilized flame was taken using high-speed particle image velocimetry (PIV). The topology of the velocity and vorticity field is compared between the in-phase and out-of-phase forcing cases using both filtered and instantaneous data. These data also show that the acoustic and vortical disturbances are comparable in amplitude and, because they propagate at very different speeds, their superposition leads to prominent interference patterns in the fluctuating velocity. Data from both non-reacting and reacting test cases are presented to show that many features of the unsteady shear layers are quite similar.