FLAME AND FLOW TOPOLOGIES IN AN ANNULAR SWIRLING FLOW

This article describes an investigation of flame shapes and flow configurations in a premixed, swirl-stabilized dump combustor. High swirl, annular nozzle flows of this nature enable a variety of different flame configurations and heat release distributions with their associated flow fields. These differences are significant, since each of these configurations, in turn, has different thermoacoustic sensitivities and influences on combustor emissions, nozzle lifetime, and liner heating. These different configurations arise because multiple flame stabilization locations are present, associated with the inner and outer shear layers of the annulus, and the stagnation point of the vortex breakdown region. We present results from highspeed luminosity imaging, particle image velocimetry (PIV), and OH-planar laser induced fluorescence (PLIF) to illustrate time-averaged and instantaneous flame shapes and flow fields associated with the different configuration "families." Selected cases are compared with large eddy simulations (LES). Particular emphasis is given to the distinctly different flame and flow topologies that exist in these flows, and their sensitivity to geometric (such as centerbody size and shape, combustor diameter, exhaust contraction) and operational (e.g., bulkhead temperature, preheat temperature, fuel/air ratio) parameters. We particularly emphasize the importance of the centerbody shape, and its associated impact on the structure of the central recirculating flow, as differentiating between two different families of flame shapes.