This work investigates the transition between different flame stabilization modes in a gas turbine model combustor consisting of a linear array of five interacting nozzles, which is representative of advanced designs for next generation engines. Simultaneous multi-kHz repetition rate OH planar laser induced fluorescence and stereoscopic particle image velocimetry were used to examine the hydrodynamics and nozzle-nozzle interactions during the transient flame blowoff and reattachment processes. Two different reactants feeding configurations were designed to isolate the effects of different operating and geometric parameters on the combustor's fuel lean performance. In the first configuration, reactants to each nozzle were fed through a common plenum; while reactants to each nozzle were controlled separately in the second configuration.
The lean blowoff point was tested for different inter-nozzle spacings, by changing the nozzles receiving reactants. The combustor's lean operability was optimized when only two nozzles were operated, as a result of the complex interaction between the cross-nozzle flame transport, fluid dynamic strain field, and the recirculation strength. Nevertheless, blowoff occurred at a relatively constant Damkӧhler number.
The blowoff/reattachment process for an individual flame was initiated in a similar manner to isolated bluff-body stabilized flames, though with cross-nozzle flame interactions providing additional means of re-stabilizing a partially extinguished flame. In the connected plenum configuration, blowoff/reattachment dynamics of the three central nozzles were coupled to each other. Blowoff transitions were preferentially initiated in one of the off-center nozzles, with the transition of subsequent nozzles occurring in a random order. Similarly, the center nozzle tended to be the last nozzle to reattach. However, such temporal coincidence of the blowoff/reattachment transitions were not observed in the individual plenum configuration, suggesting the upstream coupling is significant in the combustor dynamics. A statistical analysis demonstrated that changes in downstream conditions would lead to flow re-distribution inside the connected plenum. Both in-chamber and upstream cross-nozzle interactions are equally important in flame blowoff transitions inside a practical combustor, while the in-chamber cross-nozzle interaction plays a more important role in reattachment transitions.Ph.D
