Effects of Damköhler number on vortex–flame interaction in a gas turbine model combustor

Abstract

The mechanisms of the interaction between a precessing vortex core (PVC) and a turbulent swirl flame in a gas turbine model combustor are investigated experimentally using simultaneous PIV and OH-PLIF at repetition rates up to 10kHz. Three operating conditions with different flow rates corresponding to Damköhler numbers of 1, 0.5 and 0.3 are studied. The flames are mainly stabilized in the shear layer of the inner recirculation zone, where also the PVC is located. The measurements show that for all conditions, the PVC interacts strongly with the flame. Two main effects have been observed: On the one hand, the PVC leads to roll-up of the reaction zone at the flame base. This enhances the supply of heat and radicals to the unburned gas, and thus favors subsequent ignition of the unburned gas. On the other hand, the PVC causes considerable aerodynamic stretch of the reaction zones. This can lead locally to disruption, quenching or extinction of the flame. The strength of the two effects changes significantly when the Damköhler number changes. For the case Da=1, the flame roll-up due to the PVC leads to a strong increase of heat release around the vortex. The stretch rates are relatively low and do not strongly affect the reaction progress. In the case Da=0.5, the PVC initially also causes flame roll-up at the flame base. Subsequently, however, roll-up and propagation of the flame are affected by local disruptions and quenching of the reaction zone due to the increased vortex-induced aerodynamic stretch. Consequently, part of the heat release is delayed and shifted to locations further downstream. For Da=0.3, aerodynamic stretch rates further increase and the reaction zones are even more affected by local disruptions and quenching. The zone of heat release is therefore even further elongated in the direction of the flow.