Experimental study of transient coupling of PVC formation and flame shape transition in a bi-stable turbulent swirl flame

TL;DRAbstract

The dynamics of a bi-stable swirl flame in a gas turbine model combustor is studied using simultaneous PIV and OH-PLIF at 10 kHz. For most operating conditions, the flames in the combustor either feature a steady V-shape or a steady M-shape. A hydrodynamic instability in the form of the so-called precessing vortex core (PVC) occurs only for the M-shaped flames. For the V-flames, the PVC is suppressed due to radial density gradients at the burner nozzle as shown in an accompanying study (Oberleithner et al., Proc 7th Euro Comb Meeting 2015). At some intermediate operating conditions, bi-stable flames occur where the flame alternates randomly between V- and M-shape. This work investigates a transition from V- to M-shape, focusing on the implied transient formation of a PVC and its role in the transition of flame type. The measurements reveal a sequence of events where the PVC forms before the transition of the flame shape. The sequence starts with a slight lift of the flame root due to a

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