Responses of combustor surface temperature to flame shape transitions in a turbulent bi-stable swirl flame

Abstract

Turbulent swirl flames are known to exhibit intermittent transitions between V- and M-shapes at certain operating conditions. A diagnostic apparatus based on a commercial highspeed laser system is developed in this work to investigate the influence of such transient phenomenon on the surface temperature of an atmospheric-pressure gas turbine model combustor. The transition of flame shapes is monitored by planar OH laser-induced fluorescence (OH PLIF) at 1-kHz repetition rate. Simultaneously, the same laser beam is used to perform 1-D surface thermometry on the base plate and the bluff body of the combustor, which are coated with Mg4FGeO6:Mn, a commonly used thermographic phosphor (TP). Temperature is inferred from the decay of phosphorescence recorded by a highspeed CMOS camera operated at 70kHz. During transitions between attached (V-) and lifted (M-) flames, pronounced temperature variation as much as 100K is observed on the tip of the bluff body. In the spectral domain, temperature measured during the M-flame period exhibits a peak at 475Hz, in good agreement with the measured frequency of the precessing vortex core (PVC) at the same operating condition. This peak does not appear during the V-flame period when PVC is suppressed. The uncertainty of the measurements and the sensitivity of the technique are discussed in detail.