Non-stationary local thermoacoustic phase relationships in a gas turbine combustor

A framework is presented for analyzing the local instantaneous phase difference between non-stationary heat release rate and pressure oscillations that is appropriate for use in high-pressure liquid-fueled combustors. High-speed OH* chemiluminescence images were used as a qualitative marker of the heat release rate, from which the local phase shift relative to the pressure was calculated using the Hilbert transform technique. Two types of behavior were observed during time sequences with constant amplitude pressure oscillations. For the first behavior, a region with out-of-phase pressure and heat release rate oscillations moved upstream along the nozzle shear layer towards the nozzle. For the second behavior, transitions occurred between out-of-phase oscillations in a region along the centerline and a toroidal region close to the nozzle. For time periods with increasing amplitude pressure fluctuations, in-phase heat release rate and pressure oscillations developed throughout the upstream portion of the combustor. These in-phase oscillations could extend along the burner centerline and towards the downstream portion of the combustor. This behavior is reversed during time periods with decreasing amplitude pressure oscillations; the upstream portion of the combustor transitions to featuring regions with out-of-phase oscillations.