Measurements of Turbulent Swirl Flame Dynamics in an Ethylene-fuelled Gas Turbine Model Combustor at Elevated Pressure

摘要

In this study, high-bandwidth, laser-based imaging diagnostics were applied to study the structure and dynamics of a series of turbulent, swirl-stabilized flames at equivalence ratios ranging from Φ = 0.45 to 1.2, and pressures ranging from 3 to 7 bars. Stereo-PIV measurements, acquired at 9.3 kHz over periods of approximately 1 second were used to characterize the flow-field near the exit plane of the combustor. OH-PLIF measurements were acquired synchronously with the PIV at a rate of 3.1 kHz. Gradient-filtering was used to identify reaction zones in the images and thereby characterize the mean flame surface density. Comparison of the mean velocity and FSD fields showed that whereas increasing pressure had little effect on the flame structure, variation of the stoichiometry from lean to rich resulted in a major change of flame structure and dynamics. The high bandwidth of these measurements enabled us to perform a phase averaging of the data with respect to the dominant flow-field oscillation (identified via proper orthogonal decomposition). This showed that at lean conditions, the dominant flow-field oscillation is an axial forcing associated with thermoacoustic pulsation. At rich conditions, the dominant oscillation was associated with a processing vortex core in the inner recirculation zone. These results are consistent with prior measurements in a burner with similar geometry at atmospheric pressure.