This study was designed to test the feasibility of acquiring simultaneous PIV/OH-PLIF measurements at multi-kHz rates in a turbulent swirl flame at pressures relevant to modern industrial gas turbine combustors. To accomplish this, particle image velocimetry (PIV) and planar laser-induced fluorescence of the hydroxyl radical (OH-PLIF) were applied simultaneously at 3 kHz to study the dynamics of a lean partially-premixed turbulent swirl-stabilized flame of natural gas in an optically accessible, high-pressure combustion test rig at 5 bars. With 0.25 mJ/pulse at 283 nm for the OH-PLIF measurements, an average signal-to-noise ratio (SNR) of 4.1 was achieved over a region measuring 20 × 80 mm. Absorption of the excitation laser proved to be the greatest challenge in this study, resulting in a significant variation in SNR from one side of the OH-PLIF images to the other. A procedure based on modeling the absorption according to the mean OH-distribution was used to semi-quantitatively correct for this effect. A gradient-based edge-detection algorithm was used to identify reaction zone locations in the resulting images. These were used to compute mean distributions of the flame surface density.

With 2.5 mJ/pulse at 532 nm for the PIV system, velocity fields measuring 20 × 80 mm were measured at a resolution of 1.25 mm. Consistent with prior measurements in the burner, the flame shows strong thermo-acoustic pulsation, with a peak frequency of 388 Hz. Phase-averages of the PIV and OH^∗ data indicate these pulsations are driven by the same resonant feedback mechanism responsible for thermo-acoustic pulsation in the burner at atmospheric pressure. No evidence of a precessing vortex core, known to dominate the flow-field of the burner at atmospheric-pressure conditions, was observed.