Flowfield-flame structure interactions in an oscillating swirl flame: An investigation using phase resolved and simultaneous OH-PLIF and stereoscopic PIV measurements

A swirling CH4/air diffusion flame at atmospheric pressure was stabilized in a gas turbine model combustor with good optical access. The investigated flame with a thermal power of 10 kW and an overall equivalence ratio of 0.75 exhibited pronounced thermoacoustic oscillations at a frequency of 295 Hz. The main goal of the presented work was a detailed experimental characterization of the flame behavior in order to better understand the flame stabilization mechanism and the feedback loop of the thermoacoustic instability. OH* chemiluminescence imaging was applied for the determination of the flame shape and as a measure of the heat release rate. Laser Raman scattering was used for the simultaneous detection of the major species concentrations, mixture fraction and temperature. The velocity fields were measured by particle image velocimetry (PIV) or stereo PIV, simultaneously with OH planar laser induced fluorescence. The dynamic pressure in the plenum and combustion chamber was determined by microphone probes. The flow field exhibited a conically shaped inflow of fresh gases and an inner and outer recirculation zone. The flame shape was exceptionally flat with a total height of less than 25 mm. The instantaneous flame structures were dominated by turbulent fluctuations, however, phase-correlated measurements revealed the phase-dependent changes of all measured quantities. The paper presents examples of measured results, characterizes the main features of the flame behavior, explains the feedback loop of the oscillation and discusses the flame stabilization mechanism.