Flowfield-flame structure interactions in an oscillating swirl flame

A swirling methane-air diffusion flame at atmospheric pressure is 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 exhibits pronounced thermoacoustic oscillations at a frequency of 295 Hz. The main goal of the presented work is a detailed experimental characterization of the flame behavior in order to better understand the flame stabilization mechanism and the feedback loop of thermoacoustic instability. OH* chemiluminescence imaging is applied for determining the flame shape and estimating the heat release rate. Laser Raman scattering is used for simultaneous detection of the major species concentrations, mixture fractions, and temperature. The velocity fields are measured by particle image velocimetry (PIV) or stereo PIV, simultaneously with OH planar laser-induced fluorescence. The dynamic pressure in the combustion chamber is determined by microphone probes. The flow-field exhibits a conically shaped inflow of fresh gases and inner and outer recirculation zones. The instantaneous flame structures are dominated by turbulent fluctuations; however, phase-correlated measurements reveal phase-dependent changes in 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.