Jet-Oscillation-Induced Combustion Dynamics in a Multi-Nozzle FLOX^® Combustor

A 12-nozzle FLOX^® combustor is used to generate a full-premixed methane-air flame at ϕ = 0.86 at atmospheric pressure. Combustion stability is examined using 5-kHz simultaneous stereo Planar Image Velocimetry (PIV), OH Planar Laser-induced Fluorescence (OH PLIF) and OH chemiluminescence imaging. Proper Orthogonal Decomposition (POD) of the PIV results from various measurement planes reveals that slow jet oscillations with a characteristic Strouhal number of 0.012 are the dominant fluctuations in the flow field. Jet impingement on and detachment from the walls during jet oscillations are shown to cause the liftoff heights of the flames to increase and decrease. Such changes in flame lift-off heights are also primarily asymmetric among geometrically-symmetric flame pairs. In addition, direct flame-flame interactions are observed as jets collide during oscillations. Dynamic Mode Decomposition (DMD) of the same flow fields is shown able to capture not only the same low-frequency jet-oscillation mode, but also a series of modes spanning the whole resolvable spectrum, which are potential origins of higher-frequency peaks observed in the power spectra of integrated OH chemiluminescence signals.