Confinement-Induced Instabilities in a Jet-Stabilized Gas Turbine Model Combustor

Self-sustained jet flapping is observed in a confined, premixed and preheated methane-air turbulent flame, generated in a single-nozzle jet-stabilized gas turbine model combustor designed based on the FLOX (a"c) concept. The flapping frequency and its complex motion within the confinement of the combustor are characterized in detail using proper orthogonal decomposition (POD) of the flow fields measured by particle imaging velocimetry (PIV). The influence of jet flapping on combustion stability is examined using simultaneous PIV/OH chemiluminescence imaging and PIV/planar laser-induced fluorescence of OH radicals (OH PLIF) at 5 kHz repetition rate. By influencing the size and location of the recirculation zones, jet flapping modifies the flame shape and flame lift-off height. It also controls the amount of hot gas entrainment into the recirculation zones. In extreme cases, jet flapping is found to cause temporary local extinction of the flame, due to jet impingement on the combustor wall and partial blockage of burned gas entrainment. The flame is only able to recover after the jet detaches from the wall and reopens the back flow channel. The results suggest that jet flapping could play a key role in the stabilization mechanisms in similar jet-stabilized combustors.