Dynamics of Acoustic Forcing on Turbulent Flames
Ma, Hsin-Hsiao (Jim)
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This research is motivated by instabilities in lean, premixed, swirl combustors. Two experimental setups including a Bunsen burner and a swirl combustor were used along with visualization methods such as Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) to capture data. Error analysis of the two microphone technique was investigated to accurately record acoustic velocity. The flame transfer function was found and reveals that increasing forcing amplitude does not always yield increasing flame response. Several physical mechanisms that influences flame response were also found at a wide range of experimental conditions and forcing frequencies including: (1) the oscillating velocity of the annular jet, oscillations in (2) position and (3) strength of the vortex breakdown bubble and separation bubble, (4) unsteady liftoff of the flame, and (5) an oscillating turbulent flame speed. These processes generally occur simultaneously, with non-monotonic dependencies upon forcing amplitudes.
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