(Georgia Institute of Technology, 2010-05-11)
Ma, Hsin-Hsiao (Jim)
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.
(Georgia Institute of Technology, 2008)
Ma, Hsin-Hsiao (Jim)
We present an experimental investigation of the dynamics of an acoustically excited swirl combustor. Simultaneous measurements were taken of the acoustic pressure, mean velocity, CH* and OH* radical chemiluminescence, and OH concentrations through planar laser induced fluorescence (PLIF) over a range of forcing frequencies, amplitudes and nozzle exit velocities. As the flame response grows linearly and monotonically with increasing forcing amplitude, the flame’s behavior becomes more complex at higher levels. The observed dynamics of the flame to some extent occur simultaneously, resulting from a combination of at least five flame/flow processes: (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.