Reconstructed 3D flame structures in noise-controlled swirl-stabilized combustor |
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Authors: | Mamoru Tanahashi Shohei Inoue Masayasu Shimura Shohei Taka Gyung-Min Choi Toshio Miyauchi |
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Institution: | (1) Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan;(2) School of Mechanical Engineering, College of Engineering, Pusan National University, Busan, 609-735, South Korea |
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Abstract: | Flame structures of turbulent premixed flames in a noise-controlled, swirl-stabilized combustor are investigated to clarify
the mechanism of combustion noise reduction by the secondary fuel injection. Planar laser-induced fluorescence (PLIF) is conducted
for several cases with different secondary fuel injection, and 3D flame structure is reconstructed from PLIF results on multiple
planes. The secondary fuel injection suppresses the fluctuation of high-temperature gas in the recirculation zone and reduces
Reynolds stress and entropy terms in the acoustic sound source. In the flame zone, effects of the injection frequency are
discussed by introducing mean progress variable. The flame brush is very wide for the no control case, whereas it becomes
thin and is confined to a narrow space for the secondary fuel injection cases. The investigated combustor gives minimum sound
level at a relevant fuel injection frequency, which is very low compared with the natural acoustic mode of the combustor.
The flame brush becomes very thin, and self-induced oscillations of the flame brush disappear at this relevant frequency.
The oscillation of the flame brush represents large-scale fluctuation of the mean heat release rate. The relations between
characteristics of flame brush and combustion noise are discussed by introducing instantaneous and dynamical effects of flame
front on the entropy term of the sound source. The secondary fuel injection works for the control of the entropy term in the
sound source because the thin flame brush represents suppression of the instantaneous and dynamical effects. |
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Keywords: | |
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