NDLI: Correspondence Between Uncoupled Flame Macrostructures and Thermoacoustic Instability in Premixed Swirl-Stabilized Combustion

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Taamallah, Soufien Zachary, A. Labry Santosh, J. Shanbhogue Ahmed, F. Ghoniem
Copyright Year	2014
Abstract	In this paper, we conduct an experimental investigation of a confined premixed swirl-stabilized dump combustor similar to those found in modern gas turbines. We operate the combustor with premixed methane-air in the lean range of equivalence ratio ϕ ∈ [0.5–0.75]. First, we observe different dynamic modes in the lean operating range, as the equivalence ratio is raised, confirming observations made previously in a similar combustor geometry but with a different fuel [1]. Next we examine the correspondence between dynamic mode transitions and changes in the mean flame configuration or macrostructure. We show that each dynamic mode is associated with a specific flame macrostructure. By modifying the combustor length without changing the underlying flow, the resonant frequencies of the geometry are altered allowing for decoupling the heat release fluctuations and the acoustic field, in a certain range of equivalence ratio. Mean flame configurations in the modified (short) combustor and for the same range of equivalence ratio are examined. It is found that not only the same sequence of flame configurations is observed in both combustors (long and short) but also that the set of equivalence ratio where transitions in the flame configuration occur is closely related to the onset of thermo-acoustic instabilities. For both combustor lengths, the flame structure changes at similar equivalence ratio whether thermo-acoustic coupling is allowed or not, suggesting that the flame configuration holds the key to understanding the onset of self-excited thermo-acoustic instability in this range. Finally, we focus on the flame configuration transition that was correlated with the onset of the first dynamically unstable mode ϕ ∈ [0.61–0.64]. Our analysis of this transition in the short, uncoupled combustor shows that it is associated with an intermittent appearance of a flame in the outer recirculation zone (ORZ). The spectral analysis of this “ORZ flame flickering” — based on flame chemiluminescence data — shows the presence of unsteady events occurring at two distinct frequency ranges. A broad band at low frequency in the range ∼[1 Hz – 10 Hz] and a narrow band centered around 28 Hz.
Sponsorship	International Gas Turbine Institute
File Format	PDF
ISBN	9780791845691
DOI	10.1115/GT2014-27316
Volume Number	Volume 4B: Combustion, Fuels and Emissions
Conference Proceedings	ASME Turbo Expo 2014: Turbine Technical Conference and Exposition
Language	English
Publisher Date	2014-06-16
Publisher Place	Düsseldorf, Germany
Access Restriction	Subscribed
Subject Keyword	Methane Spectroscopy Emission spectroscopy Combustion Acoustics Chemiluminescence Fuels Flow (dynamics) Geometry Flames Heat Gas turbines Fluctuations (physics) Resonance Combustion chambers
Content Type	Text
Resource Type	Article

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