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Gas Turbines: Combustion, Fuels, and Emissions

Studying the Stabilization Dynamics of Swirling Partially Premixed Flames by Proper Orthogonal Decomposition

[+] Author and Article Information
Christophe Duwig

Division Fluid Mechanics, Department of Energy Sciences,  Lund University, 22100 Lund, Sweden

Sébastien Ducruix, Denis Veynante

Laboratoire EM2C, CNRS, UPR 288, 92295 Châtenay-Malabry, France;  Ecole Centrale Paris, 92295 Châtenay-Malabry, France

J. Eng. Gas Turbines Power 134(10), 101501 (Aug 14, 2012) (10 pages) doi:10.1115/1.4007013 History: Received June 15, 2012; Revised June 21, 2012; Published August 14, 2012; Online August 14, 2012

Environmental regulations are continuously pushing lower emissions with an impact on the combustion process in gas turbines (GTs). As a consequence, GT combustors operate in very lean regimes (i.e., at relatively low temperature) to reduce NOx formation. Unfortunately, stabilization becomes a challenge for these lean premixed flames. The extremely unsteady dynamics of swirl stabilized flames present crucial issues and this investigation aim is understanding the interaction of swirl stabilization with large coherent fluctuations inherent to vortex breakdown. The investigation utilizes a simplified cylindrical model combustor consisting of a premixing tube discharging in a larger combustion chamber. Fuel and swirling air are separately injected in the mixing tube so that a partially premixed swirling jet encounters vortex breakdown and allows the partially premixed flame to stabilize. The aforementioned extreme sensitivity of lean partially premixed flames challenges any investigation either for measuring, simulating, or post-processing the case of interest. In this paper, the problem is addressed using large eddy simulation (LES) and planar laser induced fluorescence. The LES data are used to follow the fuel air/mixing along with the fuel combustion evidencing large-scale dynamics. These dynamics are further investigated using proper orthogonal decomposition to identify the role of the premixing stage and of the precessing vortex core in the flame behavior.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Swirler, premixing tube, and combustion chamber (dimensions in mm). The computational domain is showed by a dashed line.

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Figure 2

Characteristics of the swirl generator

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Figure 3

Flame topology by chemiluminescence. Spontaneous emission of the OH* radical.

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Figure 4

Burner regimes, as a function of the air mass flow rate (g s−1 ) and the global equivalence ratio (from Ref. [5])

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Figure 5

Instantaneous acetone PLIF images, regime A, compact flame. (a) Longitudinal cut in the premixing tube. Fluids flow from left to right. The stoichiometric contour Yst  = 0.06 is drawn in yellow. The contour Ycp  = 0.4, symbolizing the propane core, is drawn with a light blue line. (b) Transverse visualizations of the propane mass fraction 5 mm downstream of the premixing tube (from Ref. [5]).

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Figure 6

Instantaneous OH PLIF images, regime A, compact flame. (a) Longitudinal cut in the chamber. Flows go from left to right. (b) Transverse visualizations of reactive zones 2.5 cm downstream of the premixing tube (from Ref. [5]).

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Figure 7

Axial and cross-sectional cuts of the temperature field and propane stoichiometric iso-line (white)

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Figure 8

3D visualizations of the PVC (pressure iso-surface in green) and temperature front (iso-T = 500 K in blue)

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Figure 9

3D visualization of the PVC (pressure iso-surface in green) and stoichiometric surface (in red)

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Figure 10

POD modes for the propane mass fraction field in a longitudinal plane: spatial and temporal

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Figure 11

POD modes for the propane mass fraction field in a cross section plane 0.01 m downstream of the expansion (x = 0.11 m). The colors are similar to Fig. 5.

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Figure 12

Propane mass fraction profile in the premixing tube. LES: line; PLIF: symbol.

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Figure 13

POD modes for the propane mass fraction field in a longitudinal cut covering the premixing tube. The colors are similar to Fig. 5.

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Figure 14

POD modes for the propane mass fraction field in a longitudinal cut covering the premixing tube. The colors are similar to Fig. 5.

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Figure 15

Longitudinal cut of the temperature and methane mass fraction with the stoichiometric line (in white)

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Figure 16

3D visualization of the flame front (iso-surface T = 900 K) colored by the axial velocity. Top: side view; Bottom: front view.

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