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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Bifurcations of Self-Excited Ducted Laminar Premixed Flames

[+] Author and Article Information
Lipika Kabiraj1

Department of Aerospace Engineering,  Indian Institute of Technology Madras, Chennai-600036, Indialipikakabiraj@gmail.com

R. I. Sujith

Department of Aerospace Engineering,  Indian Institute of Technology Madras, Chennai-600036, Indiasujith@iitm.ac.in

Pankaj Wahi

Department of Mechanical Engineering,  Indian Institute of Technology Kanpur, Kanpur-208016, Indiawahi@iitk.ac.in

1

Corresponding author.

J. Eng. Gas Turbines Power 134(3), 031502 (Dec 29, 2011) (7 pages) doi:10.1115/1.4004402 History: Received April 30, 2011; Revised May 01, 2011; Published December 29, 2011; Online December 29, 2011

Bifurcation analysis is performed on experimental data obtained from a simple setup comprising ducted laminar premixed conical flames in order to investigate the features of nonlinear thermoacoustic oscillations. It is observed that as the bifurcation parameter is varied, the system undergoes a series of bifurcations leading to characteristically different nonlinear oscillations. Through the application of nonlinear time series analysis to pressure and flame (CH* chemiluminescence) intensity time traces, these oscillations are characterized as periodic, aperiodic, or chaotic oscillations, and subsequently the nature of the obtained bifurcations is explained based on dynamical systems theory. Nonlinear interaction between the flames and the acoustic modes of the duct is clearly reflected in the high speed flame images acquired simultaneously with pressure time series.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the thermoacoustic setup. A, premixed multiple flames. B, open-closed glass duct. C, burner tube. D, decoupler. E, LPG-air premixer. F, traverse. P1, P2, P3: pressure sensors. A top view of the burner is presented as an inset at the top right corner of the figure. All dimensions are in millimeters.

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Figure 2

Stability map of the system indicating the stability regimes of the system for an air flow rate of 4000 ccm

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Figure 3

Bifurcation diagram with respect to flame location (Va at 4000 ccm, Vf at 68 ccm). The block arrows indicate the direction of the change in the flame location. (a) Increasing flame location. (b) Decreasing flame location. Local maxima in the pressure time series have been plotted for each flame location. Inset shows a few cycles of a sample time series, with local maxima marked with black dots.

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Figure 4

Phase portraits (i), Poincaré sections (ii), and frequency spectra (iii) for pressure time series (left panels, (a)) and intensity time series (right panels, (b)) for different types of oscillations, sequentially arranged in the order of their occurrence in the bifurcation diagram in Fig. 3. f1=570.2Hz, f2=366.3Hz. In iia(iii) and iib(iii), the markers a, b, c, and d point to frequencies of 163.6, 202.7, 406.6, and 529.9 Hz, respectively. Properties of acquired data in region V are similar to the attractor in region III and thus have not been shown here.

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Figure 5

Instantaneous flame images for limit cycle oscillations. The tagged dots in the pressure time series correspond to the flame images with the same letter labels.

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Figure 6

Instantaneous flame images for quasi-periodic oscillations. The tagged dots in the pressure time series correspond to the flame images with the same letter labels.

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Figure 7

Instantaneous flame images for frequency-locked oscillations. The tagged dots in the pressure time series correspond to the flame images with the same letter labels.

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Figure 8

Instantaneous flame images for period-2 oscillations. The tagged dots in the pressure time series correspond to the flame images with the same letter labels.

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Figure 9

Instantaneous flame images for chaotic oscillations. The tagged dots in the pressure time series correspond to the flame images with the same letter labels.

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