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TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

Nonlinear Flame Transfer Function Characteristics in a Swirl-Stabilized Combustor

[+] Author and Article Information
Benjamin D. Bellows1

School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0150, Senior Aerothermal Engineer, Pratt & Whitney Military Engines, 400 Main Street, M/S 184-28, East Hartford, CT 06108benjamin.bellows@pw.utc.com

Mohan K. Bobba, Jerry M. Seitzman, Tim Lieuwen

School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0150

1

Corresponding author.

J. Eng. Gas Turbines Power 129(4), 954-961 (Dec 22, 2006) (8 pages) doi:10.1115/1.2720545 History: Received November 10, 2006; Revised December 22, 2006

An understanding of the amplitude dependence of the flame response to acoustic excitation is required in order to predict and/or correlate combustion instability amplitudes. This paper describes an experimental investigation of the nonlinear response of a lean, premixed flame to imposed acoustic oscillations. Detailed measurements of the amplitude dependence of the flame response were obtained at approximately 100 test points, corresponding to different flow rates and forcing frequencies. It is observed that the nonlinear flame response can exhibit a variety of behaviors, both in the shape of the response curve and the forcing amplitude at which nonlinearity is first observed. The phase between the flow oscillation and heat release is also seen to have substantial amplitude dependence. The nonlinear flame dynamics appear to be governed by different mechanisms in different frequency and flowrate regimes. These mechanisms were investigated using phase-locked, two- dimensional OH Planar laser-induced fluorescence imaging. From these images, two mechanisms, vortex rollup and unsteady flame liftoff, are identified as important in the saturation of the flame’s response to large velocity oscillations. Both mechanisms appear to reduce the flame’s area and thus its response at these high levels of driving.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Qualitative description of the dependence of acoustic driving, H(A), and damping, D(A), processes upon amplitude of oscillation, A

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Figure 2

Schematic of swirl-stabilized combustor

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Figure 3

Schematic of nozzle; all dimensions are in mm (not to scale)

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Figure 4

Schematic of laser setup for OH PLIF imaging

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Figure 5

Dependence of: (a)CH* oscillation amplitude; and (b)u′−CH*′ phase angle upon velocity oscillation amplitude (fdrive=210Hz, ϕ=0.80ReD=21,000). CH* saturation amplitude=0.45. Uncertainty in phase angle <5deg.

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Figure 6

Dependence of: (a)CH* oscillation amplitude; and (b)u′−CH*′ phase angle upon velocity oscillation amplitude, ϕ=0.80,ReD=21,000. CH* saturation amplitude ∼0.98. Uncertainty in phase angle <5deg.

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Figure 7

Dependence of CH* oscillation amplitude upon amplitude of velocity oscillations for two driving frequencies (ReD=21,000,ϕ=0.80)

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Figure 8

(a) Dependence of CH* oscillation amplitude upon amplitude of velocity oscillations for fdrive=160–180Hz; (b) dependence of u′−CH*′ phase angle upon velocity oscillation amplitude for fdrive=170Hz. (ReD=30,000, ϕ=0.80)

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Figure 9

Fourier transforms of: (a) pressure; and (b)CH* chemiluminescence signals at local maximum of transfer function and local minimum of transfer function for fdrive=180Hz(ReD=30,000,ϕ=0.80)

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Figure 10

Dependence of CH* nonlinear amplitude on driving frequency as a function of Reynolds number (ϕ=0.80)

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Figure 11

Phase-locked instantaneous line-of-sight images of flame over one cycle of acoustic forcing for: (a) low (linear, u′∕u0=0.2); and (b) high (nonlinear, u′∕u0=0.6) amplitude of oscillation (fdrive=410Hz, ReD=21,000, ϕ=0.80)

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Figure 12

Instantaneous OH PLIF images showing evolution of flame response over one cycle of acoustic forcing for: (a) low (linear, u′∕u0=0.3); and (b) high (nonlinear, u′∕u0=0.9) velocity oscillation amplitudes (fdrive=130Hz, ReD=21,000, ϕ=0.80)

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Figure 13

Averaged flame edges at 65–110deg phase angle at four velocity oscillation amplitudes (fdrive=130Hz, u′∕u0=0.3, 0.6, 0.83, and 0.90). Dashed (- - -)/ solid —) lines indicate peak flame response when transfer function is linear/saturated, respectively

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Figure 14

Instantaneous OH PLIF images showing evolution of flame response over one cycle of acoustic forcing for: (a) low (linear, u′∕u0=0.2); and (b) high (nonlinear, u′∕u0=0.6) velocity oscillation amplitudes (fdrive=410Hz, ReD=21,000, ϕ=0.80)

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Figure 15

Average flame edges at 180–225deg phase angle at four velocity oscillation amplitudes (fdrive=410Hz, u′∕u0=0.2, 0.3, 0.53, 0.6). Dashed (- - -)/solid (—) lines indicate peak flame response when transfer function is linear/saturated, respectively.

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