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

Further Characterization of the Disturbance Field in a Transversely Excited Swirl-Stabilized Flame

[+] Author and Article Information
Jacqueline O’Connor1

School of Aerospace Engineering,  Georgia Institute of Technology, 270 Ferst Drive, Atlanta, GA 30332-0150joconnor6@gatech.edu

Tim Lieuwen

School of Aerospace Engineering,  Georgia Institute of Technology, 270 Ferst Drive, Atlanta, GA 30332-0150

1

Corresponding author.

J. Eng. Gas Turbines Power 134(1), 011501 (Oct 28, 2011) (9 pages) doi:10.1115/1.4004186 History: Received April 27, 2011; Revised April 28, 2011; Published October 28, 2011; Online October 28, 2011

This paper describes an analysis of the unsteady flow field in swirl flames subjected to transverse acoustic waves. This work is motivated by transverse instabilities in annular gas turbine combustors, which are a continuing challenge for both power generation and aircraft applications. The unsteady flow field that disturbs the flame consists not only of the incident transverse acoustic wave, but also longitudinal acoustic fluctuations and vortical fluctuations associated with underlying hydrodynamic instabilities of the base flow. We show that the acoustic and vortical velocity fluctuations are of comparable magnitude. The superposition of these waves leads to strong interference patterns in the velocity field, a result of the significantly different wave propagation speeds and axial phase dependencies of these two disturbance sources. Vortical fluctuations originate from the convectively unstable shear layers and absolutely unstable swirling jet. We argue that the unsteady shear layer induced fluctuations are the most dynamically significant, as they are the primary source of flame fluctuations. We also suggest that vortical structures associated with vortex breakdown play an important role in controlling the time-averaged features of the central flow and flame spreading angle, but do not play an important role in disturbing the flame at low disturbance amplitudes. This result has important implications not only for our understanding of the velocity disturbance field in the flame region, but also for capturing important physics in future modeling efforts.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Velocity disturbance mechanisms present in a transversely forced flame

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Figure 2

Representation of the (a) “base” flow state and (b) the unsteady flow superimposed

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Figure 3

Time-averaged (a) axial velocity and (b) vorticity in nonreacting (top half) and reacting (bottom half) flow. Bulk velocity is Uo  = 10 m/s. Dotted lines represent nominal jet centers and shear layer paths.

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Figure 4

Notional picture of the flow field for a transversely forced swirling jet with (a) out-of-phase and (b) in-phase acoustic forcing. Coherent structures in the inner shear layer (ISL) and outer shear layer (OSL) travel downstream, bending the jet column as they pass.

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Figure 5

Normalized filtered velocity and vorticity field for (a) out-of-phase and (b) in-phase acoustic forcing for reacting flow at a bulk velocity of Uo  = 10 m/s and a forcing frequency of fo  = 400 Hz

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Figure 6

Instantaneous normalized velocity and vorticity fields for (a) out-of-phase and (b) in-phase acoustic forcing for reacting flow at a bulk velocity of Uo  = 10 m/s and a forcing frequency of fo  = 400 Hz

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Figure 7

Comparison of the normalized filtered velocity and vorticity field between nonreacting (top half) and reacting (bottom half) flows at a bulk velocity of Uo  = 10 m/s and a forcing frequency of fo  = 400 Hz out-of-phase

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Figure 8

Phase of vorticity along shear layers for (a) nonreacting and (b) reacting flow at a bulk velocity of Uo  = 10 m/s and a forcing frequency of fo  = 400 Hz out-of-phase

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Figure 9

Normalized amplitude of axial velocity fluctuations for (a) nonreacting and (b) reacting flow at the forcing frequency at a bulk velocity of Uo  = 10 m/s and a forcing frequency of fo  = 400 Hz out-of-phase

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Figure 10

Normalized amplitude of transverse velocity fluctuations for (a) nonreacting and (b) reacting flow at the forcing frequency at a bulk velocity of Uo  = 10 m/s and a forcing frequency of fo  = 400 Hz out-of-phase

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Figure 11

Normalized amplitude of vorticity fluctuations for (a) nonreacting and (b) reacting flow at the forcing frequency at a bulk velocity of Uo  = 10 m/s and a forcing frequency of fo  = 400 Hz out-of-phase

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Figure 12

Time-averaged vorticity in shear layers for the (a) nonreacting and (b) reacting cases at a bulk velocity of Uo  = 10 m/s and a forcing frequency of fo  = 400 Hz out-of-phase. Dotted lines indicate exponential curve fits to calculate decay rates with downstream distance.

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Figure 13

Comparison of transverse velocity fluctuation amplitude in left and right jet of the (a) nonreacting and (b) reacting data and the two-wave interaction fit. The bulk velocity was Uo  = 10 m/s and the forcing frequency was fo  = 400 Hz out-of-phase.

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