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Research Papers

Response Dynamics of Recirculation Structures in Coaxial Nonpremixed Swirl-Stabilized Flames Subjected to Acoustic Forcing

[+] Author and Article Information
Uyi Idahosa

GE Global Research Centre,
1 Research Circle,
Niskayuna, NY 12309

R. Santhosh, Ankur Miglani

Department of Mechanical Engineering,
Indian Institute of Science,
Bangalore 560 012, India

Saptarshi Basu

Department of Mechanical Engineering,
Indian Institute of Science,
Bangalore 560 012, India
e-mail: sbasu@mecheng.iisc.ernet.in

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received April 28, 2014; final manuscript received January 13, 2015; published online November 11, 2015. Assoc. Editor: Suman Chakraborty.

J. Thermal Sci. Eng. Appl 8(1), 011008 (Nov 11, 2015) (11 pages) Paper No: TSEA-14-1090; doi: 10.1115/1.4030728 History: Received April 28, 2014

This paper reports the time-mean and phase-locked response of nonreacting as well as reacting flow field in a coaxial swirling jet/flame (nonpremixed). Two distinct swirl intensities plus two different central pipe flow rates at each swirl setting are investigated. The maximum response is observed at the 105 Hz mode in the range of excitation frequencies (0–315 Hz). The flow/flame exhibited minimal response beyond 300 Hz. It is seen that the aspect ratio change of inner recirculation zone (IRZ) under nonreacting conditions (at responsive modes) manifests as a corresponding increase in the time-mean flame aspect ratio. This is corroborated by ∼25% decrease in the IRZ transverse width in both flame and cold flow states. In addition, 105 Hz excited states are found to shed high energy regions (eddies) asymmetrically when compared to dormant 315 Hz pulsing frequency. The kinetic energy (KE) of the flow field is subsequently reduced due to acoustic excitation and a corresponding increase (∼O (1)) in fluctuation intensity is witnessed. The lower swirl intensity case is found to be more responsive than the high swirl case as in the former flow state the resistance offered by IRZ to incoming acoustic perturbations is lower due to inherently low inertia. Next, the phase-locked analysis of flow and flame structure is employed to further investigate the phase dependence of flow/flame response. It is found that the asymmetric shifting of IRZ mainly results at 270 deg acoustic forcing. The 90 deg phase angle forcing is observed to convect the IRZ farther downstream in both swirl cases as compared to other phase angles. The present work aims primarily at providing a fluid dynamic view point to the observed nonpremixed flame response without considering the confinement effects.

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Figures

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Fig. 1

Isothermal velocity profiles using hot wire anemometry: (a) low swirl (S009) and (b) high swirl (S034)

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Fig. 2

Time-averaged isothermal streamlines—unpulsed (0 Hz) mode

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Fig. 3

Time-averaged CH* chemiluminescence images: (a) S009-C1, (b) S009-C2, (c) S034-C1, and (d) S034-C2 (partially adopted from Ref. [18])

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Fig. 4

Isothermal time-averaged streamlines for lean (C2) flow state: (a) S034-C2-0 Hz, (b) S034-C2-105 Hz, (c) S034-C2-315 Hz, (d) S009-C2-0 Hz (unpulsed), (e) S009-C2-105 Hz, and (f) S009-C2-315 Hz. (Reprinted with permission from Idahosa et al., 2010 [18].) The variations of dIRZ, yΔ, and yc with excitation frequencies are shown in (g), (h), and (i), respectively.

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Fig. 5

Frequency (time)-averaged isothermal fluid response—S009-C1: (a) unpulsed (α = 0.1), (b) 105 Hz forcing (α = 1), and (c) 315 Hz forcing (α = 1)

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Fig. 6

Frequency (time)-averaged isothermal fluid response—S034-C1: (a) unpulsed (α = 0.1), (b) 105 Hz forcing (α = 1), and (c) 315 Hz forcing (α = 1)

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Fig. 7

Phase-conditioned fluid dynamics—S009-C2-105 Hz: (a) 0 Hz, (b) ϕ = 90 deg, and (c) ϕ = 270 deg

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Fig. 8

Phase-conditioned fluid dynamics—S034-C2-105 Hz: (a) 0 Hz, (b) ϕ = 90 deg, and (c) ϕ = 270 deg

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Fig. 9

Phase-conditioned CH* chemiluminescence images. (Reprinted with permission from Ref. [18].)

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