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Title: Effect of azimuthal flow fluctuations on flow and flame dynamics of axisymmetric swirling flames

We report recent studies have clearly shown the important role of swirl fluctuations (or, more precisely, fluctuations in axial vorticity) in the response of premixed flames to flow oscillations. An important implication of this mechanism is that the axial location of the swirler plays a key role in the phase between the acoustic flow excitation source and the resulting axial vorticity fluctuation at the flame. Similar to the previously well recognized role of azimuthal vorticity fluctuations, these swirl fluctuations are vortical and convect at the mean flow velocity, unlike the acoustic flow fluctuations. However, there is a fundamental difference between axial and azimuthal vorticity disturbances in terms of the flow oscillations they induce on the flame. Specifically, azimuthal vorticity disturbances excite radial and axial flow disturbances, while axial vorticity oscillations, in general induce both radial and azimuthal flow fluctuations, but in the axisymmetric case, they only directly excite azimuthal flow fluctuations. The axial vorticity fluctuations do, however, indirectly excite axial and radial velocity fluctuations when the axial vortex tube is tilted off-axis, such as at locations of area expansion. This difference is significant because axisymmetric flames are disturbed only by the velocity component normal to it, which stem from axialmore » and radial velocity components only. This implies that axisymmetric mean flames are not directly affected by azimuthal flow fluctuations, since they are tangential to it. Thus, it is the extent to which the axial vorticity is tilted and rotated that controls the strength of the flow oscillations normal to the flame and, in turn, lead to heat release oscillations. This coupling process is not easily amenable to analytical calculations and, as such, we report here a computational study of the role of these different flow fluctuations on the flame response in an axisymmetric framework. In conclusion, the results indicate that the swirl fluctuations can act as significant source of flame heat release disturbances, due to azimuthal and radial vortex tubes tilting in mixing passage boundary layers and at the expansion into the combustor.« less
Authors:
 [1] ;  [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States). School of Aerospace Engineering
Publication Date:
Grant/Contract Number:
NT0005054
Type:
Accepted Manuscript
Journal Name:
Physics of Fluids
Additional Journal Information:
Journal Volume: 27; Journal Issue: 10; Journal ID: ISSN 1070-6631
Publisher:
American Institute of Physics (AIP)
Research Org:
Pennsylvania State Univ., University Park, PA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 42 ENGINEERING
OSTI Identifier:
1469562
Alternate Identifier(s):
OSTI ID: 1224328

Acharya, Vishal, and Lieuwen, Timothy. Effect of azimuthal flow fluctuations on flow and flame dynamics of axisymmetric swirling flames. United States: N. p., Web. doi:10.1063/1.4933135.
Acharya, Vishal, & Lieuwen, Timothy. Effect of azimuthal flow fluctuations on flow and flame dynamics of axisymmetric swirling flames. United States. doi:10.1063/1.4933135.
Acharya, Vishal, and Lieuwen, Timothy. 2015. "Effect of azimuthal flow fluctuations on flow and flame dynamics of axisymmetric swirling flames". United States. doi:10.1063/1.4933135. https://www.osti.gov/servlets/purl/1469562.
@article{osti_1469562,
title = {Effect of azimuthal flow fluctuations on flow and flame dynamics of axisymmetric swirling flames},
author = {Acharya, Vishal and Lieuwen, Timothy},
abstractNote = {We report recent studies have clearly shown the important role of swirl fluctuations (or, more precisely, fluctuations in axial vorticity) in the response of premixed flames to flow oscillations. An important implication of this mechanism is that the axial location of the swirler plays a key role in the phase between the acoustic flow excitation source and the resulting axial vorticity fluctuation at the flame. Similar to the previously well recognized role of azimuthal vorticity fluctuations, these swirl fluctuations are vortical and convect at the mean flow velocity, unlike the acoustic flow fluctuations. However, there is a fundamental difference between axial and azimuthal vorticity disturbances in terms of the flow oscillations they induce on the flame. Specifically, azimuthal vorticity disturbances excite radial and axial flow disturbances, while axial vorticity oscillations, in general induce both radial and azimuthal flow fluctuations, but in the axisymmetric case, they only directly excite azimuthal flow fluctuations. The axial vorticity fluctuations do, however, indirectly excite axial and radial velocity fluctuations when the axial vortex tube is tilted off-axis, such as at locations of area expansion. This difference is significant because axisymmetric flames are disturbed only by the velocity component normal to it, which stem from axial and radial velocity components only. This implies that axisymmetric mean flames are not directly affected by azimuthal flow fluctuations, since they are tangential to it. Thus, it is the extent to which the axial vorticity is tilted and rotated that controls the strength of the flow oscillations normal to the flame and, in turn, lead to heat release oscillations. This coupling process is not easily amenable to analytical calculations and, as such, we report here a computational study of the role of these different flow fluctuations on the flame response in an axisymmetric framework. In conclusion, the results indicate that the swirl fluctuations can act as significant source of flame heat release disturbances, due to azimuthal and radial vortex tubes tilting in mixing passage boundary layers and at the expansion into the combustor.},
doi = {10.1063/1.4933135},
journal = {Physics of Fluids},
number = 10,
volume = 27,
place = {United States},
year = {2015},
month = {10}
}