EFFECT OF TRANSVERSE ACOUSTIC EXCITATION OVER A PARTIALLY-PREMIXED SWIRLING FLAME

Gupta, R and Bohrey, A and Panda, P (2024) EFFECT OF TRANSVERSE ACOUSTIC EXCITATION OVER A PARTIALLY-PREMIXED SWIRLING FLAME. In: 69th ASME Turbo Expo 2024: Turbomachinery Technical Conference and Exposition, GT 2024, 24 June 2024 through 28 June 2024, London.

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Abstract

In this work, we investigate the effect of transverse acoustic excitation on a partially premixed swirling flame. Azimuthal instabilities in annular gas turbine combustors are one of the major challenges. Thermoacoustic instabilities are driven by azimuthal acoustic modes. We have designed and fabricated a multi-nozzle linear array combustor to simulate the flow conditions of an annular combustor. The nozzle features an axial swirler with a centerbody acting as a fuel injector. Simultaneous high-speed chemiluminescence (OH�) and high-frequency pressure measurements are conducted to measure the time-averaged flame shape and the chamber acoustics respectively. These measurements are taken at multiple forcing frequencies and amplitude under in-phase (IP) and out-of-phase (OP) conditions. It is observed that, at one of the combustor modes (580Hz), during OP forcing, the flame transitions from a V-shape to an M-shape as the forcing amplitude is increased. However, with IP forcing the flame continues to remain in V-shape with the increase in forcing amplitude. Spectral proper orthogonal decomposition (SPOD) analysis of OH� images show that for OP forcing dominant mode shapes are present mostly at 0.5D away from the center-line, but for IP forcing the dominant mode shapes indicate combined axial and radial oscillations in the OH� intensity field. Furthermore, cross-wavelet transform (XWT) analysis shows a strong correlation between pressure fluctuations and OH� fluctuations around the forcing frequency for IP forcing, and a weak or intermittent correlation for OP forcing. Based on the acoustic simulation, instantaneous time snapshots of OH* chemiluminescence and existing literature, we hypothesize that the transition from V-shape to M-shape can be due to acoustically induced velocity and vortical fluctuations near burner lip during OP forcing. This causes the V-flame to stretch, roll outward, and stabilize in the outer recirculation zone (ORZ). Copyright © 2024 by ASME.

Item Type:	Conference Paper
Publication:	Proceedings of the ASME Turbo Expo
Publisher:	American Society of Mechanical Engineers (ASME)
Additional Information:	The copyright for this article belongs to the publishers.
Keywords:	Aerodynamics; Computational fluid dynamics; Gas turbines; Nozzles; Premixed flames; Pressure measurement; Swirling flow; Vortex flow; Vorticity; Wavelet decomposition, Acoustic excitation; Acoustic forcing; Forcing amplitudes; Forcings; In-phase forcing; OH chemiluminescence; Out of phase; Reacting swirling flow; Transverse acoustic forcing; V-shape, Combustors
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited:	06 Nov 2024 17:43
Last Modified:	06 Nov 2024 17:43
URI:	http://eprints.iisc.ac.in/id/eprint/86730

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