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Impact of hydrogen addition on the thermoacoustic instability and precessing vortex core dynamics in a CH4/H2/air technically premixed combustor

Datta, A and Gupta, S and Hemchandra, S and Chterev, I and Boxx, I (2021) Impact of hydrogen addition on the thermoacoustic instability and precessing vortex core dynamics in a CH4/H2/air technically premixed combustor. In: ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition, GT 2021, 7-11 Jun 2021.

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Official URL: https://doi.org/10.1115/GT2021-58794

Abstract

We study the impact of H2enrichment on the unsteady flow dynamics and thermoacoustic instability in the single nozzle PRECCINSTA swirl combustor. We analyze data from two operating modes, premixed (PM) and technically premixed (TPM). The experiments were performed at atmospheric conditions with H2/CH4fuel mixtures at a global equivalence ratio of 0.65 while maintaining a constant thermal power of 20 kW. We examine the effect of H2addition on the flow dynamics by analyzing cases with three fuel compositions: 0 H2; 20 H2and 50 H2in both operating modes. A new multi resolution modal decomposition method, using a combination of wavelet transforms and proper orthogonal decomposition (WPOD) of the experimental time resolved high speed flow velocity and OH-PLIF measurements is performed. Thermoacoustic oscillations are observed in the TPM operating mode alone. WPOD results for the 0 H2TPM operating mode case reveals intermittent helical PVC oscillations along with axi-symmetric hydrodynamic flow oscillations due to the thermoacoustic oscillation. These oscillations cause local flame extinction near the nozzle centrebody resulting in liftoff. A precessing vortex core (PVC) oscillation develops in the flow that enables intermittent flame reattachment and results in intermittent thermoacoustic oscillations in this case. In the 0 H2PM case, the flame remains lifted off of the centrebody despite the presence of PVC oscillations in this case as well. H2enrichment results in the suppression of flame lift-off and the PVC in both operating modes. We show from flow strain rate statistics and extinction strain rate calculations that the increase of the latter with H2addition, allows the flame to stabilize in the region near the centrebody where the pure CH4cases show lift off. The lack of thermoacoustic oscillations in the PM operating mode shows that the primary heat release driving mechanism is due to fuel-air ratio oscillation that the thermoacoustic oscillation generates. The time averaged flow fields and the emergence of the PVC when the flame is lifted off, together suggest that PVC oscillations are caused by the separation between the vortex breakdown bubble and the wake behind the centrebody, as suggested by prior computational studies. © 2021 American Society of Mechanical Engineers (ASME). All rights reserved.

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 American Society of Mechanical Engineers (ASME)
Keywords: Combustors; Flow velocity; Hydrogen; Nozzles; Oscillating flow; Plasma oscillations; Principal component analysis; Strain rate; Thermoacoustics; Wavelet decomposition, CH 4; Core dynamics; Flow dynamics; Hydrogen addition; Operating modes; Precessing vortex core; Premixed; Thermoacoustic instability; Thermoacoustic oscillations; Wavelets transform, Vortex flow
Department/Centre: Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited: 28 Nov 2021 10:18
Last Modified: 28 Nov 2021 10:18
URI: http://eprints.iisc.ac.in/id/eprint/70315

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