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The role of the centerbody wake on the precessing vortex core dynamics of a swirl nozzle

Mukherjee, A and Muthichur, N and More, C and Gupta, S and Hemchandra, S (2020) The role of the centerbody wake on the precessing vortex core dynamics of a swirl nozzle. In: ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition, GT 2020, 21-25 Sept 2020, Virtual, Online.

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Official URL: https://dx.doi.org/10.1115/GT2020-15777


The precessing vortex core (PVC) phenomenon in swirling jets is a helical instability in the flow driven by the coherent precession of the vortex breakdown bubble (VBB) around the flow axis, resulting in the helical rollup of the shear layer. This instability is driven mainly by flow processes in the region upstream of the VBB. Centerbodies, commonly employed in combustor nozzles create a central wake recirculation zone (CWRZ) that can interfere with VBB precession and hence suppress the PVC. We study this phenomenon in a swirl nozzle with a centerbody whose end face is flush with the nozzle exit plane, using large eddy simulations (LES) and linear hydrodynamic stability analysis for flow Reynolds numbers Re = 48, 767 and 82,751, based on nozzle exit diameter and bulk flow velocity. For one of the Re = 82, 751 cases the centerbody end face diameter is halved resulting in the onset of coherent VBB precession. Linear stability analysis reveals a marginally unstable mode in this case. The same mode is found to be stable in the nominal cases. Structural sensitivity analysis for these two cases, shows that the VBB precession eigenmode is sensitive to changes in the time averaged flow in the VBB-CWRZ merger region. This suggests that the reduction in CWRZ length due to halving the centerbody end face diameter is the reason for the onset of VBB precession. These results suggest that in general, spatial separation between the CWRZ and VBB can result in the onset of VBB precession and the emergence of PVC oscillations in swirl flows. © 2020 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 of this article belongs to American Society of Mechanical Engineers (ASME)
Keywords: Flow velocity; Large eddy simulation; Linear stability analysis; Nozzles; Reynolds equation; Reynolds number; Sensitivity analysis; Turbomachinery; Vortex flow; Vorticity; Wakes, Helical instability; Linear hydrodynamics; Nozzle exit plane; Precessing vortex core; Recirculation zones; Spatial separation; Structural sensitivity; Time-averaged flow, Shear flow
Department/Centre: Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited: 25 Feb 2021 05:48
Last Modified: 25 Feb 2021 05:48
URI: http://eprints.iisc.ac.in/id/eprint/67984

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