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Experimental Study of Transient Mechanisms of Bi-Stable Flame Shape Transitions in a Swirl Combustor

[+] Author Affiliations
Michael Stöhr, Zhiyao Yin, Wolfgang Meier

German Aerospace Center (DLR), Stuttgart, Germany

Kilian Oberleithner, Moritz Sieber

Technische Universität Berlin, Berlin, Germany

Paper No. GT2017-65003, pp. V04BT04A063; 11 pages
doi:10.1115/GT2017-65003
From:
  • ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition
  • Volume 4B: Combustion, Fuels and Emissions
  • Charlotte, North Carolina, USA, June 26–30, 2017
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-5085-5
  • Copyright © 2017 by ASME

abstract

Sudden changes of flame shape are an undesired, yet poorly understood feature of swirl combustors used in gas turbines. The present work studies flame shape transition mechanisms of a bistable turbulent swirl flame in a gas turbine model combustor, which alternates intermittently between an attached V-form and a lifted M-form. Time-resolved velocity fields and 2D flame structures were measured simultaneously using high-speed stereo-PIV and OH-PLIF at 10 kHz. The data analysis is performed using two novel methods that are well adapted to the study of transient flame shape transitions: Firstly, the linear stability analysis (LSA) of a time-varying mean flow and secondly the recently proposed spectral proper orthogonal decomposition (SPOD). The results show that the transitions are governed by two types of instability, namely a hydrodynamic instability in the form of a precessing vortex core (PVC) and a thermoacoustic (TA) instability. The LSA shows that the V-M transition implies the transient formation of a PVC as the result of a self-amplification process. The V-M transition, on the other hand, is induced by the appearance of a TA instability that suppresses the PVC and thereby modifies the flow field such that the flame re-attaches at the nozzle. In summary these results provide novel insights into the complex interactions of TA and hydrodynamic instabilities that govern the shape of turbulent swirl-stabilized flames.

Copyright © 2017 by ASME

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