Formation and flame-induced suppression of the precessing vortex core in a swirl combustor: Experiments and linear stability analysis

By Kilian Oberleithner, Michael Stöhr, Seong Ho Im, C. Arndt, Adam Steinberg. 2015

240 citations recorded by the source corpus.

Abstract The precessing vortex core (PVC) is a coherent flow structure that is often encountered in swirling flows in gas turbine (GT) combustors. In some swirl combustors, it has been observed that a PVC is present under non-reacting conditions but disappears in the corresponding reacting cases. Since numerous studies have shown that a PVC has strong effects on the flame stabilization, it is desirable to understand the formation and suppression of PVCs in GT combustors. The present work experimentally studies the flow field in a GT model combustor at atmospheric pressure. Whereas all non-reacting conditions and detached M-shaped flames exhibit a PVC, the PVC is suppressed for attached V-shaped flames. A local linear stability analysis is then applied to the measured time-averaged velocity and density fields. For the cases where a PVC appeared in the experiment, the analysis shows a global hydrodynamic instability that manifests in a single-helical mode with its wavemaker located at the combustor inlet. The frequency of the global mode is in excellent agreement with the measured oscillation frequency and the growth rate is approximately zero, indicating the marginally stable limit-cycle. For the attached V-flame without PVC, strong radial density/temperature gradients are present at the inlet, which are shown to suppress the global instability. The interplay between the PVC and the flame is further investigated by considering a bi-stable case with intermittent transitions between V- and M-flame. The flame and flow transients are investigated experimentally via simultaneous highspeed PIV and OH-PLIF. The experiments reveal a sequence of events wherein the PVC forms prior to the transition of the flame shape. The results demonstrate the essential role of the PVC in the flame stabilization, and thereby the importance of a hydrodynamic stability analysis in the design of a swirl combustor.

Subfields: Computational Mechanics

View Paper: https://www.semanticscholar.org/paper/8f375dd16e39586dec1586fb1c8dfa94048b80d9

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In Computational Mechanics

Citations in the corpus

Coherent structures in a swirl injector at Re = 4800 by nonlinear simulations and linear global modes (2016, methodology): “The frequency selection in local stability analyses of injector flows seems somewhat more robust than in global stability analyses, in that local analysis around the mean flow with molecular viscosity gives quite accurate predictions of the frequency (Juniper 2012; Oberleithner et al. 2015).”
Development and evaluation of gappy-POD as a data reconstruction technique for noisy PIV measurements in gas turbine combustors (2016, methodology): “The combustor has been the subject of numerous previous studies (e.g. Meier et al (2007); Franzelli et al (2012); Dem et al (2015); Oberleithner et al (2015)) wherein the geometry is discussed in detail, and the data used here were previously described by Steinberg et al (2013) and Caux-Brisebois…”
Spectral proper orthogonal decomposition (2015, methodology): “To deal with this issue, we conducted a linear stability analysis of the underlying mean flow, following the procedure outlined by Oberleithner et al. (2015).”