TY - GEN T1 - Investigation of the Global Mode in Swirling Combustor Flows: Experimental Observations and Local and Global Stability Analysis AU - Terhaar, Steffen AU - Paredes, P. AU - Oberleithner, Kilian AU - Theofilis, V. AU - Paschereit, Christian Oliver DO - 10.14279/DEPOSITONCE-6810 UR - https://depositonce.tu-berlin.de//handle/11303/7620 AB - Self-excited helical flow oscillations are frequently observed in gas turbine combustors. In the present work a new approach is presented tackling this phenomenon with stability concepts. Three reacting swirling flows are investigated. All of them undergo vortex breakdown, but only two of them show self-excited global flow oscillations at well-defined frequencies. The oscillations feature a precession of the vortex core and synchronized Kelvin-Helmholtz instabilities in the shear layers. Based on the mean flow fields, local and global linear hydrodynamic stability analyses are carried out. The dampening effect of the Reynolds stresses is accounted for by an eddy viscosity estimated from the experimental results. Both the local and the global analysis successfully identify linear global modes as being responsible for the large-scale flow oscillations and successfully predict their frequency. However, only the global analysis accurately predicts a globally stable flow field for the case without the oscillation, while the local analysis overpredicts the global growth rate. The predicted spatial distribution of the amplitude functions agree very well to the experimentally identified global mode. This successful application of global and local stability concepts to a complex and practically relevant flow configuration paves the way for the application of theoretically-founded passive and active control strategies. KW - 530 Physik KW - turbulent swirling flow KW - global mode KW - local and global stability analysis KW - eddy viscosity PY - 2015 PB - Technische Universität Berlin ER -