A combination of postprocessing tools of OH*-chemiluminescence snapshots is used to characterize the coherent structures oftwo types of premixed burners: a bluffbody and an industrial swirl burner. Two methods are combined to extract the structures: a phase-averaging algorithm and the proper orthogonal decomposition. The first method is based on the estimation of the instantaneous phase of the snapshots relative to a (local) time-resolved signal. A phase-sorting- phase-averaging algorithm then reconstructs the evolution of the flame at a chosen frequency over one cycle. The proper orthogonal decomposition method is used as a filter to smoothen the snapshots. Both methods provide insight into the physical mechanisms of coherent structures in the two premixed flames under consideration. The snapshots of the bluff-body combustion exhibit a symmetric structure. This indicates that the von Kärmän vortex street in the cold flow is suppressed by the addition of heat in the shear layer. Three coexisting flame structures of the swirl burner in the combustion chamber could be identified: a natural helical structure of the burner and two axisymmetric modes. Increasing the amplitude of acoustic forcing at the natural flow frequency changes the helical structure to an axisymmetric one.
Combination of image postprocessing tools to identify coherent structures of premixed flames
Kombination von Bild-Nachverarbeitungstools zur Identifizierung kohärenter Strukturen vorgemischter Flammen
AIAA Journal ; 48 , 8 ; 1708-1720
2010
13 Seiten, 34 Bilder, 33 Quellen
Article (Journal)
English
Combination of Image Postprocessing Tools to Identify Coherent Structures of Premixed Flames
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