Time-resolved blowoff transition measurements for two-dimensional bluff body-stabilized flames in vitiated flow |
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Authors: | Steven G Tuttle Swetaprovo Chaudhuri Stanislav Kostka Kristin M Kopp-Vaughan Trevor R Jensen Baki M Cetegen Michael W Renfro |
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Affiliation: | 1. Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, United States;2. Center for Turbulence Research, Stanford University, Stanford, CA 94305, United States;1. Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA;2. Department of Mechanical Engineering, Oakland University, Rochester, MI 48309, USA;1. Department of Energy Sciences, Lund University, PO Box 118, SE-221 00 Lund, Sweden;2. Department of Mechanical and Construction Engineering, Northumbria University, NE1 8ST Newcastle, UK |
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Abstract: | Flame holding and blowoff characteristics of bluff-body stabilized, turbulent flames were measured in an enclosed rectangular duct with a triangular flame holder in vitiated, premixed flows. Blowoff stability margins were characterized with chemiluminescence measurements performed by high-speed imaging to capture flame dynamics during the approach to flame blow off. As the equivalence ratio was decreased, local extinctions along the flames interacting with shear layers surrounding the bluff body recirculation zone occurred with greater frequency and proximity to the wake stagnation zone. Decreased equivalence ratio resulted in extinction events at the trailing edge of the stagnation zone, which allowed reactants to be convected into the recirculation zone and burned behind the bluff body. Increasing reactant dilution of the recirculation zone eventually resulted in flame lift-off or extinction of the flame in the neighboring shear layer. These near field shear layer flames convected to the wake stagnation zone, and were eventually quenched. Simultaneous particle imaging velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) measurements captured the flame edge location and aerodynamic behavior as blowoff was approached. Two-dimensional hydrodynamic stretch along the flame front and flow field vorticity maps were extracted from the combined PIV/OH PLIF data. The distribution of flame stretch shifted to greater values as the equivalence ratio decreased and is believed to be the cause of local flame extinction in the wake stagnation zone that starts the blowoff process. |
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