Scanning PIV investigation of the laminar separation bubble on a SD7003 airfoil |
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Authors: | Wei Zhang Rainer Hain Christian J Kähler |
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Institution: | 1. Institut für Str?mungsmechanik, Technische Universit?t Braunschweig, Bienroder Weg 3, 38106, Braunschweig, Germany 2. Department of Aerospace Engineering, Iowa State University, Ames, IA, 50014, USA 4. Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Institut für Aerodynamik und Str?mungstechnik, Lilienthalplatz 7, 38108, Braunschweig, Germany 6. Institut für Str?mungsmechanik und Aerodynamik, Universit?t der Bundeswehr München, Werner-Heisenberg-Weg 39, 85577, Neubiberg, Germany
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Abstract: | A laminar separation bubble occurs on the suction side of the SD7003 airfoil at an angle of attack α = 4–8° and a low Reynolds
number less than 100,000, which brings about a significant adverse aerodynamic effect. The spatial and temporal structure
of the laminar separation bubble was studied using the scanning PIV method at α = 4° and Re = 60,000 and 20,000. Of particular interest are the dynamic vortex behavior in transition process and the subsequent vortex
evolution in the turbulent boundary layer. The flow was continuously sampled in a stack of parallel illuminated planes from
two orthogonal views with a frequency of hundreds Hz, and PIV cross-correlation was performed to obtain the 2D velocity field
in each plane. Results of both the single-sliced and the volumetric presentations of the laminar separation bubble reveal
vortex shedding in transition near the reattachment region at Re = 60,000. In a relatively long distance vortices characterized by paired wall-normal vorticity packets retain their identities
in the reattached turbulent boundary layer, though vortices interact through tearing, stretching and tilting. Compared with
the restricted LSB at Re = 60,000, the flow at Re = 20,000 presents an earlier separation and a significantly increased reversed flow region followed by “huge” vortical structures. |
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