A laminar separation bubble occurs on the suction side of the SD7003 airfoil at an angle of attack alpha = 4-8 deg and low Reynolds numbers less than 100,000, which brings about significant adverse aerodynamic effect. The spatial and temporal structure of the laminar separation bubble was studied by using a scanning PIV method at alpha = 4 deg 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 hundred 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 remain their identities in the reattached turbulent boundary layer, though vortices interact through tearing, stretching and tilting. Compared with the restricted LSB (Laminar Separation Bubble) at Re=60,000, the flow at Re=20,000 presents an early separation and a significantly increased reversed flow region followed by 'huge' vortical structures.
Scanning PIV investigation of the laminar separation bubble on an SD7003 airfoil
Raster-PIV-Untersuchung der laminaren Ablösungsblase an einem Flügelprofil SD7003
2007
19 Seiten, 18 Bilder, 2 Tabellen, 26 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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