Abstract
Measurements of a laminar separation bubble on an NACA4412 airfoil were performed using volumetric three-component velocimetry (V3V) at a Reynolds number of 50,000 and different angles of attack. The time-averaged V3V results were analyzed to estimate the locations of transition onset and reattachment by interpreting the relationships of the different Reynolds normal and shear stresses to these locations. More specifically, the locations of separation and mean reattachment are defined as the beginning and end of the reverse-flow region, respectively. The onset of transition is located by finding the point where the growth rates of the Reynolds shear stresses changes significantly. The results show that the spanwise Reynolds normal stresses and the Reynolds shear stresses grow in the transition and reattachment regions, respectively, suggesting that three-dimensional disturbances grow before the complete breakdown to turbulence. Counter-rotating streamwise and wall-normal vorticity exist in the reattachment region. Organized relations are found between the streamwise vorticity, vortex cores, and ejection and sweep events.
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