Wind Energy

214 H. Guo et al.
and “b” in Fig. 38.2b at α =40◦ , which correspond to the minimum and
maximum lift, respectively. It can be observed from these pictures that:
1. The flow around the airfoil is dominated by alternately rolling up and
shedding of large vortices from leading and trailing edge. Laser sheet
visualization reveals the separated shear layer rolling up into smaller
vortices, smaller vortices amalgamating into a large vortex.
2. Maximum lift occurs when the large vortex just formed from the leading
edge and before its shedding downstream, as shown in Fig. 38.3b. The
area occupied by this vortex is characterized by higher negative vorticity.
When the minimum of the lift is reached, the large vortex evolves from
the trailing edge, as shown in Fig. 38.3a.
38.4 Conclusions
This experimental study revealed that the second maximum lift at α ≈ 40 ◦ is
induced by the large vortex developed from the amalgamation of the smaller
vortices from the leading edge.
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