Velocity distributions close to the wingtip of the different configurations.

The graph above shows the local velocity on the surface of the wing, at the 99% span station. The upper set of lines represents the velocity on the upper surface, the curves falling more closely together are for the lower surface, which is of no interest here. Starting with the black line for the wing tip without winglets, we see that all winglet configurations raise the velocity on the upper surface, but at different places.

• The winglet with the smooth, large fairing (red line) shifts the velocity distribution to higher velocities, without a large distortion. Close to the trailing edge, the velocity must reach the value of the lower side, resulting in a steeper gradient there. This configuration is not increasing the stress on the boundary layer very much, but it has a relatively large surface and is more work to build.
• The winglet with the sharp corner (green) shows a quite distorted velocity distribution, with a suction peak close to the leading edge, which can lead to premature transition into turbulent flow. The following region up to 60% of the chord shows a flat pressure gradient, which favors laminar flow, bit it is followed by a steeper velocity drop towards the trailing edge, which increases the risk of flow separation.
• Moving this winglet downstream (blue) shows almost no change in the first 50% of the chord and the velocity distribution up to 80% of the chord is much flatter than the original airfoil. This can lead to a larger area of laminar flow. The pressure rise towards the tailing edge is not much steeper than that of the base airfoil, because the trailing edge velocity is also raised. The result will be similar to the well rounded fairing configuration, probably even better.

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