Quote:
Originally Posted by euromodder
I'm still hoping to hear how they differ from VGs ... well, not really.
They're too streamlined to do much IMO.
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A simple semi spherical bump is all that is needed to mix the slower boundary layer with the faster moving air above it. Before it goes over the bump the slower boundary layer only has faster moving air above it to help move it along. When the boundary layer is on top of the bump it has faster moving air on the top and sides. This faster moving air then will accelerate the boundary layer by transferring some of its energy to the boundary layer. Once the now faster moving boundary layer decends down the back side of the bump it merges with other slow air in the boundary layer and helps accelerate it.
A dimple on a golf ball works kind of the same way except sucks some of the faster moving air down to accelerate the slower air around the dimple.
The following report describes boundary layer control using all sorts of techniques. Included are VGs, Arches, Cylindrical posts, and many more. Its a good read if you have the time.
http://ntrs.nasa.gov/archive/nasa/ca...1994028565.pdf