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I seem to recall a sailplane study of ZigZag tape, testing for the optimum zigzag angle. Seems like it was ~60 degrees, but I'm not sure. This stuff was on the vertical fin of a Stemme S-10 motorglider that I looked at, and was about ~0.30" thick. Got better control authority because the rudder was operating in cleaner air closer to the skin, making the rudder more effective and efficient.
Maybe the way these things work is that each zig makes its own little vortex, which rotates CW or CCW. Anyhow, the down side of the rotation of one zig flow meets the up side of rotation of the next zig flow, and they conflict and cancel each other out to some extent.
That's the theory behind why owl feathers are quiet, and why NASA et al are developing serrated trailing edges on the new generation of jet engine exhaust nozzles. Also, makes for better mixing of exhaust columns for less shear between axial flow rings, so less noise.
I hate car or other wind noise, so wanna try zigzag tape on the A pillar of my Bimmer. The inner sides of the mirrors already have little pimples as quietening turbulators, so some zigzag tape on the A pillar won't hurt.
Might put some ZZ tape just in front of the edges of the visora on my motorcycle helmets, to see of it lessens gap noise, which would be a big relief.
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