Quote:
Originally Posted by J-W
Quote:
Originally Posted by lamawithonel
I noticed these square-tooth wheel spats on a Maserati Ghibli the other day. Anybody know why they're like that? The only thing I can think is maybe something to do with noise, like the exhaust outlets of the 787.
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In simple terms, they allow a smoother separation for the air as it flows along the sides of the engine where turbulent air and smooth flowing are meet. 90° angles and perpendicular angles to air flow have typically higher drag. |
Yes and no. The jagged edge helps transition the hot, highly turbulent exhaust stream into the cool, relatively smooth air surrounding the engine. The major result is a reduction in exhaust noise. I imagine the reduced turbulence has some effect on drag, but small enough that it hasn't been mentioned in any of the Boeing literature. The picture is a link and has more details.
Anyway... The Gihbli picture somehow didn't make it in my original question, but that's what the question was about. Here it is again with the wheel spats highlighted and enlarged-- uploaded this time. I found the answer, though.
The serrated edge stabilizes shear waves, according to
this Mercedes CLA press release. That would reduce wind noise, though it's unclear if it that's a side-effect or the direct intent; the press release is about Cd. It also doesn't explain how it works exactly, but I'm curious to find out. Anybody with a CFD capability care to model these and test them on our platform to see? My best guess is that it creates countervailing waves that cancel each other out, but I'd love to see some real data.