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Originally Posted by trebuchet03
I doubt the submerged NACA thing is really it... But on the subject of s. NACA's - if they're shedding, they're improperly used/designed... The flow exiting the duct should be sufficient enough to prevent that from happening.... At least, that's what the research we've been doing has said... That, plus shedding makes noise :/
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I do agree the NACA roof channel argument is almost certainly wrong, it was just the first thing that came to mind.
As far as the vortex shedding, I first heard about it from a SportAviation (EAA magazine) article. The article reads:
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Originally Posted by SportAviation
A key and distinguishing feature of the NACA inlet is the curved profile's sharp edges. A common misconception is that the shape functions as a diffuser, but it does not. The edges shed vortices, which entrain air from the free stream flow and deposit it in the inlet.
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A figure is given showing vortices that looks like it is from a NACA report (the other figures are clearly ripped from NACA reports). I haven't been able to find the particular report, though. I have no idea whether the author is an aeronautical engineer or just an interested third party like me.
I suppose this could easily be solved with a little tuft testing...
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Originally Posted by trebuchet03
As for the roof line ridges.... One really can't ignore the structural advantages.... The geometry is stronger - so a thinner/lighter material can be used... That on top of aero benefits. Furthermore, flow over the center will be faster than flow over the sides due to interference/spillage over the side of the car.
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Interesting take on the interference idea.
It seems like designers killed a swarm of birds with one stone: decreased frontal area, increased structural stiffness, improved(?) style, + extra advantages (decreased interference drag).
Now the question is how much drag reduction does that feature net? 0.5%, 2%? I wonder...
- LostCause