Quote:
Originally Posted by niky
No, I mean, more like rails along the side to keep air from spilling over the side of the roof.
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The reason the air will want to spill over is that the air traveling over the top of the car travels a longer distance than that of the sides, and therefore will be of a different air pressure.
The higher pressure (slow air) at the sides will rise up to greet the lower pressure (fast air) and when doing so may create a vortex or funnel of rotating air.
The fences or rails at the edge of the roof line similar to a fender flare of a early 1970's McLaren race car will only delay the vortex formation, not eliminate it.
The delay might be useful in directing or locating the vortex to where you want it, perhaps you want it at another fin or wing for some reason - I don't know.
I wrote the above imagining a wind tunnel where the air is moving, because I have not yet come to terms with the air being still and the body moving through it. I'm pretty sure most people find the wind tunnel thinking favored over what ever the other method may be.
The #5 and #7 cars in the front are the Mclarens with fender fences.
Random TRANSPORTATION pictures - Page 1740 - Pelican Parts Technical BBS
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I suspect that you don't see this done very often because delaying the vortex does not always lessen drag.
