Quote:
Originally Posted by donee
The aircraft people use them further forward. On most commercial aircraft I have been on one can see the VG's just behind the thickest part of the wing. Yea, they are probably doing that to get them out of the 500 mph boundary layer, but just ahead of seperation at low speeds. The purpose in commercial aircraft is to provide a lower stall speed.
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It's in the right spirit, but it's really not applicable - the stall speed of a commercial aircraft is still too fast for any direct comparison to a car - not to mention, an airfoil is a streamlined body while a car is a bluff body
Quote:
Originally Posted by donee
For cars the flow is thrown upward at the wind screen. The boundary layer is tight and laminar just before it goes over the roof on the typical car (not a Prius), but then through momentum jumps well up above the roof.
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No, Metro touched on it - but here's a little more info as this isn't the first time I've noticed this assumption. IF we assumed that fluid only entered at the base of the hood, this would be correct - this is not the case, free stream flow enters at all points, including arbitrary distances up the windscreen and AT the boundary layer level of the roof. Flow impeded by the windscreen slightly stagnates - it has less momentum compared to the mass airflow from entering free stream fluid.
Even if the windscreen is near perpendicular, we don't see a huge diversion upwards. Instead, we see stagnation and recirculation - something like this.
Quote:
Originally Posted by donee
There is a thread on here which says Tubulence and Vorticity are good if they reduce the cross-section of the total disturbed air, ie the reduce effective vehicle cross section area. Otherwise, your just putting energy into wasteful flow.
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That may have been my thread.... If it was, I need to put more emphasis on how we're stabbing in the dark with respect to placement... There's little margin for error... It should also be mentioned, if it hasn't been already - items to perturb the flow (such as VG's) are band aids for poor aerodynamic design.