Quote:
Originally Posted by rumdog
Ok thanks aerohead, very interesting indeed. I have often wondered about the shape of the 'cut'... and its influence on the eddies behind it.
i drew a little sketch, then read your post again... "no angles in the shape..." sort of answers my questions. So a continuous lip would be similar? - like the mercedes low drag concept?
then treat the rear surface with a porous material?
Man i want some windtunnel time! Thanks for the input.
oh one more thing, when you say ring vorticies, does that describe the eddies in the smoke tail? Or something else?
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*the lip on the Cd 0.19 Mercedes probably satisfies Morelli's conditions.
*the flow is streamlined (velocities and pressures similar)as it approaches the separation line.
*the separation line is perfectly transverse to the flow direction.
*the separation line is at,or very close to the trailing edge/lip.
*when viewed from the rear,the lip is elliptical in shape.
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As to the ring vortex itself,Morelli is not specific in this short (11-page) paper.
In NACA's (NASA) papers on airships,some of the aft-bodies were intentionally blunted.As the 'ring' of turbulent boundary layer sloughed off the rear of the airship hull,it filled in some of the void behind the blunt tail,to create a more streamlined phantom (or what Morelli is calling a 'fluid') tail,
made of this turbulence.
On the Mitsubishi Evo Lancer,the boundary layer thickness where the VGs were attached was up to 25mm thick.On our pickups it would be thicker because of their greater length,and this would be spilling into the wake.
There is also a jet pumping action which can take place behind truncated boat-tailed bodies which Morelli may be inferring.
With a healthy diffuser,this phenomena would be more likely to occur on a road vehicle.
Wheel fairings would make it even more likely.