Quote:
Originally Posted by Cd
Aerohead, this is a question for you :
How would this Kach22i idea work out ? 
This is actually exactly what I had in mind by the fences.
Normally the air starts to spill over the sides and meets at the back of the car in one huge vortex. I would think that fences like the one illustrated by Kach22i would minimize the size of the vortex since the main air spilling over the cars roof would not mix with the spiraling air on either side of the car. |
Cd,I'll try 'n do your question justice.
*The fence itself does nothing to alter the tranverse pressure gradient which drives the higher pressure air from below and on the sides towards the backlight/boot area.
*The fence WOULD in effect,limit the air's open access up top,just as the capping plates do on racing spoilers,and winglets on aircarft wings.
*One risk,is that the backlight area may already 'optimized' by the manufacturer (as with the Dodge Charger Daytona) and the fin will destroy the C-Pillar flow onto the boot, which is part of the drag/lift equation and balance.
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On my CRX I extended the contour of the rear slope essentially with two-fences which followed the 'Template' ,however they were embedded within side fairings sculpted to match the C-pillars outer contour,blending the flow while gently boat-tailing in.
Spanning the 'fences' were an upper Kamm-wing extension over the glass to extend the roofline camber,directing the 'jump' towards a low wing spoiler below.It also provides some shade to the cabin.
This contraption sequestered a bird-bath if you will,of vorticity and dead air for the outer flow to 'jump,' while preventing any really weird CG/CP effects.The CRX is un-phased by gust or crosswind.
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By the time the air from below reaches up top,the upper flow has slowed and gained pressure to match the side flow,killing the attached vortices in their crib.
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Volkswagen's Lamborghini division is doing this today so they don't have to add crap to the car top kill rear lift.The basic shape of the rear is incapable of generating lift as it is generally understood.
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So George's idea has merit.But I would take it to the next level,fully sculpting them into the rear slope to help regain what is lost on the C-Pillars.Chevrolet Division has finally,after 60-years,killed the drag in this area of their Corvette,filling this area in.