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Old 04-08-2020, 06:21 PM   #41 (permalink)
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Makes sense, however I suspect any kinetic energy in the back window area, "shadow", is likely more turbulent if of any velocity. But depending on exact placement, it might even be opposite to the cars direction, and not sure I want to constantly explain why my NACA inlet brake ducts are backwards.

So I'll ponder that further.

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Old 04-10-2020, 11:08 AM   #42 (permalink)
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back window

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Originally Posted by j-c-c View Post
Makes sense, however I suspect any kinetic energy in the back window area, "shadow", is likely more turbulent if of any velocity. But depending on exact placement, it might even be opposite to the cars direction, and not sure I want to constantly explain why my NACA inlet brake ducts are backwards.

So I'll ponder that further.
Yeah,the backlight area is all turbulence.It's nothing but entropy,with no way to harvest any kinetic energy of the swirling eddies.There may be an area where central downwash crashes onto the top of the trunklid,which could 'push' air into a break cooling duct.Tufting would tell the tale.Volkswagen,Porsche,and other rear-engine cars have taken advantage of this effect to harvest engine cooling air.You'd be looking for a 'star' pattern in the tufts,radiating away from an apparent 'center.'
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Old 04-10-2020, 01:09 PM   #43 (permalink)
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Problem is as I see, locating a useful spot behind the back window would be akin to chasing one's tale, in that it likely would be very vehicle velocity dependent, ie constantly moving.

I was pondering fabbing a partial secondary simple plexiglass outer back window glass, with better aero slope, and drill a horizontal line of small brake inlet holes across that upper outer new window, and then suck brake air from that confined space between the two.

This makes me wonder, if by improving/lowering the air flow over the "new" back window, and also removing some turbulence, I might actually just increase lift in that area, that the wing will only be able to in best conditions only negate, instead of the real goal of adding DF.
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Old 04-10-2020, 01:35 PM   #44 (permalink)
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velocity-dependent

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Originally Posted by j-c-c View Post
Problem is as I see, locating a useful spot behind the back window would be akin to chasing one's tale, in that it likely would be very vehicle velocity dependent, ie constantly moving.

I was pondering fabbing a partial secondary simple plexiglass outer back window glass, with better aero slope, and drill a horizontal line of small brake inlet holes across that upper outer new window, and then suck brake air from that confined space between the two.

This makes me wonder, if by improving/lowering the air flow over the "new" back window, and also removing some turbulence, I might actually just increase lift in that area, that the wing will only be able to in best conditions only negate, instead of the real goal of adding DF.
From 20-mph,up to 250-mph the flow will be identical around the body.Tufting and observing above 20-mph WOULD reveal your flow,without variance.If that helps any.
General Motors actually did the backlight modification for NASCAR in the 1980s.After Ford did Thunderbird.
As to drilling perpendicular holes in the Plex for air,you'd be looking at the highest known drag inlet,with 'vena-contracta',separated-flow,pinched-flow resistance,and adding to the power required to pull the air in.
Any angle more than 23-degrees will produce full separation,however,reducing the angle increases the reattachment on the trunklid.The wing on the Dodge Charger Daytona cost Cd 0.01.

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