Engine Compartment Venting

[jime57]

Originally Posted by arcosine

I don't know why the square back and notch back are so different, very strange. The blue defiantly had more air flowing, because of the bigger opening.

If you take a look at the colored pressure planes behind the cars, I think there may be a clue. The dark blue area, the lowest pressure area, on the notchback is much smaller than on the squareback. It looks to me like the notchback configuration is just barely good enough to see reattachment of the rear flow at the slightly extended trunk surface. That would make the dead air area smaller for the notchback. Scroll down to the point that the color planes for the notchback and the squareback are both visible, one above the other, and you will see the difference. There's lots of information in this paper and it takes a while for it to sink in.

I don't think this paper applies completely.............

They rarely do because the researchers must draw the constrains narrow enough to get it done in the allocated wind tunnel time. Even here, they ran out of time. They just can't cover the general cases. Even Hucho, when he practically owned the VW wind tunnel in the 70' and 80's, had to deal with budget constraints, and production schedules, which limited his use. Takes lots of money to turn on those big fans, even when you own them

[arcosine]

Sorry, but show me one on an airplane that's mounted backwards..

Its hard to believe that a notchback will suck that much more air out of the front wheel well. Maybe the notchback has lower overall drag and thus the open wheel well adds a proportionally larger amount.

[ConnClark]

Originally Posted by arcosine

Sorry, but show me one on an airplane that's mounted backwards..

Its hard to believe that a notchback will suck that much more air out of the front wheel well. Maybe the notchback has lower overall drag and thus the open wheel well adds a proportionally larger amount.

Cd of notchback with out moving ground simulation = 0.286
Cd of Notchback with moving ground simulation = 0.277

Cd of SquareBack/Estate with out moving ground simulation = 0.318
Cd of SquareBack/Estate with moving ground simulation = 0.319

http://delphi.com/pdf/techpapers/2012-01-0168.pdf

[radioranger]

Cobra daytona coupe or ford GT both with hood venting and pretty darn fast daytona coupe was reported going over 190 on the british M1 highway i think they called it and reportedly was the reason the road got a speed limit! so if you can pick up almost 30 mph with the same engine combo , the aero cant be that bad,

[jime57]

Originally Posted by ConnClark

Cd of notchback with out moving ground simulation = 0.286
Cd of Notchback with moving ground simulation = 0.277

Cd of SquareBack/Estate with out moving ground simulation = 0.318
Cd of SquareBack/Estate with moving ground simulation = 0.319

http://delphi.com/pdf/techpapers/2012-01-0168.pdf

But wasn't this primarily due to the different configurations at the rear of the two vehicles, and the amount of wake they created. The differences due to the ventioning of cooling air were minor by comparison. Did I miss something?

[jime57]

Originally Posted by radioranger

Cobra daytona coupe or ford GT both with hood venting and pretty darn fast daytona coupe was reported going over 190 on the british M1 highway i think they called it and reportedly was the reason the road got a speed limit! so if you can pick up almost 30 mph with the same engine combo , the aero cant be that bad,

According to Hucho's text reference to the research of Buchhein, et. al., the over hood venting is far and away better than any other venting. It is widely used on race cars, but isn't very practical for street cars, since it dumps lots of hot air right into the climate control intake at the windshield base. But the delta Cd is .010 better than underneath or wheelwells.

The no compromise Lotus Elise uses top venting. Not sure where they pick up their cabin air intake.

I've toyed with trying the arrangement on my "test" Insight. I think I see a way to get clean cabin air through the fenders with NACA ducts. Big project and not sure when/if it gets done.

[arcosine]

http://ecomodder.com/forum/showthrea...-15529-16.html

[aerohead]

If you can locate a copy of Paul Van Valkenburgh's book,Race Car Engineering. He has a section on measuring pressures on the outside of a cars body which would be invaluable,short of a wind tunnel,for siting cooling system exits.
For a 'clean-sheet' race car design you could slect one of the off-the-shelf designs depicted by Hucho or Korff.For a production vehicle you're going to be challenged because of the existing underhood architecture.
Professor Alberto Morelli probably spent millions of dollars perfecting the outlets on the CNR 'banana' car of 1978.
You could not have chosen a more difficult project to take on.
This is truly a case-specific-basis only type proposition.With the variety of vehicles out there,there won't be any one-size-fits-all solution.

[freebeard]

the over hood venting is far and away better than any other venting. It is widely used on race cars, but isn't very practical for street cars, since it dumps lots of hot air right into the climate control intake at the windshield base.

I can't find a good illustration of where the Saturn ventilator opening are; but maybe this could help. A generic fiberglass hood scoop that feeds into a spoiler in front of the wipers. If the opening was mid-hood, tall and narrow with a low, wide exit and your exhaust vents were in the back corners of the hood... Just crazy enough that it might work?

[wungun]

My RS front bumper on my Focus uses these functional vents..



There is baffles behind the rad to help duct out the air towards these side vents...