10 replies to this topic

[Antoine]

I know there 's a high pressure area ahead of the front wheel in motion and a low pressure behind and above
But I don't understand why the audi louver in Le Mans version are so backward, is there an internal pipe which pick the high pressure behind the wheel?
Or there is an air flow around the wheel in motion from front, above and backward by the louver (I don't think because the wheel turn in the opposite way of this air flow!)

Does someone have some information about gurney shark teeth? I want to test but we don't have a lot of test day before the next race...

What's your opinion?

[Antoine]

Audi in big louver configuration:


Audi in small louver configuration: LM 2004 test


The gain in drag is easy to see but what about the louver efficiency and the downforce reduction!

[Pioneer]

Could it be that the louver's purpose is not to exhaust high pressure air from the spinning wheel but in fact to exhaust heated air from the brake ducts?

[Monstrobolaxa]

Well I agree with pioneer....the idea might to extract hot air from the brakes and wheel bearing. due to the closed "enviorment" there isn't a whole lot of air going through this area....and the hot air would have a bad influence on the brakes, due to lack of cooling....another thing is that if the hot air isn't extracted it might heat up the inner wall of the tire.

[dosco]

Originally posted by Pioneer
Could it be that the louver's purpose is not to exhaust high pressure air from the spinning wheel but in fact to exhaust heated air from the brake ducts?

I doubt it. Usually on these types of cars, there is an "intake" on the front end (often it is just a "hole" on the leading edge of the front bodywork). My thought is that there is enough pressure using this type of arrangement to "blow" air though the connecting duct, through the wheel hub, and through the disc to provide cooling air.

The louvres may help "extract" air, but......a spinning wheel enclosed in tight-fitting bodywork acts as an "air pump" and can create a high pressure area inside the bodywork. By adding the louvres, the air has a place to "get out" of the bodywork. I'm sure at high speeds the airflow over the louvres also creates enough pressure difference to "suck" air out of the bodywork.....thus the reason the louvres face the aft end of the car.

Lastly, Antoine, you've asked for information regarding the serrated gurney flaps in 2 threads now. If there was more information available, you'd probably have heard about it by now.

Check desmos tech/PDF thread, and also check out scarb's website.

[swintex]

I seem to recall reading some time ago (in a book by Paul Frere??) about the aero development of the Porsche 917 that these louvres reduced front end lift quite dramatically, balancing the low pressure area above and behind the front wheelarch by drawing high pressure air from within the wheelarch.

Must try and find that book.

[onepablo]

No, the louvers are definitely not for brake cooling. As dosco pointed out, the high rotation speeds of the tire creates a high pressure area within the wheelarch, creating lift. Brake cooling us usually acomplished via ducts behind the front wheel:

http://www.mulsannes...om/rey02s-2.htm


The only mention I've found on serrated gurneys:

lhttp://www.mulsannescorner.com/panozlmp07-5.html

[Wuzak]

DTM cars have exit holes at the rear of the wheel well for exactly the same reason, and maybe louvres too (I can't recall if they do or not).

[Antoine]

For brake cooling, there is an intake under the "nose" you can see on the R8. This intake is just for that!
So no problem with brake cooling.

Dosco, swintex and onepablo are rigth, it's not for cooling but to reduce the hight pressure into the wheel arch!
But my question is to know if the pressure repartition is like an open wheel (hight pressure in front and low pressure above and behind) or if the wheel arch create a hight pressure all around the wheel!
It's very important to know where I have to put the louvers, in front or in rear or in rear but with louvers that pick the hight pressure in front with an air duct....

In fact even in aerodynamics book, it's difficult to find some informations about louvres!
Swintex if you have more info, I'm open!

[dosco]

Originally posted by Antoine
Dosco, swintex and onepablo are rigth, it's not for cooling but to reduce the hight pressure into the wheel arch!
But my question is to know if the pressure repartition is like an open wheel (hight pressure in front and low pressure above and behind) or if the wheel arch create a hight pressure all around the wheel!
It's very important to know where I have to put the louvers, in front or in rear or in rear but with louvers that pick the hight pressure in front with an air duct....

What is the wheel arch geometry?

How close is the wheel arch to the wheel?

What is the design condition that you want the louvres to work? Max speed, average speed? (I'd think max speed.....but sounds like you're the designer)

Where are you "allowed" to put the louvres?

Basically the problem is a boundary layer/viscosity interaction issue, which of course is highly dependent on geometry and reynold's number. The pressure field will not be the same as the open-wheel case, due to the wheel arch/bodywork enclosure. The interaction will exist between the inside of the wheel arch, the gap formed by the intersection of the bottom of the car and the wheel enclosure, and the wheel itself.

Need.....more....information....

[Antoine]

We need louvers work between 70 to 220 Km/h
We could take about 300Km/h in straight! so we need very low drag!


The wheel is not so close to the wheel arch about 5cm
The wheel arch geometry is straight vertical on front and concentric with the tire on the rear at about 5cm!

Do you want to try something on cfd? Because I can give you a good geometry plan of the wheel arch, if you want to test it in cfd or something like that...

About the regulation:"The louvers are mandatory above the front wheels without protuding more than 20mm. Total area of the openings: 25 sq in (160cm²) as a minimun on each side