Quote:
Originally Posted by freebeard
Not a brake, a spoiler.............
This lacks context, is it behind the endplate [not shown]?
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https://racer.com/2019/01/18/indycar...t-wing-tweaks/
On the other subject, the windshield rake.
I think of it as spoiler to lateral movement, as it creates a vortex for "reattachment", this a controlled disruption and not total havoc.
We are in another topic on the NASCAR pop out roof devises intended to interrupt lift, and not enhance it as with a Gurney Flap (
often in a downward direction).
Why Nascar uses roof flaps
https://www.carthrottle.com/post/wom7z7p/
Quote:
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These flaps are creating turbulence and creating a huge volume of slow, high pressure air on the side of the car on the opposite direction of the movement. This makes the car generate much less lift. This reduction is enough to prevent the car from flying over the security fences into the expectators.
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Talladega Teardown: Roof Flaps and Catch Fences
https://buildingspeed.org/blog/2009/04/26/roof_flaps/
Quote:
Roof flaps (the invention of which I detail in my book The Physics of NASCAR) are designed to keep cars on the ground. Faster-moving air exerts less pressure and slower-moving air exerts more pressure. A wing develops lift because the air flowing under the wing moves slower than the air going over the wing. That creates more pressure underneath the wing than over the wing, which generates a net force upward. You want that for an airplane, but you don’t want it for a race car.
A NASCAR race car is pretty stable when airflow comes from the nose to the tail. The problems start when the car turns sideways because a sideways racecar looks a little too much like a wing. Air flows over the roof of a sideways racecar very quickly. It stays attached to the car’s surface for a long time, and that creates a low pressure region on the top of the car. A little air (or another car) gets under the car and all of a sudden, the car is an airplane. This only happens when the car rotates enough, so you need a solution that only becomes active when the car is really yawed.
You want the air to detach from the car’s roof, which increases the pressure on the top of the car and decreases the lift. That’s where the roof flaps come in.
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Question is:
Are NASCAR roof flaps their own thing, or can they be called air brakes or glorified Gurney Flaps without misleading anyone?
Either way, I think NASCAR roof flaps do more than redirect the flow, they cause so much disruption, so much drag that the car stops being a wing when going sideways and or rolling, and of course the pressure differentials change - the author says this is the main reason they work - air pressure changes. They do not create down-force (
as in a vector change), they disrupt lift caused by clean attached air flow.
EDIT:
Gurney flap
https://en.wikipedia.org/wiki/Gurney_flap
Quote:
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The device operates by increasing pressure on the pressure side, decreasing pressure on the suction side, and helping the boundary layer flow stay attached all the way to the trailing edge on the suction side of the airfoil.[4]
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So, Gurney flaps accentuate existing air pressure differences, while Roof Flaps do the opposite in that they reduce the pressure differentials.
Now back to the windshield rake on the Indy car...............intended to maintain attachment via Gurney Flap vortex, or intended to disrupt the existing airflow around the windshield completely with no hope of reattachment?
I do not know the answer, but lean towards clean attached flow via Gurney Flap.
EDIT-2:
Found this, isolated car and when the car is near a wall - some weird pressure changes happen.
2015
http://www.arcindy.com/arc-inside-tr...s-testing.html