Rear Wing Fences

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Post Wed Apr 18, 2012 12:52 pm

[quote="Crucial_Xtreme"]

Think about why vorticies are present in this area: high pressure above the wing, low pressure beneath it & ambient pressure on the side of the endplate. What happens when these three meet? The high pressure flow naturally moves towards the low pressure area. This sets up a tumbling motion and a vortex is created.
/quote]

Image

if the endplate is short, vortex mergin occurs as shown...this simulation was done ona full 3d mesh...not a symmetry plane...i have a few flow viz at different yaw angles as well if anyone is keen...
n_anirudh
 
Joined: 25 Jul 2008

Post Wed Apr 18, 2012 5:13 pm

Crucial_Xtreme wrote:
Image


The statement associated with the right illustration, is it completely true? I can see where the louvers reduce the size of the vortex (drag), but in fact, does reducing the size of vortices equate to more downforce?

Brian
hardingfv32
 
Joined: 3 Apr 2011

Post Wed Apr 18, 2012 6:13 pm

With the endplates as they are on right, spillage should not be occuring in any significant amount until behind the wing. Reducing the size of the vortexes would imply that the pressure difference between the bottom and upper side is less. All else equal, this implies less downforce.

The louvres increase aero efficiency (ie. less drag for the same downforce), which the illustration states as "lessens drag and increases downforce", which isn't entirely accurate. The louvres probably reduce downforce as they bleed away the high pressure region above the wing.
Lycoming
 
Joined: 25 Aug 2011

Post Wed May 02, 2012 10:35 pm

hardingfv32 wrote:Note how the pressure actually looks lower near the end plates. I question the commonly given reason for the endplate louvers.

Brian

Image
By hardingfv32 at 2012-03-26


Hey wow, small world. I wrote that paper. That wing is currently (today I think) getting tested in germany for road legal certification (autoban speeds). I think that image was a low iteration count meant for pretty pictures and protecting IP. Of course we did sweeps at all the flap angles. Stall is around 45 IIRC, main plane is fixed.

At any rate, the bottom side the pressure is higher as you move outboard (lower is preferred). People do canted spans to improve this when you are rules limited to the total surface area of the wing, like we are in ACO GT classes, it also reduces pitch sensitivity. The idea is the more efficiently you use every square cm the less induced drag. I cant remember what formula is used to explain it now. I have my opinions on this, my colleagues have different ones

Slotted and relieved end plates can be a lot of things. But to me, the simple way to explain is that you push the tip vortices around trying to get better values. Thats the biggest thing I see change with stuff like that... the size, shape, location and intensity of the tip vortices. To be honest sometimes I dont really understand why everything is happening and I spend more time on that than most aerodynamicists I know. A lot of people just try to throw more tests at it until they get one that performs better.
gixxer_drew
 
Joined: 31 Jul 2010
Location: Yokohama, Japan

Post Thu May 03, 2012 1:15 am

hardingfv32 wrote:
The statement associated with the right illustration, is it completely true? I can see where the louvers reduce the size of the vortex (drag), but in fact, does reducing the size of vortices equate to more downforce?

Brian

By making a given wing set up more efficient (less drag for the downforce produced (a better L/D)) you can run more wing and thus gain downforce. Improved L/D means better d/f or less drag (or something in between). I think this is what they mean although they appear to be conflating the two issues.
Just_a_fan
 
Joined: 31 Jan 2010

Post Thu May 03, 2012 5:49 pm

The louver theme is getting extreme. Why bother with with the end plate above the main element? Is it requiered by the rules?

Why doesn't the end plate seal the bottom of the second element/flap? I though that an end plate on the low pressure side of a wing was always a benefit.

Brian

Image
hardingfv32
 
Joined: 3 Apr 2011

Post Fri May 11, 2012 3:58 am

hardingfv32 wrote:The louver theme is getting extreme. Why bother with with the end plate above the main element? Is it requiered by the rules?

Why doesn't the end plate seal the bottom of the second element/flap? I though that an end plate on the low pressure side of a wing was always a benefit.

Brian

[img]http://www.formula1.com/wi/sutton/2012/dms1203my25.jpg[img]



This is probably way too much information and sort of rantish but I dont get out much LOL. If I ever try to enjoy musings about aero junk... nobody has a clue what I'm talking about. I thought this might be a fun place to try. My senpai just says "dunno, gotta test it" and thats no fun is it?

You've got a high and low pressure side of the wing. So the formation of a large vortex is going to happen sooner or later. The end plate to me is about tuning the shape and size of the vortex to get the most desirable interaction with the wing. I can sometimes get that with a short, tall, long wide, thick or trapezoidal or whatever shape. My guess is that they are shedding a vortex or a bunch of them right there that interferes with the production of the main one, delaying it or movng it. There are always trends of the day and generally wings move over time to be more functional, lots of ideas get taken too far or better ones are found. At the end of the day its going to boil down to getting that right combination of it all. If you wanna win its not going to be how it looks that you worry about.

Everything we do in aerodynamics is the same thing, manipulating the way the air tries to reach equilibrium to create low and high pressures on our working surfaces. If you don't control it, it will make them where you least want it to and hurt the wing performance. Sometimes you have to put designs you dont like on the car too, just because you ran out of time/money or somebody with authority says it looks nice. Hell for all I know those end plates could be just as much or more about the diffuser than the wing. Sometimes I'll put something really eye catching and bazar that has no effect on performance just so everyone tries to photograph and copy it, instead of some other part of the car that really does work.

What I like about these wings is that this style of wing is somewhat unique to F1 and I think that the rules make them interesting. They trim their downforce at the front, that lets the rear wing be fixed which plays huge with the diffuser. if you had to adjust the rear wing you could not have those louvers. You would need a bunch of different end plates for every time you made a minor trim change.
Last edited by richard_leeds on Fri May 11, 2012 4:39 pm, edited 1 time in total.
Reason: Removed image quoted from post above
gixxer_drew
 
Joined: 31 Jul 2010
Location: Yokohama, Japan

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