Wing aero

[shelly]

@variante: as Pierce said, there is no higher pressure outside the vortex - pressure is at its lowest on the inside and then goes up to a value close to ambient. In most cases the lower pressure is felt against the airplane /car surface, and that's what generates vortex lift /downforce.
In the picture you posted there are 2 colorscales (pressure and total pressure): which one refers to the plane surface and which one to the plane cuts in X=constant planes?

[aussiegman]

Another good example of how long these vorticies can persist

[Kiril Varbanov]

These wingtip vortices, on the other hand, create lift-induced drag

Sounds like you are saying that the source of drag is the vortex itself, when i think it is just the symptom of something else creating drag (the wing).

Indeed, the language wasn't correct. Lift-induced drag is caused by the wing.

I've underlined the part I mean to challenge. Is this true? Is there high pressure in the edge of a vortex?

Yes, it is. That's a general theory, more on that later, as I will have to re-read the entire thread again - I think I've missed the original idea or lost it while driving.

[variante]

as Pierce said, there is no higher pressure outside the vortex - pressure is at its lowest on the inside and then goes up to a value close to ambient. In most cases the lower pressure is felt against the airplane /car surface, and that's what generates vortex lift /downforce.

First, thanks for the answers.
I've understood that the outer pressure is not superior to ambient pressure, but still it is at high(er) pressure compared to the core. Since we need to have low pressure in "contact" with the surface of the wing, how can this happen, how can a core get rid of its high(er) pressure layers and "communicate" with a solid surface?
(if someone has good articles that don't go too deep into the mathematical aspects, please...)

[shelly]

Try this:
http://www.acsol.net/~nmasters/vortex-lift/delta.html

and its parent directory, with bibliography:

http://www.acsol.net/~nmasters/vortex-lift/

[shelly]

Some pictures from this forum:
posted by marekk, aug 11, 2011

posted by Crucial Xtreme, mar 5, 2012

[shelly]

and finally this very interesting from spa 2010, showing the y250 vortex (maybe..), posted by whiteblue on sep1, 2010 and highlighted by mep

Have you guys noticed this:



Uploaded with ImageShack.us

Brilliant shot.

with his subsequent comment:

I think this is the vortex sealing the floor.
You can see it passes trough the sloped side pot and the vane.
I don't think this happens by accident. Its designed like that.
The edge of the splitter/floor seems to guide the vortex to exactly that direction.
Possible it depends on car speed to hit exactly trough the vane and side pot.

I think those free edged of the front wing produce the vortex.
Normally you don’t want a wing tip like this because it creates a big vortex.
On airplanes they add winglets to prevent this.
This vortex must be massive to be so easily to spot. Similar size than the ones we see on rear wings.

http://img186.imageshack.us/i/mclarenvo ... rator.jpg/

Anyway I wonder why we don't see it on the other side.

Spa is a clockwise turning circuit. The vortex is different in intensity at different places. I havn't checked where it is most intense but I guess it must be fast, wet and right turning.

The vortex is there all the time we normally just don’t see it. The car running clockwise or counter clockwise has absolutely no effect on the vortex. The rotation direction of the vortex is defined by the wingtips. You have low pressure below the wing and high pressure above it. On the edge of the wing those pressures want to compensate each other causing air flowing from below the wing to the upside and creating a vortex.

So when you look from the front of the car to the left side you will see a vortex rotating counter clockwise. On the right side you will have one rotating clockwise.

Such a vortex is like a mini Tornado. In the centre they have low pressure. This is used to seal the floor. It’s very impressive how they guide it to the floor edge especially without any bargeboards or turning vanes. I guess this is really hard to achieve and demands lots of fine tuning of the front wing edges. I also think the edge of the splitter helps a bit. You notice the little step on it? We must take into account that the actual vortex can be bigger, we see just the centre core. It’s a nice piece of engineering art.

To make the vortex visible it’s not necessary to have a wet track. Hot air with high air humidity can also make vortices visible. Conditions you might have in countries like Malaysia. In the vortex the pressure drops and with the drop in pressure follows a drop in temperature. Air can take up a special amount of water as air humidity. The amount of water depends on the temperature of the air. Hot air can take more. So when the temperature drops the air will release the water what causes some kind of fog. This makes the vortex visible.

Lots of info in the past threads of f1technical!

[Kiril Varbanov]

@Shelly - excellent images (+1 for them), especially the Mclaren one and the so-called Y250 - one of the most important deliberately induced vortices in F1, which we have also discussed in the past, but indeed, not much been said about using them to produce downforce, as you mentioned in previous posts.

On a side note, while looking through some old notes, I found a reference to Helmholtz, who has been very intrigued by vortex formations and has contributed with his three theorems: a fact, which I must admit, I have forgotten.

Anyway, do we want to drive to vortex induced suctions, rollups and types - general theory or just F1 related stuff? Honestly, in the old CFD files I've got there's not much in that regard apart from some common-sense streamlines - teams tend to hide information

[CBeck113]

I like where this thread is going - I would say let's not limit it to theory or F1 usage, but keep connecting the theory to the practical use.
I have been looking for my "old" Aerodynamics books & more importantly notes from school; I studied mechanical engineering with a major in vehicle technology here in Germany, but ended up on the quality side of the fence, so I need to read back up to contribute more here. But, it definitely won't hurt refreshing more of the theory I enjoyed - my prof was working for Eurocopter, so we did quite a bit on wing design (but stressing lift). Loved that class...
One of the (few) things I do remember is that it is very easy to generate vortices on a moving vehicle: I believe the angle needed is between 20 and 30° from vertical, but I need to verify this when I have my notes. Getting enough energy in them to seal the floor through the length of the vehicle and getting them to hit the right spot are the keys to taking this negative effect and making it into a performance enhancing tool.

Thanks guys, keep it up!

[Tommy Cookers]

pressure difference away from vortices gives efficient lift - ie flow 'attached' to the wing, not persisting after the wing has passed
vortices are unavoidable, but should be minimised, because they can only corelate to inefficient lift
because vortices are flow detachment from the wing, in large part persisting and dumping energy not used for lift

98% of the time aviation does not want inefficient lift, but for the other 2% it's desperate for the highest possible lift coefficient
in the 98% the lift coefficient is relatively low (small AoA) because the plane is flying fast, and vortices are small
race cars are aways in the desperate zone, due to the rules limiting wingspan etc
so there's a lot of waste energy that can give benefit downstream of the wing

nature uses some of this downstream waste energy, that's why geese, swans etc fly in V formation
there is now some interest in flying combat aircraft like this when cruising
because they have a low aspect ratio (like a racecar wing), so waste much energy in vortices

[shelly]

I would like to focus on downforce generated through the use of vortices on f1 cars, using as little theory as possible, but also discussing some theory.
Gordon McCabe, with his blog mccabism, is very good at mixing f1 and theory in my opinion. I have found recently an old post of his about longitudinal vortices and downforce:

http://mccabism.blogspot.it/2010/12/vor ... icity.html

Maybe this article is a bit too much on the theory side, but it explains well a basic concept, that I have tries to stress (maybe too many times) on this forum also:

"It is a theorem of inviscid fluid mechanics that the helicity of a vortex tube is preserved over time. However, if a vortex tube is stretched, (as I presume it must be when it is sucked underneath the floor of a racing car), then its cross-sectional area decreases, and the magnitude of the vorticity ω increases, lowering the pressure at the centre of the vortex"

this theorem is one of the three Helmoltz theorems about vortices that Kiril recalled, and it tells us something very significant about vortices in f1 cars. Not only they produce downforce, but if they are accelerated they get stretched and produce more downforce.
On a f1 car, the flow gets accelerated in several places: basically on all the rounded leading edges (wings, sidepods, floor), on the kink line of the diffuser, and (in my opinion) at the diffuser lateral edges, where the acceleration is given by the exhausts.

[Tommy Cookers]

I would like to focus on downforce generated through the use of vortices on f1 cars
...... very significant about vortices in f1 cars. Not only they produce downforce ........

please feel free to focus as you wish, sincerely
I do expect to continue in my view that vortices are (broadly speaking) at best an unavoidable side effect (symptomatic) of lift

[flyboy2160]

An aerodyamicist at one of my former employers once quipped : "Stop whining about vortices! Vortices can be your friends!"

[Tommy Cookers]

presumably he was not speaking (in aviation) of tip vortices ?

[abw]

Just wanted to chime in to say that this thread is excellent, and that I look forward to more, more, more. The type of aero that is relevant to my day-to-day (steam turbines) is nothing like F1 aero. But everyone faces the same challenge at airfoil tips. We can mostly beat the problem with careful control of tip clearances, labyrinth seals, etc. But things expand, wear, rub, etc.

Anyway. Thanks to all who are contributing to this discussion and teaching me. Carry on!