Active aero

[bhall II]

Ehm, Bhall: the indy car you showed actually had an endplate at the beginning of the season. It was actually forbidden when too many endplates with cascades broke off. I would not inmediately call it unnecessary.

Unnecessary ≠ unhelpful

Without an end plate, you don't get the force enhancement from cascades (blue). But, you still get it from the wing tip geometry (yellow), which is outrageous on the IndyCar.


(Click to enlarge, but don't make fun of my drawing skillz)

[Just_a_fan]

That Indycar does have an endplate. It's parallel to the road surface. Look at the curve of the wing and then straighten it out. There's the endplate. Just because it's not a big fence sticking upwards doesn't stop it performing the same function of pressure separation.

The endplates on F1 cars aren't really endplates in the way they used to be and still are on aircraft (in the form of tip plates etc.) Back when we had basic straight wings, the endplate was the big thing at the end of the wing and was there to keep the pressure separate. The big thing we call an endplate now is being used to direct air around the front tyre. The job that used to be done by the endplate is now done by plate that is parallel to the road surface thanks to the curved section wing that is being used to create a vortex entrainment tunnel.

[turbof1]

Ehm, Bhall: the indy car you showed actually had an endplate at the beginning of the season. It was actually forbidden when too many endplates with cascades broke off. I would not inmediately call it unnecessary.

Unnecessary ≠ unhelpful

Without an end plate, you don't get the force enhancement from cascades (blue). But, you still get it from the wing tip geometry (yellow), which is outrageous on the IndyCar.

http://i.imgur.com/hdcI6ER.jpg
(Click to enlarge, but don't make fun of my drawing skillz)

Well, going from that standpoint wings aren't necessary at all to create grip, just extremely helpful .

[bhall II]

That's not wrong.

The only element of a current front wing that behaves like a proper end plate is this...



Everything else is something else, and teams have previously used "end plates" that don't even try to prevent the high- and low-pressure streams from merging.







I think they'd probably still look something like that if the regulations didn't more or less require the "end plates" we see today.

(And if we're saying that foot plates function as de facto end plates, I dunno about that one.)

[trinidefender]

Bhall I think you are confusing a vortex rolling around the whole outside of the wing shown in one of the graphics with airflow lines (I'm going to assume some sort of CFD image) and what is demonstrated in the study you linked to. For one there is a major difference in the wings used. The wing in the study is a straight wing. It also shows a vortex beneath the wing which is fed by airflow coming from outside the endplate. In a previous post I mentioned that yes there would be a vortex beneath the wing.

In the graphic you posted there shows a large vortex rolling around all the way from the top of the wing to the outside and then underneath the wing. It is this vortex which reduces the wings effective span, not the small vortex shown on the bottom of the wing just inside the endplate. Yes there is a difference between them.

3rd you didn't account for the vortex tunnel. Even if the outside of the footplate bends down as far as touching the road surface the vortex tunnel underneath the wing will ensure that it isn't to low to the ground to kill that vortex below the wing and neutralise its benefits.

4th that RedBull car was actually known for having having slower top speeds if my memory serves me correctly and at the same time looking like it was on rails in high speed corners. So yes the downforce gained by having the flexible front wing provides a larger benefit in the corners, braking and accelerating than the loss due to the increase of drag that was present on the straights.

If what you say is true then running that RedBull wing to close to the ground, I.e. Touching the ground in many scenarios, killed the vortex (even in the modern generation of wings with vortex tunnels) then we will have an effect where you will see the wing bouncing up and down constantly. as it gains downforce. Allow me to explain. As the car accelerates the downforce will increase. As the load on the wing increases the outside will bend down toward the ground. At some point this will kill the vortex. According to your research (which again I say is using a wing differently shaped than what we have), this should stop a lot of the downforce and then further stall the wing as the vortex BENEATH the wing isn't there anymore the help keep the flow attached at such high alpha angles (such high angle of attack). This reduces downforce even more. Through this reduction in downforce the load on the wing will decrease, meaning that the flex downward would disappear and the wing would straighten out. The vortex would form again, downforce will increase then it will move back toward the ground and the cycle will repeat. I've never seen that happen.

This reply took more time than I had to spare

[bhall II]

This reply took more time than I had to spare

Well, don't feel obligated to respond. But, I do appreciate the consideration.

The answer to your Red Bull conundrum: anisotropic carbon fiber layups that flexed as a result of both the vertical and horizontal loads placed upon them. Regardless of what either one of us thinks was the purpose behind the wings' flexibility, that's the only way they could have passed the relevant tests.


2010 test


2010 flexibility


Revised 2011 test

"Revised" 2011 flexibility

I'll never understand why Charlie Whiting didn't implement a rule like 3.17.3 for the front wings, too. It would have ended the issue instantly.

Anyway, here's a more in-depth write-up.

As to the aerodynamics, you have to rewire your thinking here. The objectives behind, and the conditions relevant to, an inverted wing in ground effect aren't the same as that of an ordinary airfoil in freestream conditions.

Check out the study by Zhang and the summary by Zhang, Toet (former head of aero at Sauber), and Zerihan (former aero team leader at Mercedes). I promise I'm not making this stuff up.

The rest requires a bit of lateral thinking on our parts, because no one in a position of authority will ever spell it out for us.

[trinidefender]

I also believe you need to alter your thinking. You are applying logic from research that is applicable to a straight wing then trying to apply it to a wing that has a large vortex tunnel to stop the vortex underneath the wing from breaking down. In your research it clearly states that if you move their wing to close to the ground that the vortex underneath breaks down, that i will agree with for that scenario for the simple reason that in their case it is the endplate itself that hangs below the wing allows the vortex to form in the way it does and once the endplate gets to low airflow is blocked from rotating around the endplate. i agree with that as i just said.

Where the new wings differ is that they have the best of both worlds, they have the vortex tunnel to form the vortex which allows the airflow to stay attached at very high alpha even at very low wing heights yet at the same time the bending and lowering of the outer portion allows the stoppage of much of the airflow coming in from the top and side of the wing and helps to keep the pressure differential at its highest.

I never said your research was wrong. Your research just says that with its wing once the front ride height gets to low the downforce decreases rapidly as a result of vortex breakdown. I am saying that the vortex tunnel allows lower front wing heights without a breakdown of the vortex below the front wing.

[bhall II]

Those aren't "vortex tunnels;" they are the effective end plates.

A vortex forms when a high-pressure stream merges with a low-pressure stream. High pressure comes from over the wing; low pressure comes from under the wing.

When the wingtips hit the track, it cut off the high-pressure stream by directing it straight into the asphalt. Thus, vortex breakdown and downforce/drag reduction.



The wing didn't completely stall, because it was still in ground effect with low-pressure forces acting upon the suction surface underneath. The vortical breakdown cased by reduced ride height just meant the wing was in the force reduction region.

[Nickel]

If what you say is true then running that RedBull wing to close to the ground, I.e. Touching the ground in many scenarios, killed the vortex (even in the modern generation of wings with vortex tunnels) then we will have an effect where you will see the wing bouncing up and down constantly. as it gains downforce. Allow me to explain. As the car accelerates the downforce will increase. As the load on the wing increases the outside will bend down toward the ground. At some point this will kill the vortex. According to your research (which again I say is using a wing differently shaped than what we have), this should stop a lot of the downforce and then further stall the wing as the vortex BENEATH the wing isn't there anymore the help keep the flow attached at such high alpha angles (such high angle of attack). This reduces downforce even more. Through this reduction in downforce the load on the wing will decrease, meaning that the flex downward would disappear and the wing would straighten out. The vortex would form again, downforce will increase then it will move back toward the ground and the cycle will repeat. I've never seen that happen.

https://youtu.be/Ql0n1DsIGsE

This came to mind.

[bhall II]

Yeah, Ferrari never quite got it to work. Then again, I guess neither did anyone else.

McLaren came closest. But, their solution was very different.

[turbof1]

Bhall and trinidefender in a debate about aerodynamics

[turbof1]

Those aren't "vortex tunnels;" they are the effective end plates.

A vortex forms when a high-pressure stream merges with a low-pressure stream. High pressure comes from over the wing; low pressure comes from under the wing.

When the wingtips hit the track, it cut off the high-pressure stream by directing it straight into the asphalt. Thus, vortex breakdown and downforce/drag reduction.

http://i.imgur.com/hjKBg01.png

The wing didn't completely stall, because it was still in ground effect with low-pressure forces acting upon the suction surface underneath. The vortical breakdown cased by reduced ride height just meant the wing was in the force reduction region.

Yes, but doesn't the vortex actually enhances the suction? So when that vortex breaks down you loose a good bit of that.

Of course it's plausible the wing inmediately moves into the optimal zone where it sheds just enough load to keep the wing downwards flexed but not enough to loose it and to start oscilating. Since Red Bull were/are masters at carbon layer manipulation, I wouldn't be surprised. I think Ferrari failed because the wing bended too much. Also I believe the flat footplate section keeps the vortex at sufficient ride height to not fully breakdown.

The biggest issue is to keep your aero predictable. mcCabism had a good article on that:
http://mccabism.blogspot.be/2013/07/fro ... kdown.html

Q-criterion isosurfaces of the vortex breakdown phenomenon, taken from the instantaneous DES flowfield, are depicted here. Bruckner points out that “the vortex breakdown moves forward as the wing is moved closer to the ground…The large vortex expansion…is composed of a recirculation region enclosed by the spiralling tail shed from the vortex breakdown.This causes high pressure fluctuations on the endplate and flap, resulting in a more unstable wing with variations in downforce and drag three times larger than at higher ride-heights.” (p116).

He himself quoted Jacques Heyder-Bruckne's PhD thesis, downloadable from here: http://eprints.soton.ac.uk/207263/

I think the single most important you need to get from that (absolutely awesome) thesis, is the conclusion that lower wing ride heights reduces wheel lift and drag, emphasizing that the flow structures around the rotating tyre shift very suddenly once under a specific ride height, at which point the flow structures will behave more like if the wheel is stationary. Especially important is that both the position of top edge vortex of the wing changes, and that lower edge vortex (the one you 2 are debating, right?) breaks down EARLIER, further away from the wheel.

Do note that in this state drag coming from the front wing is heigher. In an ideal word you'd be looking at flexing the wing flaps downwards too. I think that was mclaren's idea. By pivoting the entire wing, the effective AoA of the wing reduced.

Also important to note is that the numerous vortices around the outboard section of the wing, merge more and quicker with the lower edge vortex at lower ride heights, which as explained above breaks down quicker, reducing drag.

So Bhall might indeed be correct. You are not looking at full vortex breakdown at the peak suction point, but at breakdown behind that before the vortex reaches the wheel shoulder.

[bhall II]

Yes, but doesn't the vortex actually enhances the suction? So when that vortex breaks down you loose a good bit of that.

Think of it in steps.

1. Downforce increases as ride height decreases.
2. Below a certain point, end plate vortices start to grow rapidly as the wing enters the force enhancement region. This increases the rate of downforce production.
3. The vortices burst after they become too large to be sustained by a ride height that continues to drop. While downforce continues to increase, it does so at a slower rate.
4. At peak downforce, separation begins to occur along the suction surface, which sheds downforce and induced drag.

Seeing it all spelled out like that, it looks like there's room for both explanations. The only difference is that one stops after #3 and the other stops after #4.

One thing to keep in mind, though, is that none of the studies cited to this point deal with wings (or wing-wheel interactions) from 2009-2013. They're all based upon pre-2009 inwash designs.

[turbof1]

2009 to 2013 neither would be that specifically relevant since we are dealing with slightly smaller wings again. I think we should appreciate the simplicity of the study I quoted since it starts from a simple fence as endplate with wing elements crudily attached. Perhaps the most important single thing is that our lower vortex gets ejected into the wheel wake when the wheels are straight, both in the study and currently. So it does look that it's very important to make the vortex dissipate before it reaches the wheel wake, where it will create turbulence and drag. I think that's the biggest reason to have the wing run so low: it'll increase front wing drag, but reduces wheel drag by a lot more.

So again, you do want the vortex to be created since it is very important for downforce and hence the loads to keep the wing flexing. The vortex will actually dissipate quicker the stronger it is. That's very important to note.

3. The vortices burst after they become too large to be sustained by a ride height that continues to drop. While downforce continues to increase, it does so at a slower rate.

We probably agree here, but I do feel the need to underline we want the vortex to burst before the tyre shoulder, but not before the peak suction point of the wing. If it burst there, it will remove a very large part of the downforce and hence the loads. And that is where Trinidefender is correct.

[bhall II]

I think you're reaching.

Just to be very clear, the context of my comments should not be considered to include any designs other than Red Bull's bendy wings, and those had a span of 1800mm that encompassed the track width of the entire car. That means they operated under very different conditions to those found in the studies, including the ones I've cited.

Also, remember that F1 designs are inherently compromised by regulations. So, nothing is ever perfect. If adverse interactions are present, then it might be because there's not a whole lot anyone can do about it. (Read: current end plate regulations deliberately reduce performance.)

That said, I can't imagine a wing scraping across the track is going to allow much of anything to reach the wheels, much less fully developed end plate vortices.