Wingtip Vortices

[trinidefender]

...... commercial aircraft companies have committed substantial amounts of money and effort over the past few years to address the similar issue of wing tip vortices ....
The current generation of wing tip designs used on commercial aircraft like the 787, A350, A320 NEO, or 737 MAX reduce cruise fuel consumption by 2-3%. .....

2-3% is for the first generation of wingtip fences and the like similar to what is seen on Airbuses (except the A350). The latest generation such as the extended and raked wingtips as seen on the new Boeing 777, and winglets seen on the 787 and a350 are worked out to be up to 5%.

2-3% compared to what ? (I wonder on these occasions)
and 2-3% in cruise is useful, but maybe 1-2% of overall fuel use

younger readers might not know that all this stuff was explained by Lanchester in about 1895
so designers have been deciding wrt extent and rake or taper of wings more-or-less since then
(eg the new aircraft in flight rather resemble the DC-3 (or DC-2 really), of 85 years ago)
the dominant factor in these decisions is often evolution (or lack of it) in various airfield space factors
extended tips have been made to do no lifting in cruise (handy if you're extending an existing wing)


tip vortices are an inevitable symptom of lift or DF and a measure of its inefficiency
2d flow producing pressure differences that we call lift or DF
these pressure differences cause 3d components of flow (ie spanwise) - the tip vortex, a waste of energy

though not inevitable if the lifting surface is of skirted DF venturi tunnel type
this will develop inherently less 3d flow
with a decent aspect ratio and maybe extra internal 'lane divider' skirts this will give a better ratio of DF to wake size/energy
handy for car racing
the cars would need to be of TARF, Nardi, (or Yunick ?) 'catamaran' layout (to accomodate the venturi tunnel centrally)
yes, I have seen the pictures in bh's posts

2 to 3% fuel burn reduction on a typical airline flight. An example can be the 737-800 series. They don't come from the factory with the vertical winglets. Those are made by a separate company and is considered an STC (supplemental type certificate). There was shown to be about a 3% decrease in fuel consumption over the average trip by the addition of those winglets.

Note however they are not an easy retrofit. The outboard portion of the wing has to disassembled and then extra structural work has to be done on the wing to support the extra available lift that can be produced near to the wingtip. It is only then that the tip, extra lights and the rest of the panels can be added back on.

[trinidefender]

Separate post for different topic.

If more flow around the outside endplate and under the footplate of the front wing, I.e. When the RedBull wing isn't touching the ground, creates more downforce then running the front wing closer to the ground should not increase downforce.

[bhall II]

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.

I'm out.

[livinglikethathuh]

Raked wingtips increase the efficiency of the aircraft through various ways, of which not all are really related to F1.
-increasing area a little bit, reducing Cl
-reducing wingtip vortices by reducing the pressure differential at the tip, reducing induced drag
-reducing transonic drag by (somewhat) increasing sweep.

As you know, there's a neutral section on the front wing and the multi-element winglets rising just after that will bring a huge jump in pressure differential, and vortices developing on the inside of the cascades will both reduce downforce and bring induced drag. The wingtip vortices are also due to the same effect, pressure diff jumps. As this is directly proportional to Cl, we can say that wing vortices form due to jumps in Cl through the wing span.

In airplane wing design, engineers try to get a smooth Cl-span curve over the wing, and they aim for the minimum Cl near the wingtip. Thinner airfoils and wing washout (wing twisted downward from root to tip) are employed to reduce Cl at the tip and thus, induced drag. Aircraft designers are not concerned in cruising Cl, the dynamic pressure and wing area are more than enough at cruising conditions, and they can always use movable devices (flaps&slats) when more Cl is needed and efficiency is not a big problem. However in F1, we can't afford to lose Cl anywhere as we have downforce targets and are limited in wing area, so we cannot employ this. We currently don't have active aero either, but that's another point.

Drag has always been a concern in F1, but it is sacrificed for extra downforce which almost always pays off in today's F1 circuits. But with the extra concern of the vortices messing heavily with the following cars' aero, there's an additional reason to reduce these vortices.

You can't erase what engineers have learnt through the years of tightened aero regs, they will always use turbulence sensitive and vortex-making aero devices no matter how lax you make the aero regs. So I believe the solution in reducing vortices, thus enabling cars to follow each other closer, is through the close investigation of the generation of these vortices by the governing body, for (an unrealistic) example, testing every front wing at given flow conditions and measure the vorticity at a given distance(which would be more or less the distance a car follows another) and set a maximum value for this vorticity. They already collect all noses for crash tests, they can also collect front wings.

OTOH, a wing's Cl is directly proportional to the vorticity it creates over the air going over itself, that is, the amount the airflow is rotated downward. This, in itself, does not create a vortex spiraling through the side of the wing, but theory says that vortex filaments (my english is not enough to explain what it is) cannot be open ended and of finite length, they can be either closed (creating zero vorticity in total) or of infinite length. A vortex filament of infinite length along the wingspan is only possible through an infinite wing, or the filament may be turned backward, creating the wingtip vortices. The formation of this wingtip vortex may only be mitigated by something that creates another vortex of opposite direction, which is what airplane winglets do. They are small wings, they create lift directed away from the aircraft, and create a negative vortex (They also create forward thrust in turns, yielding proverse yaw, but not F1's concern). For a given Cl, I can think of nothing other than wingtip devices to reduce the wingtip vortices of a given wing, regardless of what kind of vehicle it's mounted on.

Oh, and then there's ground effect. Bhall et al. have discussed the effects of ground effect on wingtip vortices ad nauseum, and in that case the only thing I can say about GE is, as all other GE-related things, is that it is highly dependent on ride height, which is subject to change by bumps, suspension movement, wing flex and DF itself, which makes it hard to implement and harder to keep under control. Active suspension on the cars can mitigate this, but the tyre is still an uncontrolled suspension element and a thinner tyre sidewall is needed to eliminate the tyre flex variable, which would require entirely new/different suspension, and so on.

Lastly the rear wing, a major contributor in dirty air behind the car, may be assumed out of ground effect and its vortices cannot be mitigated with GE.

[riff_raff]

llth- Thanks for the detailed reply.

In my last post the only point I was trying to make was the similar efforts being made in commercial aircraft and F1 cars to optimise the wing trailing wake vortices. As you point out the operating conditions are very different between the two examples.

If you want to see another recent example of aero design effort applied to tip vortices, take a look at the blade tips being developed for helicopter rotor blades.

http://www.wired.com/wp-content/uploads ... 2/main.jpg

[livinglikethathuh]

What I'm trying to say is that F1 designers have their hands tied much tighter than aircraft designers. Moreover, even if you set them free, F1 designers will look for more downforce rather than considering the dirty air the following car encounters.

On a tangent; by any chance can the Toro Rosso cars be designed to lose less downforce in dirty air, for better overtaking?

[Tommy Cookers]

if (as we seem to be told) all DF devices have for equal DF an equal vortex product
and given that DF vortices develop an upwards velocity component (opposite of lift vortices) ....
one might conclude that nothing was wrong with the fundamentals of F1 car aero in 1967-8 (ie before the panic banning after Spain)

high mounted, high aspect ratio, smallish camber and AoA
stated to be high mounted for better effect and eg minimise adversity close in the wake of other car

Paul Frere wrote that if engine power was limited eg to 200 hp the aero package chosen would be efficient
the practical effect of aero was a cycle of officialdom tightening corners, (further) incentivizing inefficient DF

[trinidefender]

if (as we seem to be told) all DF devices have for equal DF an equal vortex product
and given that DF vortices develop an upwards velocity component (opposite of lift vortices) ....
one might conclude that nothing was wrong with the fundamentals of F1 car aero in 1967-8 (ie before the panic banning after Spain)

high mounted, high aspect ratio, smallish camber and AoA
stated to be high mounted for better effect and eg minimise adversity close in the wake of other car

Paul Frere wrote that if engine power was limited eg to 200 hp the aero package chosen would be efficient
the practical effect of aero was a cycle of officialdom tightening corners, (further) incentivizing inefficient DF

"all DF devices have for equal DF an equal vortex product"

If I understand what you are trying to say then all downforce devices for an equal downforce DO NOT have an equal vortex product.

[livinglikethathuh]

if (as we seem to be told) all DF devices have for equal Cl an equal vortex product

I think it should be more like this

[riff_raff]

What I'm trying to say is that F1 designers have their hands tied much tighter than aircraft designers. Moreover, even if you set them free, F1 designers will look for more downforce rather than considering the dirty air the following car encounters.

I don't think that is entirely true. While the F1 aero regs are restrictive in regards to size and location, commercial aircraft aero devices must operate over a far greater range of conditions with much better efficiency.