W06 Influenced CFD Study

[PlatinumZealot]

Chuck that is ANSYS you are using for the CFD?

Ansys is probably better than Solidworks for fluids, but I haven't come across a reason to learn Ansys yet since most the simulations I have done were not used for making mathematical models or anything like that. The ease of Solidworks is very handy.

@ Bhall, I have had good success using CFD for projects on this forum before. Renault's front exiting exhaust, Mclaren's F-duct, Mclaren's coanda exhaust, the blown diffuser were all analysed before by either me or Ringo... CFD is a tool and the big organizations tend to customize it for their needs, but you don't need a engineering team or a huge server room to get good accurate results for simple models.

Other than doing a few CFD sims for this forum in the past, I have used Solidworks to good effect at work. Mind you, CFD is not really part of my job, but I try to have fun with it now and then. I have used solidworks for transient heat transfer combined with viscous fluid dynaics and the results were very close once I tuned my fluid model. Solidworks has a section where you can set your power law equation coefficients which is neat. I got all the coefficients from sending out the fluid to a lab for viscous testing then I put this into my model.

And these were the results.... this is transient study of ketchup being cooled. This is just for one point in the body of the fluid. I was only interested it he core temperature....



Basically saying, Chuckdanny can get realistic results if his model is good enough. Even to just see a few trends, it's not like scientific reasearch or rocket design so accuracy is not critical for his demonstration.

[PlatinumZealot]

@Chuck, Bhall is right in that the model is missing some things. I would probably draw in the front half of the car at least. Put in the tyres, the brake duct, the nose, front slitter and barge boards.. just basic shapes should be enough to get a trend from.

Make the wheels spin. Make the road move. Add surface roughness.. etc..

[lkocev]

I think chuckdanny's efforts are quite commendable and irrespective of model inaccuracies, has still drawn quite an elaborate and complex wing. This wing may have been drawn to the best of his abilities, it may have been somewhat rushed, but the point is, he made an attempt, and quite an impressive one at that. Frankly bhall, I don't see you doing any CAD drawings, or putting aside your computing power in order to evaluate them. I agree with you that the model is not quite complete, or even accurate, and accordingly we can't draw conclusiveness with regards to the W06 wing. But guess what; not chuckdanny or any of us for that matter, have an accurate CAD file of the W06 front wing.

This is supposed to be a discussion, that one's impressive efforts are met with such negative criticism is quite disheartening. I think chuckdanny you should continue working on your model, and continue evaluating it. Each time you do, you will develop your skills with drawing and exploiting modeling functions of your chosen CAD software. You will develop your perceptive ability of observing images, and ability to approximate those as dimensioned sketches through space in your own mind. You will essentially become a better, more skilled operator of CAD and CFD software, whilst bhall will continue to negatively criticize from the comfort of his armchair, in the knowledge that he will never develop the courage, skill or discipline to commence doing, what you have.

You have made a nice start, I encourage you to keep the effort going and continue to improve your skills. Props to ya brother.

[chuckdanny]

You are misquoting me i said:

The arches are the solution to the problem of the non extension of the endplate to the low pressure area (lower than the wing tip i mean), instead they've upped the low pressure area near an even higher pressure area this time inside the endplate. Instead of an hanging endplate we have a protuding lower wing toward the endplate (up)
But doing so it is located even closer to the front wheel (they may have found it usefull or better solution nonetheless despite adverse pressure gradient, maybe because feed differently it is still stronger than the old one), so they bend it outside which could be the major wheel wing interaction with wheel trailing vortices

Because you have 2 choices here, either you put the wing tip higher like we have seen in previous year

http://upload.wikimedia.org/wikipedia/c ... 06_EMS.jpg

which allow a bit of an hanging endplate for flow segregation and endplate vortex formation or you put the wing lower for a bigger ground effect, closer to the ground and create this "Russian nesting doll" (because they are very good at aerodynamics) which is feed (my guess) by the outside gutter vortex plus the endplate slots but still is (my opinion) located into the arches.

I'm not drawing conclusions, i hazard my guess with cfd while you hazard yours with pictures, i'm not even pretending that i should be right and you wrong because of that, this is just my way of gaining better understanding but still of course i may be wrong who cares? Are you always right so that it allows you to insult others who are expressing different views ?

[turbof1]

After consulting with Steven, we decided to split the discussion off into the engineering projects subforum.

The reason so is that we indeed will not be able to simulate the wing's real life counterpart to its exact flow details. However, we might learn a few patterns and a few of the solution the wing applies.

Furthermore, splitting the topic and giving the topic title a subtle different name, will protect it from ranting that "it isn't worthwhile since you can't ever simulate the real deal". The previous topic descended into bickering due insistance of how "wrong" the project was. It is not wrong, and honestly I really don't appreciate the smear campaign against it.

This means all together:
-Chuckdanny will continue on his fine work here, in all earnest.
-Criticism is allowed, but it has to help the project, not work against him.
-Effectively, any ranting that hurts the project will be removed!

[chuckdanny]

That's what i was trying to explain and in this regard i could have only used a crayon
Can you see the trend? of course when you put a wing in front it takes the punch so that the adverse pressure gradient (red) migrate downward, more so with a vortex which somehow convert streamwise velocity hence dynamic pressure into spanwise with helicity



Its just that i have a great colorful crayon !

(thanks turbof1!)

Edit
@Platinumzealot
I use star+. I believe ansys fluent has a cuda support, could be a better solution because a graphic card processor architecture is better adapted to cfd computing from what i remember. But i don't think that it can benefit from the combine ram ?

[Just_a_fan]

This is how to start the process. Excellent indication of how quite simple flow behind the wheel becomes much more involved once there is interaction between structures.

In order to develop an understanding it would be nice to start with a simple wing in front of the wheel then add an end plate, then make the endplate an out wash design. Work through several small changes to develop a more complex wing. That way the effect that changes in the wing have on the flows can be identified. It's a more time consuming process, sadly, but I think it will bring much more understanding of the system. =D>

[PlatinumZealot]

The bit by bit thing should be done only in certain circumstances.That way is too inefficient for this study of how the front wing works, and you won't learn much because in isolation on their own, the parts will affect the fluid in a totally different way than when they are put together in a system. Too much time wasted.

It is best to draw the parts that you think are relevant to the study as accurately as you can. Then you carefully create the relevant global conditions, fluid settings and boundary conditions that you think are relevant, as accurately as you can, then run the simulation coarsely. If things pass your scrutiny then you go over and refine and run again.

[turbof1]

The bit by bit thing should be done only in certain circumstances.That way is too inefficient for this study of how the front wing works, and you won't learn much because in isolation on their own, the parts will affect the fluid in a totally different way than when they are put together in a system. Too much time wasted.

It is best to draw the parts that you think are relevant to the study as accurately as you can. Then you carefully create the relevant global conditions, fluid settings and boundary conditions that you think are relevant, as accurately as you can, then run the simulation coarsely. If things pass your scrutiny then you go over and refine and run again.

I was thinking this too, although for the more complex aspects it would be best to create something simplified, next to the wing model, in order to have some sort of idea what it's doing, like the wheel/wing interaction.

Chuck is working increasing the accuracy of the model; for the moment one crucial component has not been shown yet, which are the underbody strakes. Let's hope the dices fall right in Monaco [-o< .

[chuckdanny]

I had the 3rd element, let's call it a wing (although it is angled, inclined more like a flap) very wrong for this 1st test which should change the picture by much because the flow was separated there (i even thought for a moment that it could be a feature like a newbie bzz bzz) So i will also be able to push residuals down. I have no profile view of it but i can figure how it works that is with coanda effect, the back face is pretty far from the front face, the second element doesn't seems to help in bending upward at the trailing edge, the 1st and 2nd wing are angled in the opposite direction to create a venturi effect with the ground.
What must be one key also to this wing is that the 2nd element is shadowed by the 1st and must be triggered when the car brakes, subtleties... Well i'm not sure on this point.
I had the leading edge of 1st and 2nd more rounded more like an air lifter but i change for more efficient naca which is relevant for the flaps only.
The y250 vortex must be the classical wing tip vortex arising from the merge of the 2 flaps tips then.

The strakes must segregate the vortices coming from the teeth no ?

Adverse pressure gradient doesn't seem to trigger flow separation


That's what i'm talking about, yes yes yes !!

[chuckdanny]

These little experiments have there limitations, turbulence is a physical problem yet to be solve, is there a unique solution to the navier stokes equation?

I found out how the merc undernose devices works though (highly presumptuous )
This nose in ground effect create vortices under the little arches, merge of high pressure in low pressure area(relative).
The 4 elements device create vortices, on the relative low pressure side under the footplate. This footplate has a leading edge that bends up (vortex stretching and strengthening).
The bird behind create vortices at the batwing tip on the extrados (low pressure side) but because it has no endplate this vortex maybe influence by the preceding can shift to the side instead of being shadowed by the wing of the bird.

So these three devices are creating a vortices connection in serial(it's false) that lower the undernose static pressure hence produce downforce. The y250 is rotating in the opposite sens so repulse and bend outward behind the front wheel.

Guess this without my cfd crayon? I can't, i'm disabled in this regard.

[chuckdanny]

Sorry i was in a rush effectively i didn't even thanks kyocev for his encouragement.
It's the first front wing i ever tested in cfd so i have many things to learn. My model is indeed not close to the real thing but that's because i need analysis to better model some shadowy area like the y250 area. I've been looking at different iterations across the years of front wings and tried to figure out what this wing try to achieve.

That's my understanding of it as of yet (y250 area and a bit overall) :
To generate strong vortex you need two areas of big pressure difference or many distributed all along the vortex path.
The overall working principle of the wing is a venturi, that is a convergent and a divergent.
The neutral central part would be flat or just a convergent if angle of attack was leading edge up that's basic but lets begin with a know fact so to generate downforce the angle is leading edge down. In doing so we have a very short convergent and very long divergent.
Close to it there is the "liberal" part. It is shaped also like a venturi but with the smallest section further back plus the leading edge closer to the ground and openings whose purpose are not cristal clear. The biggest section at the end of divergent plus openings make this venturi far stronger which create the pressure differential needed right at the trailing edge of the neutral part. We have 2 venturis close to each other with different ratio.
To enhance this pressure difference they extend the neutral lower part like an hanging endplate plus an extension spanwise which enhance the crossflow caracteristic. The same design is used with the endplate slot toward the arched area.
This arched area is also designed like a venturi the 1st and 2nd arches being the convergent part.
That's when looking at the first arche that it appears to me and on my own cfd that maybe this 1st arche like the 2nd and 3rd element could stall when the wing is horizontal triggering a stall of everything behind but it seems hard to control and a stall create a big mess so i don't think it's realistic and nevertheless i won't be able to reproduce that. Maybe the strakes are there also to separate a stalled part of the wing from an nonstalled iwon't get into that. Strakes generally extend low pressure area at the throat.
So the general idea is a venturi with openings that prevent separation with high pressure blo-wing.
Maybe you've discussed that already.
So 1st element : convergent all other divergent with high pressure blowing to help take the curve especially the extrados of 3rd element which uses coanda effect also to stay attach, the one i got wrong which created the mess.
This wing gave me the confidence that this was why the y250 was so strong :

(i didn't make the arrow)
It's in fact an endplate, more specifically an endneutralplane plate, that's how y250 enhance downforce like a real endplate vortex. It is not the product of just 2 flaps, its the product of this mechanism that i tried to explain.
But since you've talk about all this things since mathusalem you must already know.

[bhall II]

You can actually see the effects of the Venturi "tunnel" under the nose.

Note how the Y250 vortex is pulled up by the low-pressure zone before it's pulled down by the turning vane downstream.



Ferrari enhanced this effect on the F138, or at least tried to do so, with tapered wing pylons and a judicious placement of the camera pods.



Bonus factoid: one of the primary reasons to implement a short nose is the ability to place the wing pylons, the dimensions of which are limited by the regulations, as far aft as possible for the sake of this very effect.

That's when looking at the first arche that it appears to me and on my own cfd that maybe this 1st arche like the 2nd and 3rd element could stall when the wing is horizontal triggering a stall of everything behind but it seems hard to control and a stall create a big mess so i don't think it's realistic...

No, you got it right.

The prevailing wisdom that Red Bull's infamous bendy-wings flexed in order to increase downforce is incorrect. Frankly, it doesn't even make sense, because such a system would constitute a design that deliberately goes out of its way to create peak downforce, and thus peak drag, at speeds found only along straights where downforce is unnecessary and drag is a hindrance.

It's an idea as sensible as a football bat. (Then again, that does sorta make it perfect fodder for the Gary Andersons of the world.)



In reality, the ride height of a wing in ground effect can only be lowered so much before the narrow gap causes the end plate vortices to burst. When that happens, both downforce and drag are reduced.

If you can (predictably) bend the wings under load to harness that characteristic, the result is the capability to run very aggressive wing settings without the usual prohibitive drag penalty. It's almost like Monaco downforce meets Monza drag.

The principal point is that front-wing ground-effect depends upon two mechanisms: firstly, as the wing gets closer to the ground, a type of venturi effect occurs, accelerating the air between the ground and the wing to generate greater downforce. But in addition, a vortex forms underneath the end of the wing, close to the junction between the wing and the endplate, and this both produces downforce and keeps the boundary layer of the wing attached at a higher angle-of-attack.

The diagrams above show how this underwing vortex intensifies as the wing gets closer to the ground. In this regime, the downforce increases exponentially as the height of the wing is reduced. Beneath a certain critical height, however, the strength of the vortex reduces. Beneath this height, the downforce will continue to increase due to the venturi effect, but the rate of increase will be more linear. Eventually, at a very low height above the ground, the vortex bursts, the boundary layer separates from the suction surface, and the downforce actually reduces.

So, yeah. Stalling the wing is definitely doable.

Incidentally, I really wish I had read that article more closely the first time I stumbled upon it. The last two paragraphs would have saved us all a metric ----tonne of trouble.

So, for a wing in isolation, the ground effect is fairly well understood. One imagines, however, that the presence of a rotating wheel immediately behind the wing makes things a little more difficult!

The diagram here, from the seminal work in the 1970s by Fackrell and Harvey, demonstrates that the rotating wheel creates a high pressure region in front of it, (zero degrees is the horizontal forward-pointing direction, and 90 degrees corresponds to the contact patch beneath the tyre). Placing a high-pressure area immediately behind a wing will presumably steepen the adverse pressure gradient on the suction surface of the wing, causing premature detachment of the boundary layer. Hence, when the wings were widened in the new regulations, most designers immediately directed the endplates of the wings outwards, seeking to direct the flow away from those high-pressure areas.

Maybe the strakes are there also to separate a stalled part of the wing from an nonstalled iwon't get into that. Strakes generally extend low pressure area at the throat.

You might already have the answer.

If the dynamic pressure of the air flow on the high-pressure side remains more or less undisturbed, what will happen to the end plate vortex if you reduce the dynamic pressure of the flow that feeds it from the low-pressure side?

To generate strong vortex you need two areas of big pressure difference or many distributed all along the vortex path.

Bonus: what happens directly under the chassis if the same principle is applied?

[hollus]

That batwing would produce vortexes co-rotating with the Y250 ones, so that they would attract (edit: or do they repel?) each other (for aiming accuracy?) and potentially fuse into stronger vacuum cleaners for the floor's edges. Is that what you were after, bhall?
The bat wing would also push the flow somewhat downwards in a region where it was going upwards, possibly making it horizontal and avoiding low pressure above the tea-tray.

But if it is such a powerful weapon, and very tunable too, why haven't the other teams copied it yet? What are the minuses? I can see a bit of drag but that's all.

[chuckdanny]

You can actually see the effects of the Venturi "tunnel" under the nose.

Note how the Y250 vortex is pulled up by the low-pressure zone before it's pulled down by the turning vane downstream.

I think it pulls up because it is the upwash of the wing, it follows the general trend here. I don't understand how a low pressure under the nose would pull the y250 up. I'm not saying it's not happening, i don't understand.
The upward bent should reinforce it either.
The turning vane bends it outward and doing so stretch and reinforce like on this toro rosso cfd :

http://oi57.tinypic.com/241m2pd.jpg

While this ferrari nose is short (i don't see it though) it is not low. Mercedes pylons don't bend inward instead it uses the upper lip of nose intake to accelerate plus a lotus like pelican throat. It's what i call a real nose in ground effect, it creates a high pressure over the neutral part of the wing and low pressure under the wing and the nose. Pressure differential between outside and inside flow of the pylon plus the arche entry and a peculiar ramp before it should trigger 2 vortices that are connected in serie with footplate of the turning vane/venturi vane behind. Enhancing the low pressure under the nose plus helping the flow to go around the nose more than above reducing the lift over it. That's my view on it, i'm not saying it is the absolute truth.

So, yeah. Stalling the wing is definitely doable.

Ok so you think that's what they do. That's amazing, how this thing reattach almost instantly at corner entry is quit an achievement. I can see how all the mess is diverted outside following the extrados of wing and flap but whoa. Maybe that's why they lift and coast, pure hard braking wouldn't allow this thing to work
W've seen lewis being caught quit a few times in qualifying last year (austria for example).

For the turning/venturi vane - bird interaction i'm convinced that an inner vortex exist like on a rear wing(turning vane not bird) but i cheated to make it happend (diane krueger effect ) with a gurney on the last element.
THis one triggers at the meating of high pressure to low pressure where the last element (elephant ears) meats the undernose. Maybe the interaction with the peculiar mercedes wishbone play its part here. That puts me into some hard guess about vortex formation that is it often developp (it's of course a dynamic unsteady process) downstream to upstream, the favorable flow condition(pressure difference) takes times so space to developp hence it triggers downstream and then propagate upstream. That's why the bird trigger also the inner vortex. Well as always that's my take on it...

@hollus: it works in conjunction with a "short nose in ground effect" and lotus didn't focuse or have the time/finance to look at it ?