(KVRC) Variante

[variante]

If you've got questions or want me to describe a topic depth, just ask

The diffuser..??!!!

What?!? I can't hear you...!!

"...ask me to show everything, but not my diffuser..."

On a serious note, inwash from the rear wheels is one thing I am struggling to contend with - any friendly tips?

Sure. Well...

Inwash is caused by high pressure accumulating on the front of the rear tires, which vents on the low pressure areas about the diffuser.

To decrease the strenght of this phenomenon you can, amongst other options, place the low pressure peak zone of your diffuser right in front of the tire, thus mitigating the high pressure source. Thanks to this configuration, the throath of you diffuser will also be fed with clean air.

You can also study the streamlines of the inwash and design the sides of your diffuser consequently, so that they will use the inwash energy to shed a vortex on each side flowing along diffuser's walls. On turn, the so formed vortices will help you contain further inwash thanks to their low pressure core (sucking and containng transversal flows).

Or...you can place strakes near the tires to “physically” contain the inwash. ...and maybe use those same strakes to shed vortices described in the previous case.

Another way is strategically blowing air (from you bodywork) towards the areas of interest, dampening the negative effects of the tires.

That's all i know about it. As a last note, i've used all of these techniques on my car but the last one.

Although i cannot show my actual KVRC diffuser, i can show you some bits of my F-SAE diffuser (just a concept, for the moment), which is of similar (yet not really identical...) philosophy. Here you can notice how the strong inward flows are transformed into an equally strong vortex.



PS:

How are these flowlines achieved in (I presume) paraview? http://i1372.photobucket.com/albums/ag3 ... du7uuz.jpg

I don't know. You should ask Chris (cdsavage) about them: he created that image.

[chuckdanny]

Very interesting thanks. That's what i saw on my numerical experiment but i wasn't sure. Is is the reason why in f1 the outward strakes are smaller, it allows inflow to developp vortices in the 2 outer vanes instead of completly shielding from this inward flow? Or is it just fia rules ?
In fact inward flow is quit natural with rakes even without tire wake which of course greatly amplify the phenomenon.
Did you figure it out by yourself or is it a known fact that you have read somewhere ? Just to know if this is really what's happening in f1.
You've design a great prototype.

[MadMatt]

For those wondering on the concave convex diffuser there is a thread on this forum about it

[variante]

Is is the reason why in f1 the outward strakes are smaller, it allows inflow to developp vortices in the 2 outer vanes instead of completly shielding from this inward flow? Or is it just fia rules ?

Just FIA rules, unfortunately. Any bodywork more than 250mm away from the simmetry plane of the car must be at least 50mm from the reference plane. The central strakes are at the same height of the reference plane because they are inside the 250mm window.

In fact, if it was allowed, F1 cars would have massive structures to contain the inwash. EBD from few years ago had that function.

The positive effects of the strakes can be clearly observed in this official Toro Rosso image (on its very bottom):

Did you figure it out by yourself or is it a known fact that you have read somewhere ?

...so, yes, official documentation about it does exist. However that is so rare (and with big pieces of information missing) that, if you want to go in depth, you've got to do the job by yourself.

You've design a great prototype.

Thank you!
i also enjoy your "CFD art"

[chuckdanny]

oK! very good. I Found the torro rosso video, great one.
There is another good cfd pic



The color map suggest a streamwise velocity field component (i/Ox) representation and thus that the y250 vortex is faster streamwise than freestream. I never got this but it is squeezed between the nose bargeboard and the wheel.

[variante]

Yes, that video from Toro Rosso and those images from Sauber are the only pieces of actual F1 infomation ever published.

About those Y250 vortices, it's impressive how powerful and stable they are. Their velocity on the longitudinal axis appears to be 4-6m/s faster than freestream (i.e. 7-10%) on most of their lenght. That property, however, is focused on the first part of the vortices lenght (obviously), which confirms the fact that they are created to improve extraction from under the Front Wing. The reason why they are keps stable till the radiator intakes must have something to do with Front Wheels wake management.

However, other collateral effects are still uncertain...pure speculation.

Anyway, still impressive the job of those engineers. I just hope they will publish something about, one day...

[CAEdevice]

Going back to the KVRC: according to my estination, the difference between a "vortex controlled" diffuser and a "standard" one is about 1000N distributed all over the floor... the distance between a placement and a first place

[chuckdanny]

Very true (the vortex makes the wing work harder), i would add that in fact we don't know how much it is quicker, the color coding tells us that the speed is between 5 to 10% up to unknown quicker because all speed above are red.

What we clearly see also is the "dirt remover" function of this vortex, it absorbs all the diffused vorticity created inboard by the wheel, it is a vorticity confinement structure, up to a point.

[variante]

An update after the second KVRC race.



Following balance issues experienced in the first race, the car was modiefied mainly to correct this aspect. Therefore, downforce on the rear axle was maximized and decreased on the front.
To achieve the former, front wings' AoA was decreased, and an optimized rear wing (new leading edge), coupled with new winglets, was introduced. However, the main update involved the undertray bodywork with a brand new diffuser.

Once again, the most interesting element to analyze is the diffuser itself: this time a double stage diffuser was used. It's been designed for two main functions: maximize the extraction volume and separate into two stages the management of the vortices.

(here you see the primordial version of that concept, the one used in the race...not very effective, but very promising)

While the first function implies a simple development path (the only worry is about not stalling the diffuser, i.e. optimizing the AoA), the second development stage, concerning vortices, requires much time to spend...time that i did not have, as the overall decrease of performance from this race clearly attests...time that could have been spent to significantly increase downforce with a minimum drag penalty.

Here you can see a couple of interacting vortices from an old (relatively, as it's just days old) iteration of my diffuser. Two strong, effective vortices boosting airflow extraction even in this chaotic environment (latest iterations present a much more complex system of vortices yet a more ordered environment):

[variante]

Here's a new shade of Livore.

After not being able to repeate the same performance, in race 2 and 3, of the first race due to CFD correlation problems (despite the introduction of a very interesting diffuser concept and the optimization of vortex management, as you can see here: http://s1372.photobucket.com/user/joreh ... 8.png.html), a new car is introduced to face the last half of the championship.

The regulations have changed quite a lot, and the remaining three tracks require high efficiency setups: necessities that gave life -unfortunately in a very brief time- to the new Livore. While not the most beautiful Variante racer, it is by far the one with the lowest drag and highest efficiency.







I would advise my competitors against copying this layout believing that's the best possible...it was, indeed, developed without testing other configurations (such as current LMP,...)!! Also, I would like to underline the obvious: this is just a showcar...similar to the actual thing, but different in some key areas.

Anyway, due to a lack of time i have during this period, this car will hardly be updated anymore. I wouldn't have brought into play any car at all if i hadn't believed that at least the podium is a realistic target with the new, underdeveloped machine.

Let's hope for the best! Any question welcomed!

[RicME85]

It's like an Enzo

[CAEdevice]

Wonderful! I guess some numbers: dr=1500N, df=7500N... maybe?

[machin]

Interesting..... very interesting......

[LVDH]

A no rear wing concept. Looks very clean and sleek. In a few days we will know more.

[graham.reeds]

I was trying to do something similar but I didn't taper the rear like you did. Also my drivers windscreen is encroaching on the visibility area but since its just the windscreen.

My biggest problem is lack of skill not ideas!