Formula Vee CFD???

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GTRdesign
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Joined: Mon Oct 20, 2008 10:30 am
Location: Pretoria, South Africa

Formula Vee CFD???

Postby GTRdesign » Sun Apr 11, 2010 11:20 am

Hey there guys!

I'm currently building a Formula Vee car here in South Africa. It's a really competitive series with all the cars locally designed and built by guys in their garages. Check out http://www.formulaveesa.org.za to find out more.

I've been designing the car in Pro-E for the last 2 years or so and have finally started construction, with the chassis nearly complete. However, I've never had a chance to run the car through CFD.

Would anyone be interested in running it? would be quite cool to be able to compare theory and practice as it's a real car that will compete in a national championship, and changes etc... can be measure in the real world.

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regards,
If you can't fix it with a hammer, it's probably electrical

Giblet
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Joined: Mon Mar 19, 2007 12:47 am
Location: Downtown Canada

Re: Formula Vee CFD???

Postby Giblet » Sun Apr 11, 2010 12:40 pm

Fixed Images for you.

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Before I do anything I ask myself “Would an idiot do that?” And if the answer is yes, I do not do that thing. - Dwight Schrute

tomislavp4
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Joined: Fri Jun 16, 2006 4:07 pm
Location: Sweden & The Republic of Macedonia

Re: Formula Vee CFD???

Postby tomislavp4 » Sun Apr 11, 2010 1:08 pm

That is a nice looking racer there =D> I really like it and I hope that someone will be willing to do some CFD on it, it would be cool to see the development :)

BreezyRacer
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Joined: Fri Nov 03, 2006 11:31 pm

Re: Formula Vee CFD???

Postby BreezyRacer » Sun Apr 11, 2010 3:36 pm

You're way too late doing the CFD AFTER you design it.

Do you have to use a beam axle? They are pretty draggy.

Every once in a while Racecar Engineering does some aero and chassis stuff on Vees, if you're not familiar with it, check it out. Those Vees are nothing like what you're building though .. they are traditional Vees with flat 4 cyl air cooled engines.

One last thing .. how you gonna get that transaxle above the diffuser?

GTRdesign
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Joined: Mon Oct 20, 2008 10:30 am
Location: Pretoria, South Africa

Re: Formula Vee CFD???

Postby GTRdesign » Mon Apr 12, 2010 10:23 am

Thanks guys!!!

The foundations are obviously set, but much development in the detail of the body can still be done. I'm hoping to have the first one ready in the next couple of months and then to start track development work on it before debut for next years championship. At the same time I'd like to pick some of the minds on this forum to see what we can achieve. I'd like to take some of your ideas, implement them, and then report back on their results.

The beam is mandatory, and an area of concern as we're not allowed to use fairings. It's the main point of interest for me in a CFD analysis. Some of the ideas I'd like to explore to negate it's effect on the car's airflow are:

1) Locally modifying the Reynolds number by increasing the surface roughness of beam's surface. (i.e. bonding large grain grit to the surface or something like that) or... mounting a vertical fence on the beam an inch or so off the body.

2) strategic placement of vortex generators to try and keep the boundary layer attached to the body aft of the beam.

3) To see the interaction between the beam and the splitter, and if there's anything that can be done in the splitter/floor area to negate that.

Just a few ideas so far, but hopefully more will come out of this.

As for a diffuser, there is some space under the beetle gearbox, but we're only allowed a 8mm plywood plank under the car with curvature in one direction. We can place gurney tabs. The profile of the floor is free.
If you can't fix it with a hammer, it's probably electrical

autogyro
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Joined: Sun Oct 04, 2009 2:03 pm

Re: Formula Vee CFD???

Postby autogyro » Mon Apr 12, 2010 10:57 am

Why not encase the beams with an aerofoil section and create more DF.
At the rear the DF from aero beam sections would be unsprung so you could reduce diffuser need and use softer rear springs.

BreezyRacer
2
Joined: Fri Nov 03, 2006 11:31 pm

Re: Formula Vee CFD???

Postby BreezyRacer » Mon Apr 12, 2010 12:59 pm

Running a full CFD just for playing with surface roughness is not a good idea, as CFD really has a difficult time with very subtle analysis like you're taking about. If you're playing with tack ons to reduce drag (VG's and surface roughness) I would try to do some coast down testing instead, and of course that can all happen after the build.

An aero question I have though .. why is the nose drooped down to the track level? As a ballast location? From an aero standpoint I would be looking to make sure the nose doesn't dirty up the air. That current nose disrupts the airflow from the track level to top of the body. If you keep the nose up the front of the chassis and sidepods will have clean air. Aero starts at the front of the car ..

One more thing .. the splitter in front of the sidepods is likely needing to be extended further forward .. maybe something like 75-100 mm more or so. Splitters isolate bodywork aero from under tray aero.

Are you allowed to run a diffuser with sides or is the single curve rule valid from the nose to the tail? If that rule is just between axles we can do a lot more with the back of the car. A flatish panel like yo have now is largely a drag reducer now, which is good, but a true diffuser can do that plus add DF.

GTRdesign
2
Joined: Mon Oct 20, 2008 10:30 am
Location: Pretoria, South Africa

Re: Formula Vee CFD???

Postby GTRdesign » Thu Apr 15, 2010 12:31 pm

Thanks for the comments!!!

My thinking with the drooped nose was to try and develop some down force with it, as we're not allowed wings (also a great place for some ballast). Did I go the wrong way? I have a second high, slim nose for the vehicle for long tracks. Perhaps we can compare them?

As for diffusers, curve in single plane only unfortunately, full length of vehicle, but I have thought of doing a double deck floor, i.e. two floors, the rear one starting behind the upturned end of a forward one. I think I'll manage to get that through the single plane curvature rule. Don't know if it'll be worth the fight though.

Autogyro, unfortunately no aero sections allowed on any of the beams, pity, cause that would've been really cool!
If you can't fix it with a hammer, it's probably electrical

BreezyRacer
2
Joined: Fri Nov 03, 2006 11:31 pm

Re: Formula Vee CFD???

Postby BreezyRacer » Thu Apr 15, 2010 12:42 pm

It sounds like maybe you've raced these cars for some time. What are the chassis limitations/problems with them? What end is the limited end? I would suspect the front end but it's really a track and speed dependent thing. If we can understand the inherit limitations of these chassis, the best thing would be to focus on that problem area.

And how much ballast weight do you have to play with? Are the tires speced out and are rims sizes mandated?

If the front is the problem there are a few options for generations some downforce.

marcush.
268
Joined: Tue Mar 09, 2004 3:55 pm

Re: Formula Vee CFD???

Postby marcush. » Thu Apr 15, 2010 2:12 pm

would it be feasible to put the air inlet for the coolers in between the two beams of the front axle?
that way the obstruction of the beam would make sense at least ,and in designing the watercooler ducting /sidepods to shadow the beam the real cross section of the car might not even increase...

GTRdesign
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Joined: Mon Oct 20, 2008 10:30 am
Location: Pretoria, South Africa

Re: Formula Vee CFD???

Postby GTRdesign » Thu Apr 15, 2010 3:45 pm

Yeah, this will be my 3rd car! all scratch built!

I have about 20kg of ballast to play with, of which I want to put much into the nose. We've recently changed our control tire, with a wider front, thus I want to move some of the mechanical load forward.

Aerodynamically, I'd like to first ascertain if we are producing any DF, at this point I doubt it, perhaps the cars are slightly negative lift. Areas's I'd like to generate some DF, compared to the other cars, are with my sidepods and drooped nose. But at this point it's so so theoretical.

Some of the interesting things about Vee's are:

Rear: We use a zero roll setup at the back with one coil-over. reason for this is a very high RC at the back because of the mandatory swing axle VW type 1 gearbox. We use a very stiff rear spring with very little camber, as adding camber dramatically increases driveline drag. (The joints are not CV)

Front: Mandatory VW type 1 trailing arm suspension. RC consequently at ground level. I like a soft front end with enough preload so I can lift the inner wheel over curbs. I also run some anti-dive, with a 3rd spring at the longer tracks.

Motor: Stock 1400 watercooled golf motor, with a control cam, and 40mm twin sidedraughts. everyone has very similar power which makes for nice tight racing. Focus really is on chassis, suspension and driver.

Even with our fairly limited "technology", we match Formula Ford Zetec times, especially at tight twisty tracks.
If you can't fix it with a hammer, it's probably electrical

marcush.
268
Joined: Tue Mar 09, 2004 3:55 pm

Re: Formula Vee CFD???

Postby marcush. » Thu Apr 15, 2010 3:53 pm

I saw in the regs that your minimum weight is 520 kilos whereas in europe there is 390 kg (but without driver..)

so where are those 40-50 kilos to be found..or are the europeans all running overweight,or maybe the Type 1 engine is this much lighter ,as it is still allowed in europe?

GTRdesign
2
Joined: Mon Oct 20, 2008 10:30 am
Location: Pretoria, South Africa

Re: Formula Vee CFD???

Postby GTRdesign » Thu Apr 15, 2010 4:18 pm

Yip, our minimum dry weight is 420kg without driver and fuel, so about 30kg. the type one engine is definitely lighter, with a much lower cg, and doesn't need heavy radiators filled with water. Our rules were the same as the Europeans until the early 90's when type 1 motors started to get scarce and expensive, so they simply changed to water-cooled and adjusted the weight. Many of the original water-cooled cars were simply air-cooled vehicles with new motors.

I believe in Germany they are now using a 1300 water-cooled 8v crossflow motor.
If you can't fix it with a hammer, it's probably electrical

BreezyRacer
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Joined: Fri Nov 03, 2006 11:31 pm

Re: Formula Vee CFD???

Postby BreezyRacer » Thu Apr 15, 2010 5:36 pm

Yes, in my day I've played with VW and zero roll and z bars, etc. The zero roll systems I played with were so over levered that you got very little shock action vs wheel travel. That was a problem we had to fight quite a bit, as was droop travel. That was one sensitive little chassis. When you got it right it was respectable but keeping it there was a chore.

If you're looking to add front DF, I would raise the nose and move the chassis bodywork forward, with a Vee split off to each side running into your radiator cooling. Then I would extend a splitter across the front of the chassis, protruding probably 150-200mm at the middle and maybe 150 mm or more in front of the sidepods. The high pressure airflow at the bodywork will build onto the splitter, making good dependable DF and isolating undertray airflow as well, reducing drag, and maybe even creating some DF of it's own with the undertray.

If you wanted to, you could actually extend the center of the splitter to house your ballast. It would be a good location. I would even build the splitter so you could slide and lock ballast in any position from the driver's butt to the front of the splitter. And if you're sure you want to ballast to the front of the car, move the rads further towards the front too.

You won't gain much if any DF from the nose .. mostly just create turbulent flow that washes back to the chassis.

engineguru00
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Location: Buffalo,NY

Re: Formula Vee CFD???

Postby engineguru00 » Fri Apr 16, 2010 12:56 am

I am currently running CFD for GTR on the project and hopefully we will have some numbers/pictures in the next day or so. I did notice a few things when looking at the model though (alot easier when you can rotate it). The sidepod exits lie directly inline with the lower beams of the front axle, which could cause some issues cooling wise but my guess is the cooling system is over sized.

My time as an engine guy also gives me a few concerns on the ram air plenum that I saw. Be careful with the pressure distribution across the system as it runs on the track, its likely the rear cylinders will be drawing from much higher pressure than the fronts and this difference in pressure will change with track speed. Is this engine carbed or EFI? Nice thing about carbs is they self regulate in this case, where as EFI wont automatically unless you run a closed loop correction system on every cylinder individually.
Chris
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