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Raising Arizona said:
As I watched the Rolex 24 this past weekend all the DP (prototype) cars had the square'd off backends as discussed above. Very unfinished, very racey looking, which I like. Looking at the GT2 and GT3 cars, there stock and round (RX-8, F430, 911, etc. and appear to run the track just fine. There's nothing square about a 911.

I think a lot of the issue is that the rules dictate what they can do to the body. A few years back touring cars were the pinnacle of aero design on production based cars. But to reduce out of hand development costs, they restricted what you could do to the body panels. That is why BTCC cars run very little aero stuff, they did allow basic things like uselessly small wings just to give the cars a racy look for the fans, but otherwise they are basic.
Now look at the DTM series. Totally different look to the cars.
http://speedhunters.com/archive/2008/07/31/gallery-gt-gt-nurburgring-dtm-race.aspx
 

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Bill Strong said:
I think a lot of the issue is that the rules dictate what they can do to the body. A few years back touring cars were the pinnacle of aero design on production based cars. But to reduce out of hand development costs, they restricted what you could do to the body panels. That is why BTCC cars run very little aero stuff, they did allow basic things like uselessly small wings just to give the cars a racy look for the fans, but otherwise they are basic.
Now look at the DTM series. Totally different look to the cars.
http://speedhunters.com/archive/2008/07/31/gallery-gt-gt-nurburgring-dtm-race.aspx
watch the DTM's and BTCC alot and your very right. The DTM's have all those rear aero's going from the rear fender to the back and rear diffuser, actually the entire car. I'd love to buy a C300 sport and trick it out like that. Love'm....anyway, I'm really looking forward to testing my rear diffuser/vert TMIC. Should be intersting to see if my guessing actually works. Hmmmmmm :eek:
 

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Couple thoughts:
~How difficult would it be to seal the area under the radiator with underbody panels and redirect the air originally flowing downward to the front wheel brake area via air ducts?
-Would that create an airflow bottleneck at the radiator?

~The low pressure area that forms behind the rear glass could be improved with a downward spoiler near the third brake light to make the air flow smoothly down over the engine lid instead of forming vortexes. Think of the SUVs and hatchbacks that have spoilers over the hatchback glass to direct air down the back of the car.
Seems like the only other option is louvers or some kind of sloping hatch.
 

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Your studies of the radiator area interest me. Air sems to enter the cavity and then bottle up behind the radiator before being pushed out under the car. This would seem to cause lift.

Instead of venting air out of the top, what if you diverted the air to the sides (add a lower air dam). This would create a negative air pressure under the radiator, increase downforce, and draw air through the radiator.

I am no expert on fluid dynamics, so excuse me if I am out in left field.

I am surprised to see drag coefficient at .36. With it's low profile and smallish frontal area I would expect better. It seems like we should be closer to the magic number of .29.

Your studies are great by the way, keep up the good work.
 

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I need to get Solid works.
I need to see what massive reduction this yields.


Radiator butted up against firewall.
hole behind radiator cut out.
Ducting made behind radiator to vent out of the hood (drift style hood)
Ducting made with the bumper to prevent air from going anywhere but through the radiator (simple task all of these)
Flat underbody from the front back to the engine bay.
NACA Ducts for the engine bay.
Rear Diffuser with flat center and vortex tunnels on either side of the car (bout 8-10 inch wide each)
Mini vortex tunnel with deflectors in front of front tires.
Deflectors (think ferarri) for rear tires (with and without)
Fastback lid, removed stock wing, and put VOLTEX wing at roof line level.
Then with and without vortex generators at the start of the fastback.

Vortex tunnels to be at 10 degrees.
*vortex generators required for anything greater than 14 degrees of angle of attack.
 

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What a great body of work!

I was wondering if a pair of big SPAL puller fans behind the radiator in a "border hood" configuration would assist, because you're "creating" a lower pressure area/more porous surface by the action of the fan than if you were to rely on airflow alone. I understand that there will be a "stall" speed as the fans will only work to a certain point, but I don't think we need to model airspeed much higher than 150 knots, right?

It is good to know the reduction in velocity and flow through there though, reducing front end lift is always a good thing!

Keep up the fantastic work.

Cheers,
Will
 

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Discussion Starter #71
OK, I haven't forgotten this project, just busy and got a little bogged down in trying to improve my radiator model. I think I have it much closer to reality now, and I have updated the numbers and images in my earlier posts to reflect the new results.

Basically, I finally found some radiator flow data here http://www.supraforums.com/forum/archive/index.php/t-581479.html and tried to modify my model to at least somewhat reflect that. I don't know how accurate that data is, but its better than the nothing I was working with before. I also think my radiator is now more accurate, since as you will notice it now shows a pressure drop from one side to the other and a much lower velocity through the radiator.

The biggest effects of these changes has been a pretty significant reduction in drag (actually, its much closer to what you would expect at this point), as well as larger differences between the various configurations.
 

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Discussion Starter #72 (Edited)
Here I experimented with what I am calling a "corvette style" air dam, since that's where you tend to see them. Basically, a small flap under the car, running all the way across, in the area of the front wheels.




This configuration produced an increase of lift to 52lb, which is 10lb more than the Holy lip configuration that it was based on. Drag was reduced slightly to .301, compared to .315 with the basic Holy lip setup.
 

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Discussion Starter #73 (Edited)
Next, I tried what I am calling a "race" air dam, since you tend to see this sort of vertical sheet metal air dam on autocross cars and other amateur budget race car sort of application. This actually increased lift again, to 66lb, but reduced drag quite significantly to .285.


 

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Discussion Starter #74 (Edited)
Here I combined the border style vented hood and sealed front underbody with the previous "race" air dam configuration. I must admit, this one surprises me a little, and I don't really see anything in the pressure plots to support the numbers. On the other hand, the numbers were produced in exactly the same way as all the others, so they should be consistent.

Lift was massively increased to 111lb, and drag was also increased to .331.


 

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Discussion Starter #75 (Edited)
Just for fun, I ran one with the windows down and the T-Tops off. Otherwise this is the same as the Holy lip configuration. Unless otherwise mentioned, that is my baseline, since that is how my car is currently configured. Lift was 59lb, and drag was .365. Note that the airflow separates from the roof of the car quite badly with the tops off and the high pressure zone normally found above the spoiler is completely eliminated.


 

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Discussion Starter #76 (Edited)
Finally, I ran a test with the stock spoiler removed. Lift was 46.7lb, compared to 42.7lb with the spoiler, and drag was .299 compared to .315 with.


 

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misut0 said:
I think somebody mentioned it earlier, but the chicken wire would work. You can get that at your local Home Depot.
No-no, I'll find a large piece of grill like material and cut to fit. It has to look good too. this will surround the bottom of the bumper to the rear diffuser so the IC will be behind it.
 

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Raising Arizona said:
I should send you my rear diffuser and you can hook that up and test it out.
From what I understand and have read a rear diffuser won't do anything unless you have sealed underneath your engine bay completely.
 
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