Internal Body Aerodynamics

I saw that car probably 5-6 years ago at NJ Motorsports Park... Cool guy and wild car (although he wasnt running the car) Love all the carbon work... especially the rear diffusor. I question the side scoops drag vs benefit though. For 20K someone is going to get a hell of a car
 
Picked up another book...

These are from Thomas D. Gillespe's Fundamentals of Vehicle Dynamics.

He uses a transverse mounted engine for the bay drag discussion - I'll see if I can find some streamlines from the B-B and C-C cutaway planes:
12695cc4c9bab32ba.jpg
[Maybe some SAE members here can chase down the reference for us?]
NOTE: The diagram does raise the importance of sealing the radiator to keep flow moving along and not "circling back" or becoming cross flow.

And here is another look at the flow in a wheel well:
12695cc4c9ba991a4.jpg

The diagram does lend credence to using the gills or fender louvers to evacuate the wheel well.

Cheers - Jim
 
vette427sbc said:
There are metal plates that bolt to the bottom of the fenders and tie them to the bottom of the wheel well... mine (stock?) were steel. Easily replicated in aluminum :amused:
Click to expand...

I pulled out the 14 oz steel units and replaced them with 6 oz aluminum pieces. I mounted the sheets at the bottom edge of the frame to help reduce some of the turbulence behind the lower wheel wells.
 
Good weight savings there.

Project for "just weight" or planning some under hood aero?
Is it open to the wheel well or closed as original?
Are you planning a duct to the gills too?

Cheers - Jim
 
phantomjock said:
Good weight savings there.

Project for "just weight" or planning some under hood aero? Both. I also moved the location of that lightened panel.
Is it open to the wheel well or closed as original? Closed
Are you planning a duct to the gills too? No. I'm trying not to cut up any of the bodywork anywhere.

Cheers - Jim
Click to expand...

I don't know if my experience with the front wheel well air is similar or different than diagram 4.15. My pace car front air dam seems to divert a decent amount of air sideways, and the brake pad dust is definitely making its way outward, so some wheel well air is obviously moving laterally outward, but given how dirty the wheels become from this dust I could be convinced that there is some air separation going on, causing the dust to cloud up near the wheel outer surface. Just speculation on my part, I don't know right off on a good way to measure or confirm it.
 
69427 said:
phantomjock said:
Good weight savings there.

Project for "just weight" or planning some under hood aero? Both. I also moved the location of that lightened panel.
Is it open to the wheel well or closed as original? Closed
Are you planning a duct to the gills too? No. I'm trying not to cut up any of the bodywork anywhere.

Cheers - Jim
Click to expand...

I don't know if my experience with the front wheel well air is similar or different than diagram 4.15. My pace car front air dam seems to divert a decent amount of air sideways, and the brake pad dust is definitely making its way outward, so some wheel well air is obviously moving laterally outward, but given how dirty the wheels become from this dust I could be convinced that there is some air separation going on, causing the dust to cloud up near the wheel outer surface. Just speculation on my part, I don't know right off on a good way to measure or confirm it.
Click to expand...

Here is something you can take as tested gospel. The vents above the wheel on the Viper ACR WILL NOT extract air from the wheel well when the louvers are installed. The air is wrapping around the wheel in the direction of rotation and it cannot make the 135 degree turn to exit the louvers. I have tested it with yarn tufts to 150 mph. The same is true of the backwards facing scoops on a 69 Dodge Daytona Charger (when they are opened to the wheelwell). We tested that with ink drops on a Bonneville Salt Flat car. BUT, when you take the louvers out of the hole in the ACR fender, air, pieces of rubber, birds, and small children are expelled straight up out the hole and you can feel the increase in downforce. Also note the two canards in front of the wheel well - they have lips on their outer edge that act as vortex generators and create a low pressure area just outside of the tire. This pulls some air out of the wheelwell and through the wheels past the brakes (good for cooling). The spats on a late Corvette do a little of the same as they create a little bit of low pressure outside of the wheel.

Pappy

Viper Vent 1.jpg

Viper Vent 2.jpg
 
Pappy -

It's great to have "real-life" info like you've passed along. I can say from my experience (on the sports racer) there was a noted difference pre and post louvers.

This season, I'll be capturing "real" data to verify. Plan includes A-B testing with louvers, open - and filled. Video and data if I'm really prepared. Tuft testing looks best on video, and less messy than ink/oil-dye streak testing, even if it perturbs the near-field flow.

I note the LMP cars have all migrated to the open fender in lieu of louvers. I had understood it was in an effort to keep them from going airborne when traveling backwards following a spin.

End plates are - and have - undergone a huge amount of engineering for that last 1/10 percent. All seems to have been in the direction which you mentioned, and 69427 has noted, generate a pressure differential. This is most noted in open wheel (F1) as they try and create an Air Fender to reduce wheel/tire drag. Vortex generation efforts can be effective this way and in creating a curtain as we saw in some of the earlier posts.

Back to rebuilding carbs.

Cheers - Jim
 
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“BUT, when you take the louvers out of the hole in the ACR fender, air, pieces of rubber, birds, and small children are expelled straight up out the hole and you can feel the increase in downforce. “

Very graphic description, ACR’s are bad ass cars. Always wanted one.

Duntov sells Corvette louvres with the gills going up above the fender. They each create a low pressure zone.

“The louvers mount up and into the wind stream, and are open at the back. This aids evacuation of hot air from the engine compartment. ”

http://www.duntovmotors.com/vintage-racing-parts-body.php

A backward facing step has been well studied and is sort of analogous to these louvers. It has a low pressure region. Google has lots of plots of the pres distribution if anyone is interested.
 
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Has anyone done pressure testing on the raised L88 hoods? I am wanting to reduce lift and help vent under hood temp and pressure with this hood. I read the thread and saw the holes cut in hoods before the buldge here
L88h1.jpg
it vents his pressure. With a hood like this
H1291_73_82_Corvette_L88_bolt_on_Hood_1.jpg
wouldnt this casue a high pressure area and push more air back in the vents?
 
My suspicion is (and testing would help - or looking for someone's results)- is that the "uplift" on the hood would act as a gurney-like flap and create a low pressure zone there, just ahead of the windshield, where there is a huge high pressure zone. Sorry, but I haven't seen this testing done on this configuration, smoke, streak, or tuft, let alone wind tunnel. If I come across some documentation I'll bring it on. There was some testing similar on the earlier Grand Sports hood louvers, I'll look for that, and see if there is an analogy.

Sorry, that is a long way to say, maybe - but maybe not. I believe those "should" evacuate air from under hood (and some heat). My radiator on the SR "dumps" like that, minus the grills.

Other examples; Ford GT-40 -- original and new, Factory 5 GTM, many variants of the Ferrari, etc. These analogs make me suspect, reverse flow would be very unlikely on the hood.

Cheers - Jim
 
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Kacyc3 said:
Has anyone done pressure testing on the raised L88 hoods? I am wanting to reduce lift and help vent under hood temp and pressure with this hood. I read the thread and saw the holes cut in hoods before the buldge here

wouldnt this casue a high pressure area and push more air back in the vents?
Click to expand...

I opened those up 10 years ago, it helped a bit to keep under hood temps down. Two biggest improvements I made were a pusher fan in front of the rad and a return flow pressure regulator on the fuel lines by the carb. I was having vapor lock issues.
 
Aston Martin has gone all in on big diffusers ( hold our beer ...). I like the rear tires exposed from the back.


[ame]https://www.youtube.com/watch?v=4mh9Rl7Gips[/ame]

Phantomjock, there are the high exhaust outlets you mentioned earlier.
 
[ame]https://www.youtube.com/watch?v=1r4oQvG1m2c[/ame]

20 side mirror design iterations. Pretty interesting talk by Hennessy.
 
Mirrors are so "Old Skool!" :amazed:

I'm a bit surprised to not see an array of cameras and a threat warning/proximity system that "calls" for you attention. Less drag too, and what the heck, when you loose power the ecu/brain quits and you stop.

Cheers - Jim
 
A nice section showing aero detail after the 5 minute mark.

[ame]https://www.youtube.com/watch?v=wjJKg8-dsI0&app=desktop[/ame]
 
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