Internal Body Aerodynamics

In lieu of another cuppa'

Chris -

You have had "Eyes-On" these vanes, so maybe you could verify/correct my best guess at their size? I've made my estimate by assuming the bolt heads are about 1/2"/13mm. Do my numbers even look close?



I'm interested as I am just now working a plan to incorporate on my SR as a test (mule) to try out. I've made a smallish splitter and could test each in sequence if I have the time. Meanwhile, I'll wait for your ideas on the size.

I'm thinking of making a pair of plates to secure some rubberized edging (you know - from the big box racing supply store).

Thanks.

Cheers - JIm

Put me down for a "Thank You, Chris" also. :thumbs:

My goal, as I've stated in the past, is to reduce aero lift and improve the tire grip of my antique, while retaining a stock look when possible. My car is so close to stock appearance that rarely at track days do any (later model) Corvette drivers give my car a second glance. But frequently, after the first or second session, I'm visited by inquiring minds as to why my 50 year old car is filling their mirrors. I don't need to have my self-esteem pumped up by strangers, but I willing admit the inquiries about my car do give me a bit of engineering satisfaction. :wink:

phantomjock said:

Chris -

You have had "Eyes-On" these vanes, so maybe you could verify/correct my best guess at their size? I've made my estimate by assuming the bolt heads are about 1/2"/13mm. Do my numbers even look close?



I'm interested as I am just now working a plan to incorporate on my SR as a test (mule) to try out. I've made a smallish splitter and could test each in sequence if I have the time. Meanwhile, I'll wait for your ideas on the size.

I'm thinking of making a pair of plates to secure some rubberized edging (you know - from the big box racing supply store).

Thanks.

Cheers - JIm

Click to expand...

Let us know what you find. I'm still trying to figure out if the vanes are there to even out/distribute the air mass under the vehicle floor, or if it is there to divert a portion of the air mass out the lower pressure(?) front wheelwell.

Which, gives me some incentive to measure the relative/differential pressures of under my car and the wheelwell area. Theoretically, my front wheelwells should have a slight low pressure, as the front pace car spoiler directs the side-fender air outward/laterally, pulling air out of the wheelwell volume. Given how dirty my wheels get from brake dust after a day at the track, I have to believe that the general direction of the wheelwell air flow is from undercar to outside the car.

Happy to contribute what I can!
Jim, I’d say your numbers are close to what I would have guessed they were.
Not knowing much about how the air is supposed to flow under these cars, I’d say the vanes were designed to direct air out just behind the front wheel, not into it

69427 said:

Let us know what you find. I'm still trying to figure out if the vanes are there to even out/distribute the air mass under the vehicle floor, or if it is there to divert a portion of the air mass out the lower pressure(?) front wheelwell.

Which, gives me some incentive to measure the relative/differential pressures of under my car and the wheelwell area. Theoretically, my front wheelwells should have a slight low pressure, as the front pace car spoiler directs the side-fender air outward/laterally, pulling air out of the wheelwell volume. Given how dirty my wheels get from brake dust after a day at the track, I have to believe that the general direction of the wheelwell air flow is from undercar to outside the car.

Click to expand...

That is so cool you're filling their mirrors! Now get to PASSING!


I've found a CFD plot of before and after the vanes added. I can't speak to its "creds" but looks better than my "phony airstream plots" a few pages back!



Top one is before vanes and lower with vanes - car nose is on the right - per the previous plots.

Very obvious with the vanes even showing up in the plot. They are clearly directing the air out behind the wheels. I'm not seeing the "Huge" deltas that were in the images I posted of the centerline pressures. Definitely some, and when I look at it some more - there is a change - but over a large area. Surprising the center area just forward of the rear wheels shows some good increase in low pressure too.

69427 - I'd say you are correct looking at this plot of the -no vane CFD, the pressure differential is showing what you have seen trackside, air flowing outwards. Now, I suggest that these ideas have very good opportunities for use on our "antiques." The underbody CFD is not so significantly different from what a C3 could be - but first gotta clean up all that "STUFF." Like add a full belly pan, sort out cooling, a few stealth areo underbody mods - hey you'll be passing them in no time! And they say, "WTF??!!" Yes, the outflow mid body from the big rear facing exit contributes a lot, but centerline and vane mod - do-able.

This has been fun and inspiring. Thanks Guys. And, (scotch in hand), Cheers - Jim

YouTube keeps recommending videos. Lots of extra features.

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

Inspired by Pappy’s post about the airflow around the oil tank having a notable effect on oil temps got me (and Bob!) thinking...

In my own car, my oil tank sits right next to an “unused” duct from the wheel well to evacuate air out the side gills. My idea was to use the side of the tank as one of the walls of the duct with some aluminum fins welded to the tank to act as a heat sink.

An article I found, with some good info on “forced convection”
It’s fairly short but provides a good starting point for optimizing emissivity, boundary layers and fin density.

https://www.digikey.com/Site/Global/Layouts/DownloadPdf.ashx?pdfUrl=F51974C9A6D544F1A7D8F119514B67FF

Noteworthy points in the article:
Black3 anodizing brings up emissivity considerably, but mostly in natural convection situations

Boundary airflow is a big killer for fin efficiency, turbulence between the fins (to an extent) is more desired

Assuming most of us are using aluminum, 6063 has a slightly higher conductivity compared to 6061

One of the OEM applications I’ve seen use heat sinks is on BMW rear diff housings. Not sure if it’s an ///M car only thing but I’ll see if I can get some pictures of the next one that comes in

Adding external fins also doesn’t add pressure drop/loss like you would get from an air to oil heat exchanger.

More big $$$$$ cars. But, if you want to see new aero, they are the cars to look at.

[ame]https://www.youtube.com/watch?v=TTObTPzRN6s[/ame]

In my own car, my oil tank sits right next to an “unused” duct from the wheel well to evacuate air out the side gills. My idea was to use the side of the tank as one of the walls of the duct with some aluminum fins welded to the tank to act as a heat sink.

Click to expand...

Kinda', sorta" like this with some fins on the duct?:


That seems like a great idea. I guess the fins would be inside the duct to evacuate the heat out as well. One word -- COOL.

Do you have a diagram of how the duct fits in the bay? Intake from bottom - or the bay itself? I like it. Might use it. Two sides - oil cooler on one, transmission cooler on the other. Aluminum sheet - or fiberglass duct? You know me - and what I'll use.

Cheers - Jim

It’s not built yet, but the plan is to have a large opening in the back of the wheel well that is ducted out the side gill. “Free” high pressure ambient temperature air. Drivers side will have the oil cooler in it, but I wasn’t able to package any cooler in the passenger side because the oil tank takes up most of the optimal real estate. Carbon is my proposed material... we’ll see how it goes...

I’ll start with revisiting the Underbody Strake/Vanes.
Here is a nice example of the Mercedes Air curtain and it shows the flow field associated with them installed. With some tailoring it could be used to create flow in the location you'd want. Seems a lot easier than creating ductwork (with the attendant internal drag) doesn’t it?



Now (staying in Germany), the Porsche 918 active Aero approach to these vanes:


Note the flap is up – or down as needed. I don’t know if operated manually, by temperature, or simply a “Performance Switch.” Hey for near a million bucks for the car it ought to be pretty cool.

Well, it is. I note they also have implemented a cooling/drag reduction set of louvers/doors for the intakes in the nose. Something I recall being discussed here sometime back as an option for the C3. Should be pretty easy.



But back in the Good Old USA – we will not be left behind! The following are from a GM patent:


And the side view for splitter Active Aero and the hood cooling vanes:

Of course, these all work best with a smooth underbody. But in any case, there is lots of opportunity to “shape up” the Old Girls!

Cheers - Jim

I've been following and considering Active Aero for some time. You'll recall my fascination with the Chaparral cars. I'll start a separate thread in a few days.

vette427sbc said:

Inspired by Pappy’s post about the airflow around the oil tank having a notable effect on oil temps got me (and Bob!) thinking...

In my own car, my oil tank sits right next to an “unused” duct from the wheel well to evacuate air out the side gills. My idea was to use the side of the tank as one of the walls of the duct with some aluminum fins welded to the tank to act as a heat sink.

An article I found, with some good info on “forced convection”
It’s fairly short but provides a good starting point for optimizing emissivity, boundary layers and fin density.

https://www.digikey.com/Site/Global/Layouts/DownloadPdf.ashx?pdfUrl=F51974C9A6D544F1A7D8F119514B67FF

Noteworthy points in the article:
Black3 anodizing brings up emissivity considerably, but mostly in natural convection situations

Boundary airflow is a big killer for fin efficiency, turbulence between the fins (to an extent) is more desired

Assuming most of us are using aluminum, 6063 has a slightly higher conductivity compared to 6061

One of the OEM applications I’ve seen use heat sinks is on BMW rear diff housings. Not sure if it’s an ///M car only thing but I’ll see if I can get some pictures of the next one that comes in

Click to expand...

There are a lot of "apples-to-oranges" in the following observation, but kind-of interesting. My 2015 SS Camaro (LS3 w/8 qts of oil), C6 Z06 (dry sump w/ 10.5 qts), and Viper (11 qts) all use virtually the same liquid-to-liquid oil cooler - a finned aluminum unit. On the Camaro and Z06 the cooler is sandwiched between the engine block and catalytic converter - not much air flow and what there is is probably very hot. The Viper has the unit mounted forward of the engine and directly under one of the open hood vents. The Viper also has a large surface area, flat oil pan that is parallel to the ground and is almost at the same level as the front splitter and belly pan. It probably gets plenty of air flow across its surface. In town driving the Camaro's oil temp is around 225, the Z06 around 220, and the Viper 188-190 degrees. I have never seen over 228 on track in the Viper. I know, different motors and lots of other variables, but I always questioned why GM used a finned oil cooler stuck right next to the catalytic converter.

Pappy

vette427sbc said:

Inspired by Pappy’s post about the airflow around the oil tank having a notable effect on oil temps got me (and Bob!) thinking...

In my own car, my oil tank sits right next to an “unused” duct from the wheel well to evacuate air out the side gills. My idea was to use the side of the tank as one of the walls of the duct with some aluminum fins welded to the tank to act as a heat sink.

An article I found, with some good info on “forced convection”
It’s fairly short but provides a good starting point for optimizing emissivity, boundary layers and fin density.

https://www.digikey.com/Site/Global/Layouts/DownloadPdf.ashx?pdfUrl=F51974C9A6D544F1A7D8F119514B67FF

Noteworthy points in the article:
Black3 anodizing brings up emissivity considerably, but mostly in natural convection situations

Boundary airflow is a big killer for fin efficiency, turbulence between the fins (to an extent) is more desired

Assuming most of us are using aluminum, 6063 has a slightly higher conductivity compared to 6061

One of the OEM applications I’ve seen use heat sinks is on BMW rear diff housings. Not sure if it’s an ///M car only thing but I’ll see if I can get some pictures of the next one that comes in

Click to expand...

Thanks for the heatsink link. Looks interesting and practical (just skimmed through it at the moment). Page 4 caused me to chuckle. There's a diagram showing the commonality/analogy of heat flow and electrical current flow. My engineering experience is predominately electrical, and I've worked out a lot of designs/problems on my car by figuring out an electrical solution (changing current flow, voltage/pressure issues, capacitance/surge-volume affects, etc) and then converting that electrical solution to the mechanical analog on the car.

Perhaps not the most efficient way to do things, but that's how my brain is wired.

Every time I look at the batwing on my car, I always think about what additional gear lube cooling ability I could have done to the batwing if I had taken the time to weld a bunch of fins onto it. The stock batwing is certainly a better conductor of heat than the original cast iron cover, but it would be nice to pull some more heat out there, short of adding the complexity of a pump and heat exchanger.

69427 said:

.....Every time I look at the batwing on my car, I always think about what additional gear lube cooling ability I could have done to the batwing if I had taken the time to weld a bunch of fins onto it. The stock batwing is certainly a better conductor of heat than the original cast iron cover, but it would be nice to pull some more heat out there, short of adding the complexity of a pump and heat exchanger.

Click to expand...

I must have hours of searching in trying to find C4 road race guys that have issues with diff cooling (with no pump). I havent seen anyone mention a thing, which could be that, like you said, the batwing is such a large heatsink that it dissipates heat really well. I plan on collecting some temperature data on my stock C4 diff once I get the car on the road. Would be interesting to see any difference with a heatink ala the BMW diffs

vette427sbc said:

69427 said:

.....Every time I look at the batwing on my car, I always think about what additional gear lube cooling ability I could have done to the batwing if I had taken the time to weld a bunch of fins onto it. The stock batwing is certainly a better conductor of heat than the original cast iron cover, but it would be nice to pull some more heat out there, short of adding the complexity of a pump and heat exchanger.

Click to expand...

I must have hours of searching in trying to find C4 road race guys that have issues with diff cooling (with no pump). I havent seen anyone mention a thing, which could be that, like you said, the batwing is such a large heatsink that it dissipates heat really well. I plan on collecting some temperature data on my stock C4 diff once I get the car on the road. Would be interesting to see any difference with a heatink ala the BMW diffs

Click to expand...

FWIW I've never measured the actual gear lube temperature in my differential (I'm still using the C3 differential in front of the D36 batwing), but I've taken a few measurements of the batwing surfaces with my IR temperature gun. The cover area behind the ring gear, while the hottest, has never been hot enough that I considered sitting out a session to let it cool down. I credit that to several things: Breaks between the 15-20 minute sessions, no super long straights at WOT, and only a modest horsepower engine powering the drivetrain.

This is interesting. Basically he is making the spoked mag into a centrifugal compressor. Even though he says the opposite. Look at a centrifugal compressor disk if you want to see why. That does cool the brakes and does lower the pressure under the car, which explains why the wing needs less angle.



[ame]https://www.youtube.com/watch?v=dpje3x4s9U0[/ame]

This is obviously a well designed part, he just doesn’t have the facts straight.

“ Those wheel discs suck air from under the car, allowing the wing to use two degrees less rake to reduce drag and improve acceleration. These forces are balanced at the front by a splitter, new undertray, carbon floor, underbody aero curtains and a pair of canards on each side of the bumper”


https://www.whichcar.com.au/reviews/porsche-911-gt2-rs-mr-review

I've been trying for years to come up with a set of extraction fans for my track wheels, but haven't come up with anything that would seem to work well or package well. I'd sure love to be able to keep the rotors cooler and pull out some of the underhood and undercar air.

I haven't given up yet.

[ame]https://www.youtube.com/watch?v=piWgv60DTSY[/ame]