Internal Body Aerodynamics

[rtj]

Another car with the cut out front fender flares.

I’m increasing the fender flares on my junker 1.25 inches each side, might consider this for laughs.


[ame]https://www.youtube.com/watch?v=NrqNK7626BM&app=desktop[/ame]

 

[phantomjock]

I am not at the car just now - Sytill in Annapolis - preparing for a Blue Water Brokerage show. Hope to pass along our veerable saing home to new owners.

Meanwhile, that is what I plan to do with the rear of my front clip - at least the lower half. You can see how the splitter dam separates in the front, well the back of the fender will be cut away similarly.


A lot of the Speed Hunters do as well.

Cheers - Jim

 

[rtj]

Meanwhile, that is what I plan to do with the rear of my front clip - at least the lower half. You can see how the splitter dam separates in the front, well the back of the fender will be cut away similarly.


Cheers - Jim

It’s coming along! I see a lot of sanding in your future.

 

[rtj]

I was thinking, a c2 or c3 with sidepipe exhaust could run an L-shaped “heat shield” to get side skirt splitter effects.

If done right, might not look bad.

 

[rtj]

Mfain mentioned the C8R exhaust to blow above the diffuser to aid downforce.

This talks about a blown diffuser as creating boundary layer control, for an F1 this could mean above or inside the diffuser.

I think the c8r is more like a jet ejector effect, but lowering pressure at the exit lip would impact the boundary layer, but not like injection.

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

 

[69427]

External aero item

Not internal aero related, so I'll apologize right now, but this seems to be the thread that might get more input on my question/project. I'd like to put a small, as-non-obvious-as-possible aero mod to the area between my hood scoop and the windshield. My goal is to "stall" more air at the cowl area for several reasons. These reasons include a little more static pressure in that area for increased downforce on the center of the car, increased drag on the windshield to help slow the car when braking, and what the hell, the increased pressure behind the scoop opening might help the carb air intake quantity/mass a micro amount to help offset the increased drag of the aero setup.

Right now the easiest thing to do would be to remove the cowl grill strip, and replace it with a (painted) aluminum piece that has some tabs on it that would stall/spoil the air flow before it reaches the windshield.

I'm just beginning to kick around some ideas on the form of this thing, but any suggestions or caveats are welcomed.

 

[vette427sbc]

Not internal aero related, so I'll apologize right now, but this seems to be the thread that might get more input on my question/project. I'd like to put a small, as-non-obvious-as-possible aero mod to the area between my hood scoop and the windshield. My goal is to "stall" more air at the cowl area for several reasons. These reasons include a little more static pressure in that area for increased downforce on the center of the car, increased drag on the windshield to help slow the car when braking, and what the hell, the increased pressure behind the scoop opening might help the carb air intake quantity/mass a micro amount to help offset the increased drag of the aero setup.

Right now the easiest thing to do would be to remove the cowl grill strip, and replace it with a (painted) aluminum piece that has some tabs on it that would stall/spoil the air flow before it reaches the windshield.

I'm just beginning to kick around some ideas on the form of this thing, but any suggestions or caveats are welcomed.

Maybe not as effective as your tab idea, but Im thinking replace the grille with a metal piece that is smooth in the center (width of your cowl scoop) and then to the left and right of the cowl would be either open, or maybe have a recessed scoop to create some turbulence/downward pressure? A poorly designed NACA duct, if you will. That way you get to keep the footwell vents for those hot track days

 

[phantomjock]

Ok - I've been trying to get my head around the idea - see if I am close to understanding where you want to "stall" [I think you mean increase the pressure - or stagnate] the flow?

Here is some interesting work done on the C6 Racecars:

Note the hood is shaped to move the high pressure towards the A pillar --and off the windscreen.
Another view:


I couldn't find a CFD of a C3 so this volvo will have to do:


Some of the clear VGs available would be pretty unobtrusive to test out: https://www.aircraftspruce.com/cache/400-400-/catalog/graphics/05-04457.jpg Aircraft Spruce is the source.

 

[rtj]

I’ll throw this out, but may not be exactly right. Best hood scoop pressure for l88 by:

Replace wiper door with filler piece that seals to the windshield and the divider the wiper motor mounts on.

This will make the interior vents useless. Also, no more wipers.

Filler piece should be flush with hood or slightly below in the non-scoop region.

Put weather stripping on inside edge of hood to prevent flow.

Low restriction filter.

Clean out any lips or blockages inside the scoop.

 

[69427]

Ok - I've been trying to get my head around the idea - see if I am close to understanding where you want to "stall" [I think you mean increase the pressure - or stagnate] the flow?

Here is some interesting work done on the C6 Racecars:

Note the hood is shaped to move the high pressure towards the A pillar --and off the windscreen.
Another view:


I couldn't find a CFD of a C3 so this volvo will have to do:


Some of the clear VGs available would be pretty unobtrusive to test out: https://www.aircraftspruce.com/cache/400-400-/catalog/graphics/05-04457.jpg Aircraft Spruce is the source.

Increase the pressure. That's what I said in my post.

I'd like to increase the static pressure on the center of the bodywork/wheelbase. I don't need any aero drag reduction, as the car is fast enough down the straights (the car is light enough where I have a respectable power to weight ratio), but I'd like a bit more traction during cornering, and the extra drag of this mod would just help slow the car down at the end of the straights.

I'm looking for any mods that aren't terribly obvious to the casual observer.

 

[phantomjock]

Yeah - Ok I got it now...

I thinks the challenge; "... lies not in our stars, but in our "cars"..." Sorry Shakespeare

The car presents itself as an analog of a wing. So getting a high pressure over the top of the car would take some real doing. Consider the following comparison:


A vert may have more potential downforce over the center of the body - due to turbulent flow -- maybe not.

Hopefully the image shows how the shape acts like a wing and creates low pressure on the upper surface -- just like a wing.

The question might be changed from; "How do I create higher pressure on the top of the car", to; "How do I get lower pressure underneath?" It is really about the differential in pressure.

The underbody offers many "unseen" opportunities to create a low pressure area(s) and place it where you want - center of the body. You'll give up some ride height - maybe - but it would be unobtrusive and should be consistent throughout a speed range. That is to say - no pitching moments as you accelerate/slow down.

Your Pace Car style front spoiler should offer some help in the corners you mention. Additional drag through "Active Aero" would also play well for braking - but not all racing associations permit these.

Hope that info is useful.

Cheers - Jim

 

[rtj]

Make new rocker moldings out of thin aluminum which are 1 to 2 inches longer. This will act as side skirts keeping flow out from underneath. Lower is always better for side skirts.

Creative use of black paint could disguise how low they are.

Also, the spare tire area is a mess, a diffuser would be too obvious for your goal, at least a smooth under belly would help.

 

[69427]

Make new rocker moldings out of thin aluminum which are 1 to 2 inches longer. This will act as side skirts keeping flow out from underneath. Lower is always better for side skirts.

Creative use of black paint could disguise how low they are.

Also, the spare tire area is a mess, a diffuser would be too obvious for your goal, at least a smooth under belly would help.

We're on similar wavelengths here. Several years ago I pulled the stock rocker panels off and made 2" lower/wider replacements with Lexan sheet, and painted them semi-gloss black. I like the looks better, and so far no one has seemed to notice the change.

I had an aluminum bellypan on the car for a year or two, but my unscientific perception of the setup convinced me that the weight (about 30#) was hurting me more than any actual aero improvement was helping.

I've also looked into doing something at the rear, but so far I can't justify the weight of a diffuser. My current direction is to reduce the slight understeer I have, and ignore the rear until it becomes the limiting factor during cornering.

 

[69427]

Yeah - Ok I got it now...

I thinks the challenge; "... lies not in our stars, but in our "cars"..." Sorry Shakespeare

The car presents itself as an analog of a wing. So getting a high pressure over the top of the car would take some real doing. Consider the following comparison:


A vert may have more potential downforce over the center of the body - due to turbulent flow -- maybe not.

Hopefully the image shows how the shape acts like a wing and creates low pressure on the upper surface -- just like a wing.

The question might be changed from; "How do I create higher pressure on the top of the car", to; "How do I get lower pressure underneath?" It is really about the differential in pressure.

The underbody offers many "unseen" opportunities to create a low pressure area(s) and place it where you want - center of the body. You'll give up some ride height - maybe - but it would be unobtrusive and should be consistent throughout a speed range. That is to say - no pitching moments as you accelerate/slow down.

Your Pace Car style front spoiler should offer some help in the corners you mention. Additional drag through "Active Aero" would also play well for braking - but not all racing associations permit these.

Hope that info is useful.

Cheers - Jim

My reason for trying some aero mods at the cowl area is that it is the only spot on the upper bodywork that is shaped correctly to cause downforce/drag. Pretty much most all the rest of the forward section of a C3 is shaped to cause lift.

In addition to the PC spoiler, I've got a bellypan under it (the PC spoiler), extending back for a few feet, to reduce lift. I'm going to put a 2" air dam at the front of the spoiler to further reduce the air flow going under the car. I've also got most of the front grillwork blocked off to reduce the airflow into the engine compartment. I've also got some horizontal aluminum sheets at the bottom of the firewall area to block air trying to leave the engine compartment and going under the car. I'm trying to persuade the air to instead go out the side louvers.

 

[rtj]

Well, keeping it looking stock makes it tough.

Convertibles supposedly have lower drag coefficient. But, that won’t help.

Maybe try messing with how the t-tops fit. Could throw a couple of layers or duct tape across the front lip of the t-tops and see if that helps at high speed.

Lower is better for skirts and spoilers. There is vinyl wall molding (floor molding) that holds up pretty good and is cheap. Hardware stores sell it in rolls, pretty wide too.

 

[phantomjock]

I have been developing an interest in using surface roughness in lieu of vortex generators. It might make an interesting thesis for an up and coming student that had access to some "tunnel time." I found a study using both surface roughness and VGs on wind turbine blades. They found a decrease the lift coefficient by about 20% using surface roughness on the leading edge of the airfoil. You could sort of replicate that by using long strips of sandpaper attached with double stick tape to the hood. I think you'd want to first have some tuft studies to see if you are really tripping the airflow. The nice part you could move the "device" to get the result (if any) where you want it. Unfortunately, you'd be relying on the "Butt-Dyno" for comparative analysis. Naturally that wouldn't be really unobtrusive at first, but could maybe use some truck bed paint/liner to get the same effect.

This all goes back to a NASCAR legend when (Team Penske and Mark Donahue - as I recall in their Camaro) added a vinyl top to the car. They got a noticeable advantage, and later forced to remove it. There was some discussion at the time as to was it really an airflow device - or just hiding a lower weight roof section.

Skirts and some underbody shaping could also make useful improvements.


Cheers - Jim

 

[rtj]

This guy has a good point. Raking the body can add downforce. Greenwood’s tube chassis cars had a lot of rake.

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

 

[phantomjock]

Haven't looked at it (yet)- but will after this weekend. Currently on the road and at the track for a test day on the SR.

Raking the nose down (with a flat floor/underbelly) makes for a long diffuser. Also it effectively puts the entire car (consider the general shape like an airfoil) at a negative angle of attack. Then it will generate less lift too. Double good - eh?

Cheers - Jim

 

[rtj]

Nice discussion of new ground effects allowed in F1.

[ame]https://www.youtube.com/watch?v=hk-JKrs0rrc&app=desktop[/ame]

 

[rtj]

Pretty far out, so many small adjustments.

[ame]https://www.youtube.com/watch?v=kV-F40nWlUI&app=desktop[/ame]

 

[rtj]

Lots of negative comments on this one. Kind of neat, but why? That thing that pops up must increase cd.

[ame]https://www.youtube.com/watch?v=fSQxN6rJ1qg&app=desktop[/ame]

 

[phantomjock]

Been meaning to follow up here - great video and interesting approach. And, surprisingly - it does fit into INTERNAL BODY AERODYNAMICS as well! There are a few interesting points in the video -- like wear a helmet/goggles as bugs, rocks, etc. Don't follow the "path". and the speed range was intersting. For those not wanting to check the video try this on:


By the way - incase you missed it, I offering one of my Hoerner texts at a special VM price link here: http://www.vettemod.com/forum/showthread.php?t=11674
it is a great bargain at the price for its condition --NEAR PRISTINE--and worth its weight in gold for its information regarding fluid dynamic drag!

Cheers - Jim

 

[rtj]

You get a good look at the rear diffuser, also the front and rear fender flares are chopped off on the back up to the wheel center height.


[ame]https://www.youtube.com/watch?v=mCElwtx05pU[/ame]

 

[vette427sbc]

Reinforcing some aero stuff Pappy pointed out earlier on his Viper regarding wheel well exit ducts... I have a McLaren 720s In the shop with some cool wheel well aero.
Two huge ducts on each corner of the bumper feed coolers, and then exit out the side of the bumper AND the wheel well towards the side of the car.






And a nice contoured exit duct behind the front wheel:





This car should be here for a few more days if anyone has any pic requests... its an engineering marvel. Ill be looking over the rest of the aero... this was the first thing that caught my eye

 

[phantomjock]

AWESOME!!!
Real LIVE Spy pics!
WOW - I hope you are not sorry to have asked:

1. What is going on inside the engine bay?
2. How about the radiator and splitter/diverging ducts you've shown us-- inside the hood?
3. Rear fenders - are the ducts venting from wheel well - or intakes to the well?
4. Rear (bumper area) exits - are they "fully open" to the rear wheel wells - or shaped ducts?

This guy has some smarts - but I think he dresses himself: https://youtu.be/SlQEXQMQ75Q

Thanks in advance - hope you get to try it out!

Cheers - Jim

 

[rtj]

Reinforcing some aero stuff Pappy pointed out earlier on his Viper regarding wheel well exit ducts... I have a McLaren 720s In the shop with some cool wheel well aero.
Two huge ducts on each corner of the bumper feed coolers, and then exit out the side of the bumper AND the wheel well towards the side of the car.

Now I see, the air exits in front of the tire and is directed outwards. Kind of like the F1 in some respects where they create that vortex.

The largest opening is below the orange marker light, right? It kind of blends in.

 

[vette427sbc]

Now I see, the air exits in front of the tire and is directed outwards. Kind of like the F1 in some respects where they create that vortex.

The largest opening is below the orange marker light, right? It kind of blends in.

Yes thats correct...
I had a bit of a crazy week at the shop during that cars visit so I didnt get to do much more investigating... But I have a few other interesting ones here this week that I snapped some more pictures of.

Please excuse the poor picture quality... my iphone has seen better days :crap:

The F430 has very similar front ductwork to the mclaren. A bumper exit, and a wheel well exit, towards the outside. I also find it interesting that some portion of the wheel well vent on both the mclaren and ferrari direct air DOWN.



This is kind of odd though... the center duct has no purpose for coolers. But instead it necks down to almost 1/3 the size of the opening and goes under the car. Maybe an attempt to speed up airflow under the car? Or possibly a case of form>function


This is looking towards the front of the car showing the bumper duct to the belly pan


It also has a vent in the rear of the rear wheel well. The vents are directional based on front/rear of the wheel. This vents to a large opening in the rear bumper.



On the ford GT, there is NO wheel well venting, front or rear. The only heat exchanger is the radiator, and that vents from the hood. Vent opening in the bumper is 28"x5" (140in^2) and the exit is two 13"x9" openings (234in^2 combined)



The only other interesting aero on the GT is a small wicker on the rear, and a pretty functional looking rear diffusor (Ill grab pics of that later) Otherwise its pretty mundane (aero-wise!) This is a Heffner Twin turbo car. I bet its anything but mundane to drive!

 

[rtj]

Interesting on the downward jets at the front. VTOL jets in hover with forward motion might be analogous. Basically the downward jets impacting the ground roll up and force the on-coming air to divert around. Of course the speed ratio is way higher for hover. (Jet speed over forward speed). I’ll see if I can find a pic.

Congrats on getting such cool cars in your shop.

 

[BBShark]

Wow! You get a "hands on" look at the best of the best.

 

[rtj]

Took a bit to find the search term, but this works: jet ground plane in cross flow.