Let's Talk Aero

[racer47]

Hoping. I'm going to figure out how to test that (wife's meat thermometer). Surely it will reduce lift and drag (good). If temp goes down, then we got all three.

Many low cost multimeters come with thermocouples. I think that would be much easier and more repeatable than trying to use any regular thermometer.

The truth is, nobody is 'very smart' on this stuff. None of it is truly intuitive.

Going back to page 3, to the quote above. AJ Foyt once said about aero at Indy "if I taped a beer can to my wing and ran a fast lap, next session everyone would have beer can taped to their wing" I remember that line because thats what we were doing at the time, just copying aero from fast cars.

 

[Fabman]

Many low cost multimeters come with thermocouples. I think that would be much easier and more repeatable than trying to use any regular thermometer.



Going back to page 3, to the quote above. AJ Foyt once said about aero at Indy "if I taped a beer can to my wing and ran a fast lap, next session everyone would have beer can taped to their wing" I remember that line because thats what we were doing at the time, just copying aero from fast cars.

Monkey see monkey do is still alive and some of them have racecars.

 

[Grant 302]

Going back to page 3, to the quote above. AJ Foyt once said about aero at Indy "if I taped a beer can to my wing and ran a fast lap, next session everyone would have beer can taped to their wing" I remember that line because thats what we were doing at the time, just copying aero from fast cars.

That's still happening. IIRC, back around '08 there was an F1 car that had an extra pair of horn shaped winglets on either side of the intake duct...started showing up on the competition shortly after.

 

[Grant 302]

Monkey see monkey do is still alive and some of them have racecars.

Whadya call me?

 

[Big Black]

More pics please...

Yes, maybe I'm going a little overboard. BUT, my hood is rock-steady at speed with the bulb seal, and it fluttered moderately without it, so $20 well spent, I believe. Not sure at all whether or not it has any positive effect on drag.

 

[Fabman]

Whadya call me?

Not you.

 

[Grant 302]

You know, I was kidding...

And good work BB. I've been meaning to do the same for a while.

 

[RES_22]

Whadya call me?

Cheetah?

Ouch....too easy.

 

[ChrisM]

Speaking of monkey see, monkey do, I may give that weather stripping thing a shot. Forcing air out through the top vents instead of the sides of the hood would probably increase downforce just a little bit and reduce hood shake since it's not jetting out the sides. Although if you're not venting enough air it would go out under the car, which is why we put big holes in the hood to begin with. I'd have to leave a little opening for my intake though.

 

[steveespo]

"My entry fee covers the whole track....Not just the part that you want me on".
-Sal Molinare

Quote of the year!!!!

 

[racer47]

Speaking of monkey see, monkey do, I may give that weather stripping thing a shot. Forcing air out through the top vents instead of the sides of the hood would probably increase downforce just a little bit and reduce hood shake since it's not jetting out the sides. Although if you're not venting enough air it would go out under the car, which is why we put big holes in the hood to begin with. I'd have to leave a little opening for my intake though.

I would just tape the hood shut first and see if it did anything before going thru the effort of weather strip

 

[Grant 302]

I don't really see a big difference in effort.

 

[Grant 302]

Water droplets help see streamlines and flow patterns. These are from yesterday @ ~80pmh.

Streamlines from vortex generators:


Attached flow across top of LS spoiler:


Streamlines on top of quarter panel:
Interesting that there's a stream that comes *up* the quarter panel to join the one already at the top:



From testing a while back:
Old VG (4) streamlines:



'New' VG (6) streamlines:



Normally, flow does not remain attached on the rear window/decklid except for the outer ~10" -12"
This is a stock '05-'09 S197:


Separates about halfway down rear window:
From Ford video:

 

[ChrisM]

What are you looking for with the water droplet tests? What do you want to happen?

 

[Grant 302]

So far, I used them to test various arrangements of vortex generators, base and LS spoilers, stock rake vs. level. Also generally to see/understand the flow patterns around both cars. It's also easier than doing yarn tufts and video.

I'd use oil if not for the clean-up needed. The hard part about using water is that it's better in cool/humid conditions and more subject to lateral G's when the droplets get too big. Small droplets don't move with low flow.

 

[ChrisM]

Do you want the water to show that air is staying attached or detaching at specific points? I can see differences in the pattern, I'm just not sure if what makes one better than the other.

 

[Grant 302]

Mostly, I am looking for changes toward more attached flow. At the back window I am looking to fill the separation bubble, and kill the lift from from it that would be perpendicular/'normal' to the surface of the window. The lift from the downward attached flow is a much smaller vector, and this flow contributes to more downforce from the spoiler across it's full width and the angle change at the base of the rear window, instead of just the outer sides.

 

[302BOB]

You guys are getting too scientific for me..good luck on your experiments...........

 

[Grant 302]

You guys are getting too scientific for me..good luck on your experiments...........

Nah. To engineer is human. And thanks, I could use a little luck keeping testing equipment taped on during testing

Do you want the water to show that air is staying attached or detaching at specific points? I can see differences in the pattern, I'm just not sure if what makes one better than the other.

Conceptually, this is what I'm after/observed:


Stock in red, flow separates and barely kicks up. For simplicity, the recirculating/stagnant areas not shown. I don't have pictures of it from the stock Boss or GT, but flow would separate about mid window on both cars. Low pressure on back of window and decklid are both summarized as drag and lift components. The base spoiler helps make this a recirculation zone, at least in theory.

Vortex generators added in green, pulls flow down energizing downward stream before it separates. Attached flow observed to base of rear window and on decklid. In theory, this action comes at a small drag (at the VGs) and lift penalty (from downward directed flow), but should net less lift and drag compared to stock. Then make the spoiler more effective for more downforce than just recirculation.

Laguna Seca Wing added in blue, benefits from redirected flow. Without the VGs, the wing mainly uses two large vortices that 'spill' over the sail panels (qtr. window area) that work with the wing on the outer sides of the wing supports. With the VGs, flow can be clearly seen as attached on the full width of the upper surface. So far I've measured dynamic pressures that 'match' car speed at centerline about 1/3 wing chord. I plan on testing more points, etc. as flow can be variable in the downstream vortices.

I found this CFD model on the internet recently:

Helped me feel a bit more confident that I'm changing things in the right direction. Wish I could find the origin of the model.

 

[Albino500]

A lot of aero talk for a box car......I like it.