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Alex W said:
A splitter is actually something I am working on (although not necessarily on a stock car / stock height).

Speed flaps are another I would like to try. Honestly, I just havn't been able to find / make the time to work on this lately. Spring / summer brings too much need to work on my actual car, rather than a computer model of my car :)
Would you mind uploading your model?
 

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Alex W said:
A splitter is actually something I am working on (although not necessarily on a stock car / stock height).

Speed flaps are another I would like to try. Honestly, I just havn't been able to find / make the time to work on this lately. Spring / summer brings too much need to work on my actual car, rather than a computer model of my car :)
Very interested in seeing what the splitter and speed flaps can do

David
 

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Alex W said:
<snip>
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.
<snip>
How cool is that? I recently picked up a SW20 for a track car, and have been reading the various posts in these forums to learn as much as I can. Then I find that a tread I contributed to in the Supra community is being referenced here.

I'm certainly interested in improving the cooling and reducing lift on my project car. I *love* that this forum has a set of subforums for engineers.
-Dan
 

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k guys,
I am running a hardtop MK2, V6 powered, 5 spoke 17" wheels, 235 40 17 on all 4 corners...
at Daytona in May.
I need the aero perfect with as little drag as we can get.
No side windows. the rear triangle windows installed.

can I have the image of the MK2, tops in, no spoiler.

I am talking with some NASCAR wind tunnel guys.

We ran the ModSquad 1 at Charlotte with an APR rear two element wing and a front splitter (not installed correctly) with lawn edging around the front of the splitter.
and the car handled awesome.



ya, the door is ____ed up. but the 62" wing worked awesome, and the nose stuck like glue.
 

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Did anybody recieve the model? :rolleyes: I want to decide what splitter and rear wing configuration can make some downforce difference, so will greatly appreciate if you can share with this model.
 

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Alex W idea to analyze aerodinamics of MR2 in Solidworks was really inspirational, so i decided to develop further and make my own tests.
It took me several days to sort with solidworks and converting model, but i think it worth it.

My force numbers don't match Alex ones in terms of absolute values, but i think more important is difference between different setups then values itself. I don't know what equation Alex used to calculate Drag coefficient and not sure how actualy car manufacturers calculate their coeffs, so i'll better write Drag force numbers instead. Units will be in metric system. Test was made at 100 km/h speed (~62 mph).
Also i have found that Alex made a mistake, probably with floor speed direction, because i don't have those velocity vectors that going up from the floor surface.
Added to simulation heat from radiator. Average radiator temp 76.6C = 170F.

Model:


 

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Engine bay cover. Drag force 236 N. Lift force 130 N.
I was sure that it doesn't improve drag force a lot, but i was surprised that it actually increase lift.

Velocity

Pressure

Temperature
 

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Not being a fluid dynamics expert, and knowing virtually nothing about the metric system. Mind putting some of those numbers into English?

Lift force is how much down force or up force the car has? Since there is only one number I am guessing it just averages out the front and rear? Anyway to see the down force for the front and rear separately?

There seems to be a lot of turbulence at the windshield/roofline. From the little I know that would see to be a lot of drag at that point? Is there anyway to lower the drag at that point? What would be causing it?

Another thing that stands out is the radiator inlet, would changing the shape of that or making it smaller significantly help the drag? I also wounder what the effect would be of venting the radiator through the hood would be, a factor that I doubt the software can take into account is the hotter air that would be coming up through the vents might play a little different on the areo of the rest of the car (at least that is what I have heard about cars like the Ford GT).

Venting it through the hood would also allow for a completely flat underbody, wounder what that would do.

Good work!

P.S. would you be willing to share the model so others can play with it? I would like a copy to play with myself even if I am not very good at solidworks yet.
 

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Texas Ace, i am not an expert too ;) This is only units, you can easily convert them with any converter in the internet, i hope that isn't a problem.
Lift force is how much air tryes to lift the car body up. So negative lift is downforce. Yes this are averages. Solidworks can calculate global forces and surface forces. Those forces i wrote same as in Alex W tests - global force minus surface force of floor. That way we can calculate actual force on hte car. Teoretically we can calculate surface forces acting on one half of a car, but because of a lot of polygons in the model, my computer can't calculate it (freezes or crashes). But i made test with only one detail change in each, so you can see how much force at rear gives the wing or how much at front gives the splitter.
There need to be more research to analize windscreen/roofline, as i said i am not an expert.
You have a great idea about heat going from radiator! I already made first test and it can be modeled and it affecting lift and drag a little ;) Of course i think we can't have a temperature difference across radiator, but some average temp would be good. What average temp do you think real radiator has?

I will make more testing, and of course try to model full diffuser and venting through the hood ;)
As for model. It actually isn't positioned as for free access, i made only some simplifications, remeshing and converted it (it wasn't easy though). So i will try to contact the author and ask him about such possibility.

Eric6, thanks. Yeah, diffuser is working, and bigger one is working even better :) I need to experiment with car ride height too.
 

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So since the lift force appears to be a positive number (unless you forgot the - sign), I am guessing that there is no downforce from an areo standpoint and it is staying on the ground purely due to the weight of the car? It would be nice to see the difference from the front and rear downforce to see where the light front end comes into play.

If it is areo based then a splitter and/or venting the radiator through the hood would seem to help the front end stay down a lot. If it is just lack of weight then that is another matter.

Bring us to the radiator venting, I am not too sure what the exiting temps would be from the radiator. The coolant temps going into it will generally be in the 180-200f degree range, it is not 100% efficient of course so figure the outgoing air temps in what, the 140-150f degree range? That is math a little outside my ability past an educated guess.

Look forward to seeing more testing, I got in this thread late and missed a lot of the first pages (need to go re-read them).
 

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100 N is approximately 10 kilograms of lift... 10 kilograms is like 22lbs.

100000 Pa is the same thing as 1 bar, or the same thing as 14.5psi... We call this 0 psig for normal atmospheric pressure, so when it says 101000 Pa, that basically means 0 psi. In this test the pressure differential is only a fraction of a psi.

90 kph is about 55 mph. So these tests were performed essentially at 55mph...

Hope this helps Ace...
 

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The way Outlaw wrote the results is a little weird. You either have down force or lift, you don't have both (as far as net reaction on the car). The friend I had do mine, he said at 100MPH it actually was creating LIFT, about 100lbs (at this point and onward, the car is being held down by the weight of itself and nothing else).

So for Outlaw's experiments, take down force and subtract lift, that is the net down force on the car.
 

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l0ch0w said:
100 N is approximately 10 kilograms of lift... 10 kilograms is like 22lbs.

100000 Pa is the same thing as 1 bar, or the same thing as 14.5psi... We call this 0 psig for normal atmospheric pressure, so when it says 101000 Pa, that basically means 0 psi. In this test the pressure differential is only a fraction of a psi.

90 kph is about 55 mph. So these tests were performed essentially at 55mph...

Hope this helps Ace...
That does help, was too busy to go look up any conversions online today. Thanks.

So from what you and eric said I am a bit confused at what the difference in between the "drag force" and "lift force".

The way I was reading it was the drag force was the air resistance to forward motion. Lift force was how much downforce (or upforce as it appears to be) the car had. Is that correct?

If it is really upforce on the car then that would explain why the front end gets so light since the front splitter made a bigger difference then the rear spoiler.

Really makes me wounder what venting the radiator through the hood would do, it has always bothered me having it vented through the bottom from an areo standpoint, the shape is basically a reverse splitter pushing you up IMHO.
 

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l0ch0w said:
90 kph is about 55 mph. So these tests were performed essentially at 55mph...
Actually test was made at 100 km/h ~62 mph as i wrote in my first post. It just the air start to slow not very close to the vehicle. If you look at left top corner you will see yellow color is darker.

The way Outlaw wrote the results is a little weird. You either have down force or lift, you don't have both (as far as net reaction on the car).
Hmmm... Why my number weird? Yes the car experiencing lift. For example as i wrote stock car at 100km/h has Lift force = 100N. That men it has downforce = -100N. Whats wrong with that? If car will be experiencing downforce after some changes then my numbers of lift force will be negative.

The way I was reading it was the drag force was the air resistance to forward motion. Lift force was how much downforce (or upforce as it appears to be) the car had. Is that correct? If it is really upforce on the car then that would explain why the front end gets so light since the front splitter made a bigger difference then the rear spoiler.
Yes, that is correct. Lift force = "upforce" = negative downforce. I can write numbers as Downforce if it is easier to understand :)

The coolant temps going into it will generally be in the 180-200f degree range, it is not 100% efficient of course so figure the outgoing air temps in what, the 140-150f degree range? That is math a little outside my ability past an educated guess.
Yeah, i think it will be in this range too. Then i will recalculate all results with 170F average radiator temp and then will proceed to further tests.
 
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