Did a CFD Analysis on the MKI - Interesting - Page 4 - MR2 Owners Club Message Board
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post #61 of 178 (permalink) Old June 12th, 2007, 18:01
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A couple things I'd like to point out about the drawings here. Especially since I have a copy of SolidWorks with the CFD package sitting next to me here waiting to be installed. (Won it at a state student technical drafting competition)

The front bumper I can see being a major major area of concern. However you really need to take into account the fact that it's not just a solid surface. A flatter bumper will be actually more aerodynamic from the stand point of looking at the entire car however with the angled bumper on the later generations it may be there to improve flow into the radiator. If this is the case having a Papal. style vent there would be even more effective than using a earlier gen bumper.

Just looked at the newest model and saw that it was made to be fairly open and made a really nice low pressure zone at the front. This might be further magnified with a Papel vent on the hood which would mean great things for creating a nice low pressure zone under the car.

I agree with Bill that the rear bumper needs some attention given to it as well. Having it a bit more accurate I think may change things quite a bit, along with how far that back section behind the rear wheels comes down.

A thought on that sunshade for the rear. I would like to think that it would clean up the air flow over the rear engine cover quite a bit. However I think this would put most of the airflow above the top of the spoiler and make it a bit useless unless you raised it up and back some. Check out flyin miatas "Track Dog" and the two different spoilers they use.

As far as improving all of this I think having a nice vent at the front of the hood would do wonders for the flow under the body of the car. Second I would say try both the first and second gen noses with this vent and having air travel through the radiator. You may find one will produce a greater low pressure zone at the front wheels while the other flows more through the radiator. Which would equate to a lower drag coefficent I'm not sure.

Perhaps reversing the flow of the fan on the engine lid to blow out would pull some of that air by the rear axels out and help speed up the air a bit more, would be ideal for the spoiler plus the addition of a simple rear diffuser could help this as well. If you did this have it pull some air from under the car for the engine bay along with the side vents then have it possibly vent out towards the license plate? I know the MR-S has a nice open vent right there.

As always, take this with just a grain of salt. I'm just a youngin who's throwing some ideas around. Anyone want to send me that model I'd appreciate it. User.is "@" gmail.com
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post #62 of 178 (permalink) Old June 13th, 2007, 00:37 Thread Starter
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Wow this thread is really becoming more involved than I'd anticipated! I really wish I had started with a more accurate model, but I initially just wanted to see how tall a rear wing had to be to get decent airflow across it. It turns out that the wing really has to be taller than the roofline for it to work how it's supposed to. The near vertical angle of the rear window causes any flow below roofline to swirl in large scale eddies. I think this is pretty definitive even with the inaccuracies in the model.

The second thing I really wanted to find out was how fast the natural flow through the engine bay was. The low pressure area behind the rear window draws air up, but any decent front aero work also reduces flow and pressure underneath the car. Regardless, the pressure differential is very small and only moves through the engine bay in single digit mph speeds (at 100mph). From this we can gather a few good design hints such as cold air intake placement (should be very low), and engine fans (don't need to focus too much on going "with the direction").

Airflow through the engine lid is somewhat of a compromise, because you can have a pair of fans blowing down from the engine lid, to help bring the swirling air down, to improve flow across the rear wing, but doing so also increases air below the trunk, which is bad. The opposite improves air under the trunk, but ruins air across the wing...

From here, I think we can refine the model to look more closely at finer details, and also play with certain aero devices.
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post #63 of 178 (permalink) Old June 13th, 2007, 15:27
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this is the coolest thread in a while. I'd really love to see an MK2 done.
superpilun please pretty please.
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post #64 of 178 (permalink) Old June 13th, 2007, 16:13
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I've done a very quick wind tunnel like simulation, and the overall airflow over the top, engine bay, and back of the model looks similar to superpilun's simulations done in flow works. So with a bit more work I think I can get some pretty accurate results.

I'll post up a you tube link to the animation later tonight if it's cool with you, I don't want to hijack a thread.

EDIT: I'm going to have wait a bit longer on that..

problem is since I'm using a smoke simulator, it's getting into the inside of the model through the body panel gaps and wasting a ton of processing power simulating the particles blowing into the mesh instead of over it. Not to hard to fix, just a little time consuming

It probably wont be able determine areas of high/low pressure like floworks can, but it gives a pretty decent idea of the airflow, and I think it could be useful for comparing different aero parts, like going wingless, stock wing, and plumley style wings.

..and if all else fails it will be at least be a cool looking animation
Just a few screen grabs from a real quick test:


Last edited by backspace; June 13th, 2007 at 19:58.
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post #65 of 178 (permalink) Old June 14th, 2007, 02:05 Thread Starter
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Dude, that's awesome man! What program are you using for this? Doesn't look familiar to me. This thread is all about getting the information out there, so by all means, please feel free to add whatever you have!
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post #66 of 178 (permalink) Old June 14th, 2007, 14:48
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FumeFX plugin for 3ds max. If you can figure it out- AWESOME program. It's really trial and error since there isn't much of a useful help file or too many tutorials out there, but I think I'm starting to get the hang of it.

It's simulated just like the smoke tests are in a wind tunnel. Their's a wind force blowing blowing air over the area, and then the smoke emitter placed in front of the car. It's really just a lot of tweaking settings to get it to work nicely, and it all depends on how well the model is setup for it. I haven't really gotten much of a chance to play with it yet.

Another route I tried is a program called RealFlow. Primarily a fluid simulator, but it can simulate gases.
I got some cool results, but because of the way it simulates, the results were nowhere near accurate.
It's seems the program is blowing air into nothing but empty space. It's nearly impossible to set up an "atmosphere" so that the air flows into the low pressure areas. Awesome program, just not really made to do airflow sims.
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post #67 of 178 (permalink) Old June 15th, 2007, 17:38
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Watching thread intently.........
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post #68 of 178 (permalink) Old June 15th, 2007, 22:27
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post #69 of 178 (permalink) Old June 16th, 2007, 10:03
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how does one go about making a 'model' of a car to be used in these programs?

yes i still have a handful of aw11's.
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post #70 of 178 (permalink) Old June 16th, 2007, 11:23
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Quote:
Originally Posted by feral4mr2
how does one go about making a 'model' of a car to be used in these programs?
This is a basic tutorial that's pretty generic for most 3d modeling programs.
http://www.evermotion.org/tutorials/..._modeling_max/

I've never used solid works, but I've heard it's similar to inventor, and modeling a car in a program like that is much more difficult and time consuming.
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post #71 of 178 (permalink) Old June 16th, 2007, 22:02
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I've never used inventor, I've only used Catia and Solidworks, but SW is a cinch to use. It took me a long time to build the AW11 model (probably 50 hours), but I did put a relatively large amount of detail into it and also learned a lot doing it. Building a more curved model like an SW is going to be a bit harder.

If you want to start modeling, the first step would be buying a copy of the program, which if you're not a student is going to be extremely expensive.

Backspace, a gas is a fluid. Liquids and gases are both fluids and they're modeled more or less identically as long as the velocity is below about 30% of mach speed. Maybe the reason that the simulation is not giving accurate results is because the density and viscosity of the air are off... (they appear to be unless the units are funky, but it doesn't show units)
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post #72 of 178 (permalink) Old June 17th, 2007, 13:19
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Just come over from TB. I had a chat with one of my friend's at work, into his CFD and he's interested in this thread. A couple of thoughts already, I don't think the flow vectors at the back necessarily tell the whole story, your exhaust is in a pretty good position, the low pressure at the back of the car is causing the recirculation. The exhaust is best placed exiting into lower pressure than higher pressure, you certainly wouldn't want it at the front facing forwards. Also, if any of the codes can integrate the pressure to get forces and moments - if you're trying to reach 200mph you want to make the car stable at the same time.

I'll try and keep involved, I am commuting a massive distance to work for the next month or so until i move house.
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post #73 of 178 (permalink) Old June 17th, 2007, 18:07
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Quote:
Originally Posted by bentheswift
Backspace, a gas is a fluid. Liquids and gases are both fluids and they're modeled more or less identically as long as the velocity is below about 30% of mach speed. Maybe the reason that the simulation is not giving accurate results is because the density and viscosity of the air are off... (they appear to be unless the units are funky, but it doesn't show units)
Shows how much I know!
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post #74 of 178 (permalink) Old July 5th, 2007, 09:26
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This is VERY cool. It also proves several things:

1) SC guys should really pay attention to this since it directly relates to airflow over the intercooler

2) Now I REALLY want to build my 1969 Charger Daytona type rear wing!

I'd like to see what would happen to that model if you placed a cover over the engine lid that went from the roof and just came down straight following the lines of the rear pillars. Id also like to see if it would make a difference for that same piece to be curved somewhat - where the bottom center would reach to the lip of the engine cover area. That way the rear area would be much "smoother" - at least that's what I'm thinking.

Bill, what is this "Papal" hood mod? Is it just an opening above the radiator area to vent pressure, as opposed to the frunk invasive style sccop? STRIKE THAT - I did a search and actually found the answer for a change!

Marc - Sold my MR2, now a Corvette driver :)

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post #75 of 178 (permalink) Old July 6th, 2007, 01:37 Thread Starter
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Ok, some empirical evidence. I put a turbo on my silvertop, and ran an air-to-air intercooler in the engine bay on the driver's side. I had one fan on top of the engine lid blowing cold air down through the vents (rain shields cut out). I also had a fan on the bottom of the intercooler sucking air down. I ran a track day in 100+ deg. weather and the intake temps were not stable, they rose quickly. This happened for two reasons: my intercooler was too small, and the fans didn't move enough air through it. The problem is, even with huge fans, you're not going to get air to move at 100mph through the intercooler like it would if it were in front of the car. Having given this some thought, a very good way to stay with air-to-air, without going all the way to the front, is to run the intercooler behind the roofline of the car, with its face along the same line as the roofline. Then attach a scoop to the face of the intercooler to create a high pressure area on top of the intercooler, and the low pressure area underneath will force tons of air through it. This is of course in the context of track events where you're on the throttle for long periods of time. The alternative is water-to-air with a front mount heat exchanger.
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post #76 of 178 (permalink) Old October 14th, 2007, 21:33
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This is the best post i have ever seen!
Fantastic.
Could we see a model with the air being pushed out the engine bay with a fan from underneath instead of the model pulling air down.
Getting the best possible air flow through the intercooler is my biggest interest in this post.
Also how about a diagram with the wing removed altogether? Do you think that would effect flow though the engine bay?
Cant wait to see where this post goes!
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post #77 of 178 (permalink) Old October 15th, 2007, 02:57
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Old but useful pics

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post #78 of 178 (permalink) Old October 15th, 2007, 03:03
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Quote:
Originally Posted by superpilun
Having given this some thought, a very good way to stay with air-to-air, without going all the way to the front, is to run the intercooler behind the roofline of the car, with its face along the same line as the roofline. Then attach a scoop to the face of the intercooler to create a high pressure area on top of the intercooler, and the low pressure area underneath will force tons of air through it.
Perhaps something like this:



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post #79 of 178 (permalink) Old October 17th, 2007, 09:22
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Wow excellent thread here guys!

Would be interesting (and technically valuable I believe!) to see what effect a Papal style vent has on the Aerodynamics of the mk1.

Also I'd be interested to see what effect a solid (vented perhaps) panel over the flying buttresses would have (like FeralAW11's mk1 in Australia).

I'm studying Engineering at Uni in Scotland and am rather excited about the work being done by you guys here!

Keeping a close eye on this thread
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post #80 of 178 (permalink) Old October 17th, 2007, 11:10
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so are we! I am willing to bet we will get more done over the christmas holiday season.

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