Did a CFD Analysis on the MKI - Interesting - MR2 Owners Club Message Board
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post #1 of 178 (permalink) Old June 4th, 2007, 23:00 Thread Starter
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Did a CFD Analysis on the MKI - Interesting

Ok, I just got around to playing with the MKI in FloWorks at work. Granted it's a profile 2d analysis on my 5min eyeball sketch from a picture, it was really useful to see what certain things did. Everyone wonders about the air above the engine lid. That rapid drop off from the rear window makes the air go in a giant circle above the engine/trunk area. With the front of the car pointing left, the air goes in a clockwise circle. Half of the air that comes from underneath the back of the car joins this parade. This intersection is about where the stock spoiler is. Needless to say the stock spoiler doesn't do anything for downforce, as it's located smack dab in the middle of tumbing air. I also learned that a wing doesn't work until it's at least above the roofline. Any lower and the air underneath the wing is not streamlined and doesn't create a low pressure zone, which is what makes the wing work. I also learned that the front airdam works primarily by creating a low pressure zone under the front of the car, however, my 5min model was a solid profile, so this is probably only true if the underside of the car is completely sealed.

I'll do some more accurate models in the next couple days and post some pics of the pressure and flow fields. I'll try including empty space for the engine bay to see which way the air goes. This is really fun! I just bought a rear wing and it looks like I'm going to have to mount it on 2"x8" hollow aluminum rectangles to get it high enough to function.
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post #2 of 178 (permalink) Old June 4th, 2007, 23:40
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great now do a mk2!!!! I cant wait to see the results!!!!
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post #3 of 178 (permalink) Old June 5th, 2007, 00:56
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No diagrams?

We had someone do something very similar a couple years ago. A 2d analysis should be taken with a grain of salt... it can only be so accurate. But I'm still waiting on a real in-depth 3D analysis. I have a model made (spent a heck of a lot of time on it last summer), but I have been very unsuccessful with FloWorks this far. If you have any more expertise I'd be happy to send you the model I have, this is the specific reason I spent so much time on it.
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post #4 of 178 (permalink) Old June 5th, 2007, 01:10 Thread Starter
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Please send it to me! [email protected]com I'll do FlowWorks on it.
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post #5 of 178 (permalink) Old June 5th, 2007, 09:11
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please send it to me also, i am now at the point of designing downforce for my car
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post #6 of 178 (permalink) Old June 5th, 2007, 10:47
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please forward all infoto me as well as I really need this for the V8 Mr2~
Can you show what the air flow is doing at 150 mph, 175 mph and 200 mph on the MK1?

Also can I see a screen shot of the flow with a wing above the roof line? How far did you place it?
How about moving a NACA profile wing further back, say with the trailing edge even with the rear bumper?

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post #7 of 178 (permalink) Old June 5th, 2007, 11:26
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Is floworks included with Solidworks? looking at the student price now...

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post #8 of 178 (permalink) Old June 5th, 2007, 13:47
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floworks is an add-on, its part of the COSMOS works package
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post #9 of 178 (permalink) Old June 5th, 2007, 20:55 Thread Starter
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Ok, I literally only had 10min. to work on this before they kicked me out of the office. I had to make modifications to bentheswift's model. It wasn't made to scale, and the profile was off, esp. at the roof (don't mean to bash, I really appreciate it). This was done at 100mph. You can see how useless the factory spoiler is. You can also see how high a rear wing has to be in order for it to work at all. Tomorrow I'll try to make some better revisions to the model and play around with some aero tricks.

You can't really see the details of the arrows in the back, but they're going in a circle. Is there a free image host out there that won't resize my pictures?
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post #10 of 178 (permalink) Old June 5th, 2007, 20:58 Thread Starter
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Ok, I figured out how to retain the image size in photobucket.
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post #11 of 178 (permalink) Old June 6th, 2007, 17:40
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Well now, finally some results!!!

I think I sent you an older version of that model, but it shouldn't affect it really.

The simulation is not quite accurate yet, but this is a big step. Maybe I will spend some time after finals and rebuild that model to scale.

SP, is there any way I could get you to help get me started with FloWorks? I've tried messing with it in the past and have never gotten squat out of it.
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post #12 of 178 (permalink) Old June 6th, 2007, 23:05
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add air flow to the engine bay and that will change significantly.
is this based on a 3d car? or just two dimensional? Like is it taking into account the rear window area between the flying buttress?

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post #13 of 178 (permalink) Old June 6th, 2007, 23:15
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Ya that's a 3d car. I'm not sure whether the simulation ran it two-dimensionally or if it is just a profile view. I am pretty sure that FloWorks can do 3D CFD, even though I've never actually seen a sim.
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post #14 of 178 (permalink) Old June 6th, 2007, 23:21
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I overlaid an image I found of the web. it is slightly off and I cut it out quick. but yes you can see the scale is off a bit
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post #15 of 178 (permalink) Old June 6th, 2007, 23:53 Thread Starter
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Ok, I completely redid the 3d model to make it more accurate. That was a pain.
I added an empty space for the engine bay, and I also created vents in the
engine lid. The first picture shows the surface pressure on the car, along with
superimposed velocity vectors. The closer spaced the vectors, the more the
velocity is changing, the longer the vector, the greater the velocity. Nothing
too exciting here - I'm just showing you that 3d analysis is possible.

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post #16 of 178 (permalink) Old June 6th, 2007, 23:56 Thread Starter
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This picture shows a section view with pressure indicated by color and velocity
again indicated by vectors. Points of interest are the terrible airflow over the
stock spoiler, and the minimal airflow through the engine bay.

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post #17 of 178 (permalink) Old June 7th, 2007, 00:01 Thread Starter
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Here is the interesting one, both color and vectors indicate velocity. In order to
study the dynamics through the engine bay, I changed the scale to 0-10mph.
Fully red means 10mph and above. You can see that the air through the engine
bay is around 2-3 mph. Remember this is modeled with the car going 100mph.
The more effective your front airdam, the less air that goes underneath your
car, the less air that travels up your engine bay. The engine bay is modeled as
an empty space, so in reality the flow is probably worse.

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post #18 of 178 (permalink) Old June 7th, 2007, 00:31 Thread Starter
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Ok, now I've modeled it with a 1250cfm fan blowing down from the engine lid. This is still
a cut-plot, but it's located where the fan would be. I've angled the view a little to give
it some perspective

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post #19 of 178 (permalink) Old June 7th, 2007, 00:35 Thread Starter
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Here is a double cut plot. One cuts through where the previous picture did, and
another perpendicular to it, at the engine bay. You'll notice in this model, the fan
pushes air down and some of it comes up through the vents. This is not completely
accurate for lack of an actual engine there, but goes to show that placing a fan there
to blow downwards is likely ideal. We've seen that natural velocity through the engine
bay is very small, so fan placement should have air temp. as the highest priority.

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post #20 of 178 (permalink) Old June 7th, 2007, 00:37 Thread Starter
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Here's a 2D cutplot located across the fan. Color is back to pressure. Notice that
with a fan sucking in some of the turbulent air, from that area, a high pressure zone
has developed on top of the factory spoiler. With two fans blowing down, the factory
spoiler may actually become useful. With fans blowing up, there is no hope for any
wing/spoiler.

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