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trebuchet03 03-31-2008 11:49 PM

Rolling Wind Tunnel CFD
 
1 Attachment(s)
I'm happy :D

I just figured out how to model a rolling wind tunnel for CFD analysis.... This makes me happy because ground effect plays a big role in drag :thumbup:

http://forum.ecomodder.com/attachmen...1&d=1207021467


To make sure it was working, I made the rolling ground move in the opposite direction at 250m/s - it created some massive crazy swirls :D

That was a super duper low resolution run - tonight I'll run a high resolution version to do some calculations with :D

OfficeLinebacker 04-01-2008 10:14 PM

OpenFOAM?

diesel_john 04-01-2008 10:58 PM

1 Attachment(s)
OfficeLinebacker , welcome to the site.



trebuchet03,
It is an airfoil big enough to enclose a rabbitt.

the excel plot is for a pickup truck
diesel

trebuchet03 04-01-2008 11:36 PM

Quote:

Originally Posted by diesel_john (Post 17442)
trebuchet03,
i know you don't have time, but how difficult do you think it would be to model a shape of this kind? diesel

What type of info are you looking for? That is, post a sketch on how you want it setup (do you want a ground, how far off?, velocity, size, etc.) and list what outputs you want.... I might not be able to do it immediatly, but if I can find the equation that governs that foil shape, I can model this in a few minutes and run CFD ;)

Quick search from google got a cool flow visualization...
http://legacy.ensight.com/news/airfo...animation.html

What's nice about NACA foils is that there's a lot of data on them already :)


And Linebacker, not FOAM - COSMOS FloWorks ;)

Cd 04-01-2008 11:46 PM

trebuchet03 : I was working on a 3D model of your Jetta. ( We discussed it on the Gassavers forum )
I just had to replace my hard drive, so my liscenses got messed up on the 3D program.
I, as well as a couple of others here and on the Gassavers forum would really love to see some tests done with the Jetta.
Do you think you will ever find time to run any tests ?

It would be nice to see what kind of figures could be produced by lowering the car and adding a trunk extention, since the Jettas' profile is almost identical to the Ford Fusion Bonneville car ( which if you recall scored a .21 .Cd ! )

trebuchet03 04-02-2008 12:01 AM

.cD

trying to parametrically model a car - from scratch - is incredibly hard (beyond the amount of time I'm willing to invest at the moment). Simplification won't yield much, if any, useful data considering the chaotic nature of this sort of system (small input changes yield great output changes).

But, I'm trying to come up with a way to reverse engineer large objects cheaply... I need to do more research, but right now the only solution I've got is building a large rotating platform and casting a laser line over the car and video recording it... Not practical at the moment as that platform would have to be motorized to move at a constant angular velocity (and cars are heavy :p).

If I can find or come up with a way to reverse engineer large bodies on the cheap - this wouldn't be limited to a Jetta :p

For reference... here's an expensive method
http://www.sammertech.com/measuremen...ry_session.jpg
Photogrammetry
you get....
http://www.sammertech.com/measuremen...ygon_model.jpg

in a .stl file -- techniques like this is how a full scale clay model is digitized for further analysis :D


EDIT:

As far as time is concerned.... Time to run tests is no problem... It's mostly a set it and forget it sort of thing. Well, maybe an hour or so of setup... It's just getting the model :p Doing things like that NACA are no problem if I can get that foil shape parametrically... Something like a car, freaking hard :D I'll have much more time this summer though :D

Daox 04-02-2008 09:14 AM

I might have to send a model your way for testing... :)

trebuchet03 04-02-2008 11:11 AM

.cD - look what I just found... Not a Jetta, but it's European cousin :D

http://www.3dcadbrowser.com/preview.aspx?ModelCode=8547

http://all3models.brinkster.net/th/1/8/8547.png

http://all3models.brinkster.net/th/2/8/8547.png

Too bad it's not a free download (but they have a stereo lithography format I can work with :D).... You get 1 download for every upload, I'm going to see what they're looking for in an upload :D

diesel_john 04-02-2008 10:21 PM

trebuchet03 -

that flow visualization is awesome.

i got the foil data from this site.

http://www.pagendarm.de/trapp/progra...les/NACA4.html

looking for the Cd for the shape in post #3 with the top and bottom splitters.

approx. 4 inches off the ground

cfg83 04-03-2008 01:29 AM

trebuchet03 -

Quote:

Originally Posted by trebuchet03 (Post 17508)
.cD - look what I just found... Not a Jetta, but it's European cousin :D

http://www.3dcadbrowser.com/preview.aspx?ModelCode=8547

...

Too bad it's not a free download (but they have a stereo lithography format I can work with :D).... You get 1 download for every upload, I'm going to see what they're looking for in an upload :D

You should do the following :

1 - Get 4 ecomodders to chip in $20 for the 5 download registration ($79)
2 - Download your car "for free" and one car for each ecomodder that pitched in.
3 - Model their cars using your software, any way they want ... UNTIL THE END OF TIME!!!!!!!!!!!!!!!!

Hmmmm, maybe it's not worth it for you.

EDIT: Here's the one I want (modded into a wagon, of course) :D :
http://64.78.14.108/ts/1/2/2224.png

CarloSW2


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