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Old 07-11-2008, 12:36 PM   #1 (permalink)
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Thumbs up Flow Illustrator - a simple windtunnel simulator

Howdy, all... just thought I would share this nifty FREE wind tunnel simulator that I sumbled across with y'all. This is not an ad, I am not affiliated with them in any way... it is just a cool tool for playing with aerodynamics.

Warning: it is VERY simple, 2-D and any results that it gives should be considered "rough estimates".

That being said, here is is:
Flow Illustrator
Flow Illustrator home page

Be sure to read the "Home" and "More Info" pages before diving in. There are some limitations to the movies that are not documented. It appears to die if you create a movie that is greater than 2mb. The best combination I have found is to use black-and-white BMP silhouettes that are 256x128 and the default settings with the exception of the time, which I cannot get to go longer than 25 seconds. YMMV.

Anywho, to see what I am talking about, here are some frame grabs I got from a simulation I did for my Ford Festiva, investigating different spoiler designs:

Stock Car:


Attached Spoiler:


Detached Spoiler:


Again, the program itself kicks out movies, and the above are just frame grabs from said movies. Note that for the simulations that I did, it took 10-15 seconds for the simulation to "settle down" and for stable patterns to appear. So keep your BMPs small to allow for maximum run times.

Everything I know about this program I got from their website, or I have noted above. Please don't ask me any hard questions, as I promise I won't know the answers!!

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Last edited by thirdman; 07-11-2008 at 12:45 PM..
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Old 07-11-2008, 12:45 PM   #2 (permalink)
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Also, my conclusions so far are that the following are good things that are easy to accomplish:
1) A small, flat, parallel to the ground, level with the roof spoiler.

2) Reduced airflow under the car, either through lowering or air dam & skirts.

No big surprise there, right? It is just really cool to SEE how this stuff can change air flow.

As always, YMMV.
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Old 07-11-2008, 01:07 PM   #3 (permalink)
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now if I just knew what Re and dt are supposed to represent...
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Old 07-11-2008, 01:16 PM   #4 (permalink)
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dt has something to do with the speed of the "wind". Very small changes make a big difference... going from .01 to .05 made it show standing shockwaves all along the hood, so I am guessing that was REALLY fast. I am doing some runs now with dt's in the .02 and .025 range to see if I can tell what is going on...
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Old 07-11-2008, 01:20 PM   #5 (permalink)
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That's way cool. I'm gonna toss in my '69 CST/10 for kicks
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Lets see how far it can go

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Old 07-11-2008, 01:48 PM   #6 (permalink)
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Doesn't seem to do as well with top-down views of my car as it does side views. Very nifty and can't beat the price
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Old 07-11-2008, 01:50 PM   #7 (permalink)
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Great find I've been lookin for something like this to better understand flow.
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Old 07-11-2008, 01:55 PM   #8 (permalink)
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Quote:
Originally Posted by i_am_socket View Post
now if I just knew what Re and dt are supposed to represent...
Reynolds Number = ( L * v ) / 'nu'

L = Effective length (or diameter of pipe) [m]
v = velocity [m/s]
'nu' = Greek letter 'n' = kinematic viscosity [m^2/s] (~1.6*10^-5 for air @ 20C)

Re is an indicator of effective flow when comparing scale models of real things (3/8 scale, or ?) - 2X speed for something half the size. So, in the modelling programs, a correct Re must be used.

For nearly all objects there is a typical Re number where transition occurs from laminar to turbulent flow. (a Moody diagram [pipe flow] shows this well)
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Old 07-11-2008, 02:11 PM   #9 (permalink)
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Quote:
Originally Posted by co_driver View Post
Reynolds Number = ( L * v ) / 'nu'

L = Effective length (or diameter of pipe) [m]
v = velocity [m/s]
'nu' = Greek letter 'n' = kinematic viscosity [m^2/s] (~1.6*10^-5 for air @ 20C)

Re is an indicator of effective flow when comparing scale models of real things (3/8 scale, or ?) - 2X speed for something half the size. So, in the modelling programs, a correct Re must be used.

For nearly all objects there is a typical Re number where transition occurs from laminar to turbulent flow. (a Moody diagram [pipe flow] shows this well)


So what are the best numbers?
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"All I know about music is that not many people ever really hear it. [...] But the man who creates the music is hearing something else, is dealing with the roar rising from the void and imposing order on it as it hits the air. What is evoked in him, then, is of another order, more terrible because it has no words, and triumphant, too, for the same reason. And his triumph, when he triumphs, is ours." -Sonny's Blues
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Old 07-11-2008, 02:25 PM   #10 (permalink)
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Awesome, Thanks!!!

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