Flow Illustrator Tryout

[Arragonis]

Just for fun I tried the Fabia in the flow illustrator - not very neat pictures (I don't do drawing very well). One with rear spoiler

http://www.youtube.com/watch?v=OQv6MJ06fG4

Then I took the spoiler off

http://www.youtube.com/watch?v=7J4vxH9KiNQ

Then put on an unscientific kamm-back

http://www.youtube.com/watch?v=mayzFzXBg3A

I also did a 'basjoos'd version but it won't upload. Might have another play later.

[Piwoslaw]

It appears that the spoiler helps, but this could also be the roughness of the drawings.
That Kamm's angle should be a little steeper (12°), it looks flat-ish.

[Arragonis]

12 degrees downwards from the roofline ? I may try that later. Helga is staying so the Aero changes may start before winter comes.

[Piwoslaw]

Originally Posted by Arragonis

12 degrees downwards from the roofline ?

12 degrees from horizontal. And since the roof already has a 2°-3° slope, the roof-to-kammback transition will be gentler.

[cfg83]

Arragonis -

I agree with Piwoslaw, you want a downward angle that follows the "teardrop" shape. This is what I surmised would be best for my wagon :

http://www.youtube.com/watch?v=DxJR2CXrKnY

CarloSW2

[ChazInMT]

Couple of things I notice here.

1st, You need to make the vehicle much smaller to get any decent result. Flow illustrator will use the sides as physical perimeters and you won't get an aero picture of your car which is accurate...unless you want to know how your car performs in a 12 ft tunnel with a 60MPH wind blowing through it.

2nd, Dr. Chernyshenko is pretty specific that the RE be set between 100 and 1000 for cars. From the looks of these you have it in the 3000 + range. (Be sure to push the Submit button after changing the parameters)(Not that I've ever forgotten to do this)

Here is a beetle at Re=750 dt=.02, the dt tweak lets the flow settle quicker, so at the end of 10 seconds, you have a good idea of steady state conditions. Even this car is a bit too big for this application. I'd have been better off making it 2/3rds this size.

Also, when your "Model" is smaller and pushed to the left, you get to see the wake in back which is the real key to all this effort here.


Hope this helps!

New Beetle Re 750

[Arragonis]

Many thanks Chaz - I didn't know about a few of those things. I shall redo the images and resubmit.

[Arragonis]

Chaz - checked again and my RE was the default of 1000. In fact apart from movie length all my settings were the default ones. What total size was your image, I used the 256x125 one.

[Arragonis]

Right - starting point done again - does this look reasonable ?

http://www.youtube.com/watch?v=nncoYnz5uyw

If so I can fit a simulated Kamm-back again tomorrow.

EDIT - This one is higher than before as mine is not lowered like the Fabia I originally used as a model.

[cfg83]

Arragonis -

The "safe" bitmap size is 256x128. If I were you, I would make a 256x128 2-bit (black and white) bitmap. These are the rules I followed in my image :

(JPEG for browser visibility)

In terms of inputs, I use these :

Re = 2500000 (calculated for about 55mph)
dt = 0.01
length = 40sec
cutoff level = 40

Other than the time length, the inputs have been debated a lot, so I don't know if they are the right ones. IMO they do make the flow "more granular". Also, the 40 seconds allows the flow to stabilize.

CarloSW2