Extremely low drag values,...

[sabaman]

Hello.

I put a car in flow design and at 275% i get a drag value of 0.00, i highly doubt im an aero genius so theres obviously something (im doing) wrong, at 50% its 0.05, other cars do work fine though with the same settings (which is 3d, whatever percentage and 67m/s)

Any reason this can occur?...

[Jon.Wilde]

Hi Sabaman,

Just to be clear, this is the Simulation Resolution value that you are changing? 

Thanks,

Jon

[sabaman]

Yes the percentage yes, the funny thing is, this is a car i did in 2007 just wanted to see what it would do, now the higher percentage i go in the res, the worse it gets, i even got negative drag at 400%

If really necessery i can send you the model as a 3ds.

Sabino,...

[Royce_adsk]

I think it would be valuable if we could work with the model that you are using.  Could you private message me a download like through dropbox or something else similar?

Thanks,

[Royce_adsk]

Just letting you know I am looking at the model.  Can you post a screen shot of the results that you are getting?  So far my drag force is ~500N and drag coefficient is 0.11.  Very early in the simulation so those values are still dropping.

Thanks,

[sabaman]

What res did you put?

and 0.11 is allready way too low, if you go up on res, the more you go up the lower it goes,

Thing is, if i can recall correctly, i have a similar car, was a redesign of this actually though modeled not in rhino but a diff prog. and i had the same problem, dont know how, its only these 2 cars if im correct that had this.

I started my simulation now so when i have something ill post it.

Sabino,...

[hartogj]

Thanks for sharing this Sabino. I believe Royce and I are seeing similar, and there is something in the geometry file that is making this one unusual.

If I surface wrap the geometry and export an STL I am seeing more reasonable values close to 0.30. We'll send you a copy of the surface wrap file so you have it and have our folks look into the original 3DS in more detail.

Jon

[Royce_adsk]

Hi Sabino,

As Jon said, it has something to do with the geometry.

Initially, I was running with default mesh and I did notice the same thing you had where more mesh resulted in really poor results. 

Jon is going to share this with development to explore, let us know what you think of the surface wrapped option.

Inside the Car: I do like seeing that the air isn't going through the car.

Cheers

[sabaman]

Hi Royce

why do you find it good that air doesnt go in the car? the grill is open, it should.

I saved a pic of 320% res, not sure if you still need it?

Also, how do i do this surface wrap and maybe should i try if some other format than 3ds doesnt have this? i know that 3ds can force triangulation so maybe thats the issue here, im gonna try that other car first because if im correct it had the same issue but only on lower resolutions.

Sabino,...