topic Re: Getting rid of wall effects on a wind tunnel in CFD Forum

Getting rid of wall effects on a wind tunnel

Anonymous — Mon, 12 Apr 2021 06:09:36 GMT

Hello,

Ultimately I want to conduct a external flow analysis on my part, but I want to account for the floor which the External Volume tool within CFD doesn't allow for (the 5% gap would make my model have fluid volume surrounding all sides which is inaccurate). To get around this I created a wind tunnel in CAD (solidworks) and created the internal volume using void fill in CFD. Since I do not want the walls of the wind tunnel to be part of my analysis, I added slip boundary conditions to all walls. I did a coarse mesh to check how things are running, but it looks like wall effects are still being applied to my model (velocity is 0 at all walls, I've attached a picture that shows this).

Is my current set up the best way to set up my model for external flow analysis while still accounting for the floor of my model? How should I set up the boundary conditions of my wind tunnel walls to not get wall effects?

Re: Getting rid of wall effects on a wind tunnel

Anonymous — Mon, 12 Apr 2021 06:22:41 GMT

Noticed the .png might not be supported so I'm re uploading the photos as .jpg

Re: Getting rid of wall effects on a wind tunnel

marwan_azzam — Mon, 12 Apr 2021 11:07:31 GMT

Hello Julia,

The Slip/Symmetry boundary conditions should result in the velocity along those walls to be non-zero.

I'm not sure why they're zero. Can you share your model with us?
Please create a zip file of the model's support share file (*.cfz) and post it.

cheers,

Marwan

Re: Getting rid of wall effects on a wind tunnel

Anonymous — Mon, 12 Apr 2021 18:27:11 GMT

Hello Marwan,

Thanks for replying! Attached is the .cfz file.

Re: Getting rid of wall effects on a wind tunnel

marwan_azzam — Mon, 12 Apr 2021 22:56:21 GMT

Hello Julia,

You are applying Slip/Symmetry BCs to surfaces of Solid materials.

Suppress volumes 2, 3, 4, 5, & 6.

Actually volumes 3 and 6 don't make a difference but might as well since yo don't need them either.

cheers,

Marwan

Re: Getting rid of wall effects on a wind tunnel

Anonymous — Tue, 13 Apr 2021 08:07:26 GMT

That seems to have done the trick. Thank you!

Just for clarification, in the future if I was to go through this method, do I still need to apply slip boundary conditions on the suppressed geometries?

Re: Getting rid of wall effects on a wind tunnel

marwan_azzam — Tue, 13 Apr 2021 10:15:06 GMT

Hello Julia,

You are welcome. I'm glad it worked.

There is no need to apply any boundary conditions to suppressed geometry.

Marwan