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-   -   the air velocity is not zero on the wall? (http://www.cfd-online.com/Forums/cfx/24110-air-velocity-not-zero-wall.html)

Li Rong June 13, 2007 05:01

the air velocity is not zero on the wall?
 
Hi,guys. My case is very simple, the air was supplied from the left-top location and discharged from the right-bottom. And I did it in 2D.I did a simulation using k-e model in CFX, I set the wall boundary condition with no-slip, but I found the air velocity on the top wall is not zero when I post the result, but it is zero at the other wall including the left, right and bottom wall. And the simulation results conresponded with the expriment data well on the other part. I couldn't find the reason now. Is there something I set wrong? Thank you for any comments and suggestions!

with kind regards Li

Li Rong June 13, 2007 10:33

Re: the air velocity is not zero on the wall?
 
Please Contact the following websites to see the pictures.

1.velocity distribution at x=3m http://imageshack.dk//viewimage.php?...e/KZo45030.jpg

2. streamline http://imageshack.dk//viewimage.php?...e/ey545149.jpg

Robin June 13, 2007 11:43

Re: the air velocity is not zero on the wall?
 
Hi Li,

CFX constructs control volumes around the element vertices, so nodes on a wall have the values for the control volume next to the wall, which will have non-zero velocity. The control volume values are referred to as the "conservative" values. In your plot or in the variables list, you can opt to use the "Hybrid" values instead, which will use the actual boundary condition value.

Regards, Robin

Li June 13, 2007 11:56

Re: the air velocity is not zero on the wall?
 
Robin, thank you so much for your reply. I will try again.

With kind regards, Li

Li June 13, 2007 12:09

Re: the air velocity is not zero on the wall?
 
Yeah, I got the result that I want.


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