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Boundary Condition in CFX

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Old   January 30, 2011, 04:30
Default Boundary Condition in CFX
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Ricky Chen
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Hi all,

I'm trying to make a water intake model in CFX. The inlet boundary condition is normal speed = 2m/s and I set the outlet condition as static pressure = Pres (where Pres is the water pressure due to gravity) (Please see the first picture for details). To simulate the gravity effect on the water, I added a sub-domain with general momentum source.

The result seems fine (please see the second diagram). But when I tried to change the inlet boundary to 0.2 m/s, the model starts to have problem with convergence. And the result doesn't make sense at all, especially the streamline from outlet (see third diagram). I'm thinking that there is something wrong with the outlet boundary condition, but I'm not sure where it is.

It would be great if anyone can provide some advices. Any suggestions would be welcome.

Thanks in advance!!

Ricky Chen
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File Type: jpg Model.jpg (49.3 KB, 9 views)
File Type: jpg 3_001.jpg (85.6 KB, 12 views)
File Type: jpg 4_001.jpg (79.0 KB, 9 views)
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Old   February 1, 2011, 20:43
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Hi Ricky,

Unless I am mistaken with what you are trying to achieve, you should be able to set Buoyancy by double clicking on the domain and its on the first tab.

Set the value for buoyancy in the direction that you want it.

Then just set the outlet pressure at 0 (relative static pressure) and CFX will work out the hydrodynamic pressure for you.

There should be a tutorial for something similar in the help menu that you can look at, or even search for buoyancy under help and you'll find heaps of info.

Hope this helps!


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