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Old   November 24, 2005, 10:44
Default periodic boundary condition
  #1
ousegui
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Hello I'm modelling flow in pipe, with CFX-5.7.1 It's a simpl case "poiseuil flow", but i want use a periodic boundary in one region, i didn't find this option How can I to resolve this probem thnx

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Old   November 24, 2005, 11:38
Default Re: periodic boundary condition
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matej
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hi,

I'm not sure I got the right picture of what you're trying to do... you have a domain, and want to have periodic BC on one 'side'? well you simply cannot as it really does not make sense.

the periodic BC are taking what goes out of the domain on one region and prescribe it as BC on the other side, simply put.

what is it you want to simplify in the model?

isn't it the symmetry BC you want to use?

matej
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Old   November 24, 2005, 12:04
Default Re: periodic boundary condition
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ousegui
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It's not a syymetry BC. perhaps iwasn't clear. But I want take what goes out of the domain on one region and prescribe it in the inlet region. So how can I do this. thnx
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Old   November 24, 2005, 13:47
Default Re: periodic boundary condition
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matej
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quite easilly, I guess. you do not create an inlet BC, but two periodic BCs. One for out , one for inlet. although I've used it with another software, not cfx.

if this would not work, you can try some user routine, i guess.

matej
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Old   November 25, 2005, 04:54
Default Re: periodic boundary condition
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matejk
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You should create a domain interface, then select periodic as interface type and select appropriate pathces for interface side 1 and 2.

I hope this helps
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Old   November 25, 2005, 04:55
Default Re: periodic boundary condition
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ousegui
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I'll try thnx
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Old   November 25, 2005, 04:59
Default Re: periodic boundary condition
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test
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Hi,

Step 1. go to Interfaces and create a periodic pair of the inlet an outlet. Specify it as translational periodicity.

You can then follow one of the following:

Step 2.a Specify an initial condition for velocity, pressure, turbulence kinetic engergy and turbulence energy dissipation.

or

Step 2.b. You can simlate the flow to be transient and secify both inlet as well as oulet as inlet boundary condition with similar values. Also need to include the expert parameter "build artificial walls=f". This seems a bit trickier though to set up.

I have simple example case files for this setup, but do not know how to load the same on the forum.

Regards, test
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Old   November 25, 2005, 05:05
Default Re: periodic boundary condition
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matejk
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one other thing.. You should include a momentum source term that will correspond to a pressure drop - this will drive the flow from inlet to outlet. If you would like to prescribe a certain mass flow rate, you will have to do some trial-and-error runs to prescribe appropriate pressure drop for wanted mass flow rate.

There already was some discussion about this in the forum, though.
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