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-   -   Boundary condition for UDS (http://www.cfd-online.com/Forums/fluent/46449-boundary-condition-uds.html)

 Tong Wu October 30, 2007 08:15

Boundary condition for UDS

Hi:

Does anyone know how to difine zero normal gradient boundary condition for UDS? The boundary condition for the fluid is pressure outlet. The buildin options for UDS boundary are specific value and specific flux which are different from my case.

Any suggestions or examples are very appreciated. Thank you very much.

 pmechz February 7, 2016 16:28

I'm using UDS for simulation of mixing of two fluids (with concentration of 1 at one inlet and concentration of 0 at another inlet) but I dont know how can I specify uds in pressure outlet boundary condition?

 pakk February 8, 2016 10:02

Open the boundary condition and click 'UDS'. Where else? ;)

 pmechz February 9, 2016 17:43

Quote:
 Originally Posted by pakk (Post 584191) Open the boundary condition and click 'UDS'. Where else? ;)
i mean that which amount is appropriate for uds in pressure outlet ?;)

 pakk February 10, 2016 05:09

How did you find out which pressure is appropriate for the pressure outlet?

(What I mean to say: use the condition that your problem requires... If your problem requires a value of 0, use a value of zero. If your problem requires a flux of 0, use a flux of 0. We can not say that...)

 pmechz February 11, 2016 10:05

1 Attachment(s)
Quote:
 Originally Posted by pakk (Post 584485) How did you find out which pressure is appropriate for the pressure outlet? (What I mean to say: use the condition that your problem requires... If your problem requires a value of 0, use a value of zero. If your problem requires a flux of 0, use a flux of 0. We can not say that...)
my problem is the article that i am modeling just shows pressure outlet for outlet boundary condition. and said nothing about amount of user scalar.
i sent you the pic of my question location

 pakk February 11, 2016 10:14

Quote:
 Originally Posted by pmechz (Post 584686) my problem is the article that i am modeling just shows pressure outlet for outlet boundary condition. and said nothing about amount of user scalar. i sent you the pic of my question location
Your pictures shows that you are looking at the correct location. But I can not guess which boundary condition was used in the article that you are using. There are two 'standard' conditions:

1. Assume there is no scalar at this boundary, as if the boundary is completely 'clean'. In this case, set value to zero.
2. Assume there is equilibrium at this boundary, so there is no net flow of scalar across the boundary. In this case, set the flux to zero. (change "specified value" into "specified flux".)

But it is just as physical to set the value to "1.3712e-3" or the flux to "4.293e+2" or whatever values. It is just representing a different problem.

 pmechz February 11, 2016 10:37

Quote:
 Originally Posted by pakk (Post 584689) Your pictures shows that you are looking at the correct location. But I can not guess which boundary condition was used in the article that you are using. There are two 'standard' conditions: 1. Assume there is no scalar at this boundary, as if the boundary is completely 'clean'. In this case, set value to zero. 2. Assume there is equilibrium at this boundary, so there is no net flow of scalar across the boundary. In this case, set the flux to zero. (change "specified value" into "specified flux".) But it is just as physical to set the value to "1.3712e-3" or the flux to "4.293e+2" or whatever values. It is just representing a different problem.
sorry. may i have your private email to sent my article to you and help me more, if it's possible?
thanx

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