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Boundary condition for UDS

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Old   October 30, 2007, 08:15
Default Boundary condition for UDS
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Tong Wu
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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.
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Old   February 7, 2016, 16:28
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would you please help me?
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?
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Old   February 8, 2016, 10:02
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Open the boundary condition and click 'UDS'. Where else?
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Old   February 9, 2016, 17:43
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Quote:
Originally Posted by pakk View Post
Open the boundary condition and click 'UDS'. Where else?
i mean that which amount is appropriate for uds in pressure outlet ?
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Old   February 10, 2016, 05:09
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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...)
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Old   February 11, 2016, 10:05
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Quote:
Originally Posted by pakk View Post
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
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Old   February 11, 2016, 10:14
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Quote:
Originally Posted by pmechz View Post
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.
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Old   February 11, 2016, 10:37
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Quote:
Originally Posted by pakk View Post
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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