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Neumann Pressure Boundary Condition with UDF

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Old   October 17, 2006, 15:30
Default Neumann Pressure Boundary Condition with UDF
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Balder
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Dear all, I wonder if someone is able to give me an UDF coding example to force a Neumann b.c. to the pressure field on a pressure outlet, I mean:

dp/dn = 0 where n is the normal of a "pressure outlet" b.c.

Thanks for your attention.

Balder
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Old   June 1, 2009, 13:57
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souviktor
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Hello,

I am stuck with the same problem except the fact that I want to implement du/dx=0 for a laminar pipe flow at the outlet(fully developed condition).

Have you got any work around for your problem so far?
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Old   November 3, 2009, 12:09
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Even I've the same problem, haven't got much help, how about you guys. The average static pressure=0 is the nearest matching BC. But I am not sure whether it serves any purpose.
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Old   February 4, 2010, 05:39
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Why do'nt you use an outflow bc (if u dont have backflow)? this bc sets both dp/dn=0 and dv/dn=0 automatically. if you have backflow through your boundary, then these Boundary Conditions make the problem ill-posed.
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Old   February 4, 2010, 10:44
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Maintaining static pressure=0 will get you the neumann boundary condition.

I confirmed it with the Ansys CFX tech people.

thank you all..!
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Old   August 24, 2010, 15:20
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Behrang Asgharian
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I have the same problem with Temperature at the inlet for compressible flow.
adiabatic: dT/dx=0
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Old   March 19, 2012, 03:37
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Quote:
Originally Posted by san.pirate View Post
Maintaining static pressure=0 will get you the neumann boundary condition.

I confirmed it with the Ansys CFX tech people.

thank you all..!
So what about K, zitha and temp.?does P=0 covers all variables?
IDo you meant CFX or FLUENT?
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Old   June 25, 2012, 06:43
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Satish Gupta
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I have written the UDF for convective B.C using DEFINE_PROFILE.....Can any1 tell me how to apply it at the outlet?
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Old   July 6, 2012, 12:21
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Quote:
Originally Posted by Rahul123 View Post
I have written the UDF for convective B.C using DEFINE_PROFILE.....Can any1 tell me how to apply it at the outlet?
Do you mean a convective boundary condition for a scalar value? By scalar value I mean temperature, species mass fraction or user defined scalar. If so, You can define both the value itself and the derivative with respect to the normal direction to the surface. Firstly, of course you need to compile or interpret it. Then you will see the name of your udf at the relevant boundary condition panel.
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