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 Balder October 17, 2006 14:30

Neumann Pressure Boundary Condition with UDF

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.

Balder

 Souviktor June 1, 2009 12:57

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?

 san.pirate November 3, 2009 12:09

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.

 zahra.hosseini February 4, 2010 05:39

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.

 san.pirate February 4, 2010 10:44

Maintaining static pressure=0 will get you the neumann boundary condition.

I confirmed it with the Ansys CFX tech people.

thank you all..!

 behrang2009 August 24, 2010 14:20

I have the same problem with Temperature at the inlet for compressible flow.

 happy March 19, 2012 02:37

questions

Quote:
 Originally Posted by san.pirate (Post 244955) 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?:confused:
IDo you meant CFX or FLUENT?:rolleyes:

 Rahul123 June 25, 2012 05:43

I have written the UDF for convective B.C using DEFINE_PROFILE.....Can any1 tell me how to apply it at the outlet?

 highhopes July 6, 2012 11:21

Quote:
 Originally Posted by Rahul123 (Post 368152) 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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