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-   -   Pressure as the variable in Expression in CFX-Pre (http://www.cfd-online.com/Forums/cfx/20996-pressure-variable-expression-cfx-pre.html)

Atit Koonsrisuk February 16, 2005 14:42

Pressure as the variable in Expression in CFX-Pre
 
Please someone suggest me how to use 'Pressure' and 'area' at a certain face inside the domain as the variable in 'Expressions' of CFX-Pre.

I would like to define one variable in 'Expressions' of CFX-Pre as the function of the pressure at one certain face of my domain. I found the name of face is F5.B1.P3 and the formula is the pressure at that face times face area. However I do not know how to define that pressure. I already tried:

Pressure@F5.B1.P3 and Pressure()@F5.B1.P3 and Pressure("F5.B1.P3") and massFlowAve(Pressure)@F5.B1.P3

but none of them is acceptable. Do anyone know how to define the pressure at certain face in 'Expressions'

In addition, Function Calculator in CFX-Post can compute 'area' at any face, so there must be 'area' as the parameter in CFX, isn't it? However I have no idea how to get 'area' to use in CFX-Pre. I have tried:

area@F5.B1.P3 and area()@F5.B1.P3

they all doesn't work. In my domain, there are some 2D regions that I specify the boundary conditions. For example, I have 'in' as the 2D region for 'Inlet' boundary condition. I have tried

area@in

CFX accept this definition, but the preprocessor does not support its evaluation in CFX-Pre. Do I have to define F5.B1.P3 as the 2D region? I think that we define 2D region for specifying boundary conditions, while this face is the face on fluid subdomain for energy source, which need not any boundary condition. So I think specify it as 2D region is not right, isn't it?

Thank you very much for your kind consideration.

Atit

Juan Carlos February 16, 2005 14:55

Re: Pressure as the variable in Expression in CFX-
 
Hi,

The callback functions within CFX-Pre and the CFX-Solver only support the use of regions that are defined as : domain, sub-domain, boundary, domain interfaces, point sources or monitor points. There is no mechanism for accessing a face that is not a boundary or a domain interface.

Can you make that region a domain interface? and treat the subdomain as a domain?

For further information, you can look at the CEL Variables, Functions and Constants section of the CFX-5.7/5.7.1 documentation.

Regards, Juan Carlos


Atit Koonsrisuk February 16, 2005 15:09

Re: Pressure as the variable in Expression in CFX-
 
Dear Carlos, Thank you very much for your kind answer.

I follow your suggestion by defining that face as the domain interface named 'ADin'. As I stated earlier that

area@in

do work, but

area@ADin

doesn't work. Why?

In addition, do you have idea how to use pressure, because even

Pressure@in

doesn't work

Thank you very much.

Atit

Juan Carlos February 16, 2005 16:18

Re: Pressure as the variable in Expression in CFX-
 
Hi,

When you refer to the domain interface, you should refer to a side of it. Then, you really refer to the boundary on the side you are interest in. I think that will solve the area@ADin problem..

Second, callbacks are single value functions.. You cannot access the Pressure array on a boundary via a callback yet.. You can average, min, max the array but not access the array itself.. You may be confused with the syntax, for example area is a function not a variable with syntax area@location. Other example is areaAve(variable, like Pressure)@location.

For example, to obtain the area integral of Pressure over a surface, you do : areaInt(Pressure)@location

Regards, Juan Carlos



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