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-   -   New Variable in CFX Post (http://www.cfd-online.com/Forums/cfx/26301-new-variable-cfx-post.html)

Ben August 24, 2008 21:55

New Variable in CFX Post
 
Hi,

I'm trying to create a new vector variable in CFX post. (velocity * vorticity). However, I can't get to assign the new variables. Does anyone know how to assign a new variable dependent on existing variables?

Cheers, ben

frank August 24, 2008 22:35

Re: New Variable in CFX Post
 
you can try the following:

1. cfx-post, click variable table, then right click > new>name. 2.select the method= expression >vector. 3. input you definations. 4.a user defined variable will appear under the variable table.

John S. August 25, 2008 11:16

Re: New Variable in CFX Post
 
Another method would be to create and expression in Post defined as Vorticity * Velocity and then simply create a variable that references that expression.

For example, when I run my CFD I usually create an expression for the reference pressure, Pref, which I subtract off from the value I set at pressure specified inlets/outlets. When I post process and want to calculate the absolute total pressure, I create an expression (usually called ptpsi or something) and define it simply as Total Pressure + Pref. I then create a new variable called PT abs and reference it to the expression ptpsi. That way when I want to do any calculations or contours involving total pressure I can specify my new PT abs variable and not have to do any manual pressure corrections.


CycLone August 26, 2008 16:28

Re: New Variable in CFX Post
 
Did you want Vorticity times Velocity or Vorticity dot Velocity? For the latter you need to write expressions for each component.


Ben August 28, 2008 22:47

Re: New Variable in CFX Post
 
Thanks for the reminder.. I am interested in vorticity 'cross' velocity. Does this mean that I will have to write the expression for each of the component in ANSYS? Or does ANSYS CFX instantly recognize in the expression function that: vector x vector = "cross product of vectors"?

CycLone August 29, 2008 16:18

Re: New Variable in CFX Post
 
Post doesn't currently do vector arithmetic, so you need to input the expressions. Which isn't really much work, we've already done more typing in this discussion alone!

Ben September 1, 2008 00:37

Re: New Variable in CFX Post
 
Ok, cheers for the input!

pritam1688 March 27, 2012 09:35

Create expression in CFD-Post
 
I am trying to create a new expression in cfd-post for Nussult number i.e

Nu = h*d / k
But not succeded,i done with heat transfer coefficient i.e 'h' at perticular interface but not with 'Nu'

please help

ghorrocks March 27, 2012 17:48

Have a look in the CFX tutorials, I know some of them define post-processing variables. That will show you how to do it.

soni_sth June 20, 2012 18:10

Hi Ghorrocks,

How can we define variables in CFX post? You mentioned its in tutorials but I found defining variable in CFX pre. Is there a way to define in post?I have to plot the contour of pressure coefficient at the mid span of turbine blade.

I would really appreciate your help

Thanks


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