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Anna Tian November 28, 2012 03:56

Question about extracting volume averaged pressure value
 
1 Attachment(s)
Hi,

May I ask, in cfx-post, how to extract the volume averaged pressure value of a cylinder shape volume(like in the attached picture) from my fluid domain?

Shall I still go 'Insert -> Location - Volume'?



http://www.cfd-online.com/Forums/dat...BJRU5ErkJggg==


Thank you very much!

ghorrocks November 28, 2012 07:10

The image was not attached.

Anna Tian November 29, 2012 04:25

Quote:

Originally Posted by ghorrocks (Post 394615)
The image was not attached.

The picture is already attached. It is just a small cylinder. And I only need to know the averaged pressure value in this volume. Thanks!

Lance November 29, 2012 05:03

A search in the manual on volume average would give you: volumeAve(<var|Expression>)@<Location>

In your case it would be something like volumeAve(Pressure)@cylinder

Anna Tian November 29, 2012 10:32

Quote:

Originally Posted by Lance (Post 394819)
A search in the manual on volume average would give you: volumeAve(<var|Expression>)@<Location>

In your case it would be something like volumeAve(Pressure)@cylinder

The problem is my fluid domain is not cylindrical. I need to put a cylinder there by myself so that I can extract only the value inside the cylinder. But how to put a cylinder into my fluid domain?

brunoc November 29, 2012 12:27

1. Take the equation of your cylinder, such as
x^2 + y^2 = r^2
2. Create an expression for the radius
radius = sqrt(x^2 + y^2)

3. Create a other expressions to check whether you're inside the cylinder:
insideCylinderZdir = if(radius < r, yourvariable, 0)
insideCylinder = if( zCylinderInf < z && z < zCylinderTop, insideCylinderZdir, 0 )
where 'zCylinderInf' and 'zCylinderTop' are the extreme positions of your cylinder in it's axial direction.

4. Create an expression to average 'insideCylinder' over your entire domain:
cylAve = volumeAve(insideCylinder)@domain
That should do it.

Cheers.

Anna Tian November 29, 2012 12:47

Quote:

Originally Posted by brunoc (Post 394887)
1. Take the equation of your cylinder, such as
x^2 + y^2 = r^2
2. Create an expression for the radius
radius = sqrt(x^2 + y^2)
3. Create a other expressions to check whether you're inside the cylinder:
insideCylinderZdir = if(radius < r, yourvariable, 0)
insideCylinder = if( zCylinderInf < z && z < zCylinderTop, insideCylinderZdir, 0 )
where 'zCylinderInf' and 'zCylinderTop' are the extreme positions of your cylinder in it's axial direction.

4. Create an expression to average 'insideCylinder' over your entire domain:
cylAve = volumeAve(insideCylinder)@domain
That should do it.

Cheers.


Where should I add these expressions?

brunoc November 29, 2012 12:55

They should be added as CEL Expressions. CFX has lots of tutorials that address how to use them.


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