Question about extracting volume averaged pressure value

Anna Tian · November 28, 2012, 03:56

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'?

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

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

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

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 < , 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

1. Take the equation of your cylinder, such as

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 < , 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.

November 29, 2012, 12:27		#6
brunoc Senior Member Bruno Join Date: Mar 2009 Location: Brazil Posts: 277 Rep Power: 21	1. Take the equation of your cylinder, such as 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 < , 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. CTYH likes this.

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November 28, 2012, 07:10		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	The image was not attached.

November 29, 2012, 05:03		#4
Lance Senior Member Lance Join Date: Mar 2009 Posts: 669 Rep Power: 22	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

November 29, 2012, 12:55		#8
brunoc Senior Member Bruno Join Date: Mar 2009 Location: Brazil Posts: 277 Rep Power: 21	They should be added as CEL Expressions. CFX has lots of tutorials that address how to use them.