How to read results values on nodes?

Felipe Matos · February 24, 2010, 21:07

Hi
I'm starting at the Ansys CFX and i would like to know how to read the results at a specifc node. I've tried use the command "cfx5interp" at the command line (windows) but a message apeared that this a invalid command. Is there any way I can read this values inside the CFX-Post?

Thanks

ghorrocks · February 25, 2010, 00:41

Use a command editor launched off the CFX launcher. Then it will have the paths to the executables in it. If you use a normal commadn window you have to specify the full path to the executables.

Felipe Matos · February 26, 2010, 12:16

I managed to usa the interpolator correctly thanks.
But I wonder if there is another command that i can choose the node itself, like node #14, and see the results, instead choose a location (x,y,z). Does this command exist?

ghorrocks · February 28, 2010, 17:46

Why do you want a specific node rather than a location?

Felipe Matos · February 28, 2010, 21:18

Cause i want to make sure that the condition that i'm aplying in a boundary, like pressure, is really being followed.

My problem is this: i'm simullating a simple cylindrical pipe (2m diameter, 20m lenght). I'm putting a velocity condition in the inlet (a very low value for laminar regime), pressure condition at the outlet (0 Pa - absolute pressure) and no slip wall. The problem is: when I see the results, the pressures at the outlet ARE NOT 0 Pa as I commanded as boundary conditions - they are different from 0, and even negative (impossible, cause I'm working with absolute pressures). That's why I wanted to make sure that the nodes at the outlets were zero Pa, but I think they are not.

Should I create a new topic for this problem?

ghorrocks · February 28, 2010, 23:06

Have a read of the documentation. The default behaviour for an outlet is to define the total pressure for flow exitting the domain. This will mean the static pressure will be less than your specified pressure.

Also be aware that some boundary options use pressure averaging over the surface. This can also make the pressure vary over the patch.

And finally a zero absolute pressure condition cannot exist. It works in incompressible flow where the pressure can do whatever it likes - pressure is unbounded so it can go as negative as it wants.

February 26, 2010, 12:16		#3
Felipe Matos New Member FM Join Date: Feb 2010 Posts: 14 Rep Power: 16	I managed to usa the interpolator correctly thanks. But I wonder if there is another command that i can choose the node itself, like node #14, and see the results, instead choose a location (x,y,z). Does this command exist? Last edited by Felipe Matos; February 27, 2010 at 16:57. Reason: managed correctly the interpolator, thanks

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February 24, 2010, 21:07	How to read results values on nodes?	#1
Felipe Matos New Member FM Join Date: Feb 2010 Posts: 14 Rep Power: 16	Hi I'm starting at the Ansys CFX and i would like to know how to read the results at a specifc node. I've tried use the command "cfx5interp" at the command line (windows) but a message apeared that this a invalid command. Is there any way I can read this values inside the CFX-Post? Thanks

February 25, 2010, 00:41		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Use a command editor launched off the CFX launcher. Then it will have the paths to the executables in it. If you use a normal commadn window you have to specify the full path to the executables.

February 28, 2010, 17:46		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Why do you want a specific node rather than a location?

February 28, 2010, 21:18		#5
Felipe Matos New Member FM Join Date: Feb 2010 Posts: 14 Rep Power: 16	Cause i want to make sure that the condition that i'm aplying in a boundary, like pressure, is really being followed. My problem is this: i'm simullating a simple cylindrical pipe (2m diameter, 20m lenght). I'm putting a velocity condition in the inlet (a very low value for laminar regime), pressure condition at the outlet (0 Pa - absolute pressure) and no slip wall. The problem is: when I see the results, the pressures at the outlet ARE NOT 0 Pa as I commanded as boundary conditions - they are different from 0, and even negative (impossible, cause I'm working with absolute pressures). That's why I wanted to make sure that the nodes at the outlets were zero Pa, but I think they are not. Should I create a new topic for this problem?

February 28, 2010, 23:06		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Have a read of the documentation. The default behaviour for an outlet is to define the total pressure for flow exitting the domain. This will mean the static pressure will be less than your specified pressure. Also be aware that some boundary options use pressure averaging over the surface. This can also make the pressure vary over the patch. And finally a zero absolute pressure condition cannot exist. It works in incompressible flow where the pressure can do whatever it likes - pressure is unbounded so it can go as negative as it wants.