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jtipton2 August 12, 2010 08:10

Specify hybrid values for expressions in CFX-Post?
When creating expressions in CFX-Post, is it possible to force a hybrid calculation?

This question stems from my desire to calculate an average Nusselt number on the top surface of the outlet of a rectangular channel. To obtain the average heat flux I am using the following expression:

lengthAve(Wall Heat Flux)@TopLineOut

Here's the problem...
  • If I open a result in CFX-Post and double click on my expression, I get a very large number (1.#INF [W m^-2]).
  • If I next go to the calculator and calculate "lengthAve(Wall Heat Flux)@TopLineOut" I first get the result "Undefined".
  • By pressing the "Hybrid" button, a reasonable value is then displayed.
  • Finally, if I then go back to the expressions tab and click on my custom expression, the reasonable value is displayed and any other custom expressions that use a hybrid variable suddenly display reasonable numbers also.
Does anyone have an idea what is happening? This is very annoying and keeps me from using the Workbench parameter study feature.

ghorrocks August 12, 2010 18:36

Hybrid/conservative value thing does not apply to surface integrals on boundary faces, but you are trying to do a line integral I assume on a boundary face. What I would consider doing is to replace your line integral with a surface integral where the surface you are integrating over is thin, so it is just about a line anyway. Then you evaluate the area integral and that should work fine.

topsedar July 20, 2013 03:58

in CFX post go to:
Calculations ==> Function Calculator
then set your request. For example lengthAve(Wall Heat Flux)@TopLineOut

then at the bottom of Function Calculator tab, Press Hybrid button.
after this CFD Post automatically uses Hybrid Values For your Expression :)

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