Different value of expression in CFD-Post and CFX-Solver

maciekstp · February 26, 2018, 08:37

Hello,
I defined an expression in CFX-Pre:
areaAve(Temperature)@REGION:My_Selection

It's defined on a mesh region (named selection from Meshing), but there is no a boundary condition in CFX on this specified mesh region (it's a part of bigger region with boundary condition - wall).

I set up this expression to monitor in Output Control. Then I ran the simulation and it's finished with good convergence. I checked value of expression in CFX-Solver (left click on plot trace in last iteration) - it shows 90,3 C. Next, I opened CFD-Post and checked my expression. Its value in CFD-Post is different than in CFX-Solver (88,4 C). What is the reason of this difference? And which value is calculated properly?

Best regards,

ghorrocks · February 26, 2018, 16:52

In the solver expressions are evaluated using integration point values. In CFD-Post expressions are evaluated using nodal values. The nodal values are a coarser network and should be less accurate, so the solver expression is more accurate.

Is the mesh on this region relatively coarse? You only get significant differences when the integration point values are different to the nodal values, and that usually only occurs on coarse meshes.

omididay@yahoo.com · February 28, 2018, 06:22

hi i have problem (Application Error in TurboGrid: ERROR Bladeset Count must be great

Antanas · March 1, 2018, 10:47

Quote:

Originally Posted by omididay@yahoo.com

hi i have problem (Application Error in TurboGrid: ERROR Bladeset Count must be great

Hello! I have problem too. Where can I buy some potatoes?

February 26, 2018, 08:37	Different value of expression in CFD-Post and CFX-Solver	#1
maciekstp New Member Join Date: Oct 2014 Posts: 5 Rep Power: 11	Hello, I defined an expression in CFX-Pre: areaAve(Temperature)@REGION:My_Selection It's defined on a mesh region (named selection from Meshing), but there is no a boundary condition in CFX on this specified mesh region (it's a part of bigger region with boundary condition - wall). I set up this expression to monitor in Output Control. Then I ran the simulation and it's finished with good convergence. I checked value of expression in CFX-Solver (left click on plot trace in last iteration) - it shows 90,3 C. Next, I opened CFD-Post and checked my expression. Its value in CFD-Post is different than in CFX-Solver (88,4 C). What is the reason of this difference? And which value is calculated properly? Best regards,

February 26, 2018, 16:52		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	In the solver expressions are evaluated using integration point values. In CFD-Post expressions are evaluated using nodal values. The nodal values are a coarser network and should be less accurate, so the solver expression is more accurate. Is the mesh on this region relatively coarse? You only get significant differences when the integration point values are different to the nodal values, and that usually only occurs on coarse meshes. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

February 28, 2018, 06:22	hi i have problem (Application Error in TurboGrid: ERROR Bladeset Count must be great	#3
omididay@yahoo.com New Member Mehdi Omidi Join Date: Feb 2018 Posts: 1 Rep Power: 0	hi i have problem (Application Error in TurboGrid: ERROR Bladeset Count must be great

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