Forces & Torque in CFX-Post

Typhoon · September 13, 2013, 07:15

Hi all,
I have found in CFX user guide (12.0) following information :
*******

CFD-Post calculates the approximate force as follows:

If the locator is a wall boundary, the force is equal to the pressure force.
For all other locators, the force is equal to the pressure force plus the mass flow force (due to the advection of momentum).
In all cases, if wall shear data exists in the results file, the viscous force is added to the calculated force.

******
From this text it is not clear whether the viscose force is included or not in the case when the locator is wall boundary and shear data exists in the result file.
I need to calculate torque acting on a blade. CFX-solver (final report in out file) and Post (function calculator)give completly different torque on the same wall (blade).
Do yo know what can be the reason? Is it the absence of viscose component in Post? If yes, how to calculate in Post correct torque?
Best regards

ghorrocks · September 13, 2013, 08:40

My understanding is the force includes both pressure and viscous components. But to be sure I would do a little demo case (maybe flow over a plate parallel and perpendicular to the flow) and check the numbers are what you expect.

September 13, 2013, 07:15	Forces & Torque in CFX-Post	#1
Typhoon New Member Join Date: Dec 2010 Posts: 9 Rep Power: 16	Hi all, I have found in CFX user guide (12.0) following information : ***** CFD-Post calculates the approximate force as follows: If the locator is a wall boundary, the force is equal to the pressure force. For all other locators, the force is equal to the pressure force plus the mass flow force (due to the advection of momentum). In all cases, if wall shear data exists in the results file, the viscous force is added to the calculated force. **** From this text it is not clear whether the viscose force is included or not in the case when the locator is wall boundary and shear data exists in the result file. I need to calculate torque acting on a blade. CFX-solver (final report in out file) and Post (function calculator)give completly different torque on the same wall (blade). Do yo know what can be the reason? Is it the absence of viscose component in Post? If yes, how to calculate in Post correct torque? Best regards

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September 13, 2013, 08:40		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	My understanding is the force includes both pressure and viscous components. But to be sure I would do a little demo case (maybe flow over a plate parallel and perpendicular to the flow) and check the numbers are what you expect.