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-   -   Torque or moment? (http://www.cfd-online.com/Forums/cfx/126153-torque-moment.html)

abrahamgx November 9, 2013 09:35

Torque or moment?
 
1 Attachment(s)
I am now calculating a HAWT in CFX. I monitor the torque_y()@blade and normal moment on blade(y) in solver manager, where y is the axis. I find that there is difference between them as in the figure.
How does it happen?Which one is the real shaft torque of HAWT?

http://www.cfd-online.com/Forums/att...1&d=1384004214

ghorrocks November 10, 2013 05:41

I am not certain but I suspect normal moment is the pressure force integrated over the surface. It does not include viscous forces. torque_y includes both pressure and viscous forces.

abrahamgx November 14, 2013 10:21

Quote:

Originally Posted by ghorrocks (Post 461384)
I am not certain but I suspect normal moment is the pressure force integrated over the surface. It does not include viscous forces. torque_y includes both pressure and viscous forces.

I wonder which one should I use? It seems that the normal moment which does not include the viscous forces is more consistent with the experimental results.

murx November 14, 2013 10:33

Quote:

Originally Posted by abrahamgx (Post 461980)
I wander which one should I use? It seems that the normal moment which does not include the viscous forces is more consistent with the experimental results.

Your experimental results probably include the viscous forces, so you should use torque_y for comparison if Glenn is right.

abrahamgx November 18, 2013 12:19

Quote:

Originally Posted by murx (Post 461985)
Your experimental results probably include the viscous forces, so you should use torque_y for comparison if Glenn is right.

OK. Thank you !

FrankS November 20, 2013 17:39

From my experience, CFD Post adds up the normal and tangential moments to get the total moment. The normal component represents the pressure contribution and the tangential component the viscous contribution to the total moment. Specifying an output monitor in CFD Pre as "torqure_y()@location" will output the total moment comprised of both the pressure and viscous contributions.


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