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deviation in calculated force between CFX solver and CFD post

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Old   April 9, 2014, 13:45
Exclamation deviation in calculated force between CFX solver and CFD post
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Max
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Hi,

in my simulations, I adjust certain boundary conditions every n-th timestep based on the torque acting on a body. Therefore I need to evulate this torque during my simulation. If I compare the torque shown in the solver manager for the last timestep to the torque shown in CFD post, there are significant deviations. My latest example:

torque_y_CF1@BODY (solver): 1.8 E-4 [Nm]
torque_y_CF1@BODY (post): -2.3 E-2 [Nm] (128 777 % deviation )

Can anybody explain this deviation?

I know that the torques are pretty low, so the absolute error is not very high. However, I need this accuracy for my investigation. I don't know if it's possible to say which one is closer to the physical reality, but at least having the _same_ "wrong" value in post and the solver would already help me.

Thanks
Max
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Old   April 9, 2014, 13:56
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Bruno
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Trust the values from the solver. They come directly from the momentum equations.

The values shown by Post are calculated from the available variables (pressure, for instance), and I think viscous forces aren't included.
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Old   April 9, 2014, 21:03
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Glenn Horrocks
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I understand the values calculated during the solver are from the control volume integration points, but the CFD-Post values are from the nodal values only. So the solver is using a higher resolution field to evaluate it and is more accurate.
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