turbine force_y vs dP * area

Светлана · May 3, 2019, 00:02

In ansys 19.2 the built in function

force_y()@turbine Default

and a similar manual calculation (here 'top' and 'bottom' are circular surfaces below and above the turbine)

(areaAve(Pressure)@bottom - areaAve(Pressure)@top ) * area()@top

give different results 2-3 times, inconsistently in different cases as it is not a linear relationship. Is this a known issue? How do I troubleshoot this? Can attach a small test case if anyone is interested.

ghorrocks · May 3, 2019, 02:26

your areaAve functions just average the pressure over the surface, they do not take into account direction. The force_y function only gets the force in the y direction. So your function is not working out the force in the y direction.

Светлана · May 3, 2019, 02:31

In this case my calculations should give larger values than CFX's force_y,
because they do not multiply by cos (direction angle) in each point.
However in my case the "dP * area" calculation gives results which are 0.3 to 0.7 of the force_y value predicted by CFX.

ghorrocks · May 3, 2019, 02:34

If you want us to help you, you are going to have to post an image of what you are analysing, a description of what the top and bottom surfaces are and a plot of the pressure distribution.

May 3, 2019, 00:02	*turbine force_y vs dP area**	#1
Светлана Senior Member Svetlana Tkachenko Join Date: Oct 2013 Location: Australia, Sydney Posts: 407 Rep Power: 14	In ansys 19.2 the built in function force_y()@turbine Default and a similar manual calculation (here 'top' and 'bottom' are circular surfaces below and above the turbine) (areaAve(Pressure)@bottom - areaAve(Pressure)@top ) * area()@top give different results 2-3 times, inconsistently in different cases as it is not a linear relationship. Is this a known issue? How do I troubleshoot this? Can attach a small test case if anyone is interested.

May 3, 2019, 02:26		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,723 Rep Power: 143	your areaAve functions just average the pressure over the surface, they do not take into account direction. The force_y function only gets the force in the y direction. So your function is not working out the force in the y direction. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

May 3, 2019, 02:34		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,723 Rep Power: 143	If you want us to help you, you are going to have to post an image of what you are analysing, a description of what the top and bottom surfaces are and a plot of the pressure distribution. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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May 3, 2019, 02:31		#3
Светлана Senior Member Svetlana Tkachenko Join Date: Oct 2013 Location: Australia, Sydney Posts: 407 Rep Power: 14	In this case my calculations should give larger values than CFX's force_y, because they do not multiply by cos (direction angle) in each point. However in my case the "dP * area" calculation gives results which are 0.3 to 0.7 of the force_y value predicted by CFX.