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December 3, 2013, 16:15 
Force Function Calculator Ansys CFD Post

#1 
New Member
Sharad
Join Date: Dec 2013
Posts: 3
Rep Power: 3 
Hi guys,
My question is very basic. I read through the Ansys 14.5 manuals but it doesn't seem to answer my question so posting on here! I have a lorry model sat in a wind tunnel setup (Drawn on XY plane and extruded through Z axis). Now when I need to find the Drag Force on this lorry, I click on Function Calculator in CFD post and select the Z component for direction and it displays a force. My question is How does Ansys calculate this force? Does it use the generic Drag Equation = 0.5*rho*Usquared*Area? And if so what Area is it using? Is it all of the surface area of the lorry or just the cross sectional frontal area? Thanks in Advance! 

December 3, 2013, 18:03 

#2 
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,929
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No, it is not using drag=0.5*rho*A*U^2
It is integrating the pressure and wall shear over the surface of the body. 

December 3, 2013, 18:21 

#3 
New Member
Sharad
Join Date: Dec 2013
Posts: 3
Rep Power: 3 
Ah I'm guessing that equation originally comes from Navier stokes equations then. Will need to read into that stuff.
Forgot to mention that I have applied an inflation layer on the lorry. I calculated the boundary layer thickness and applied it as the inflation layer. But I'm guessing that with or without these layers that is how Ansys will always solve it? Thanks for the help!! 

December 3, 2013, 18:31 

#4 
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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Regardless of how you have meshed it it integrates over the surface. The meshing will "just" determine the accuracy of the simulation, not the approach.


December 3, 2013, 18:35 

#5 
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Sharad
Join Date: Dec 2013
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Thanks ever so much. Has made it clearer now!


January 30, 2014, 04:10 
I want find drag force and force of water axial turbine

#6 
New Member
Natthawut
Join Date: Jan 2014
Posts: 1
Rep Power: 0 
I want know value drag force and force at water turbine blade
The water axial turbine have eigth blade. I use Calculate Function in CFD Post (Ansys 13) result force in Program is much greater than the experimental result. Thank a lot, Natthawut 

January 30, 2014, 04:51 

#7 
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Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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August 14, 2014, 03:44 

#8 
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Cedric
Join Date: Jul 2014
Posts: 9
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Hello World,
if i calculate the force in any direction, is the answer the sum of pressure force and wall shear or only one of the components? 

August 14, 2014, 03:50 

#9 
New Member
Cedric
Join Date: Jul 2014
Posts: 9
Rep Power: 3 
i thin k i found the Answer by myself:
The force on a boundary is calculated using momentum flow data from the results file, if it is available. The result can be positive or negative, indicating the direction of the force. For nonboundary locators, an approximate force is always calculated. CFDPost calculates the approximate force as follows:


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cfd  post, force, function calculator 
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