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June 29, 2012, 08:59 
Forces for airfoil test case

#1 
New Member
Martin Vymazal
Join Date: Dec 2009
Posts: 16
Rep Power: 8 
Hello,
I would like to use the 'libforces.so' with simpleFoam to compute forces and force coefficients on an airfoil. I have several issues to which I didn't find answers in the documentation, so I hoped someone could be so kind and help me out. First, the airfoil consists of multiple parts, let's say surface1, surface2, surface3. Is there a way of listing on which surfaces the forces should be computed? I tried to set the following in the controlDict file: Code:
forces { type forceCoeffs; functionObjectLibs ( "libforces.so" ); ... patches (surface1,surface3); ... } Code:
airfoil_surfaces ( surface1; surface3; ); forces { type forceCoeffs; functionObjectLibs ( "libforces.so" ); ... patches ($airfoil_surfaces); ... } Second, I would like to get both forces AND force coefficients. Therefore I wrote: Code:
functions { forces { type forces; functionObjectLibs ( "libforces.so" ); ... } forces { type forceCoeffs; functionObjectLibs ( "libforces.so" ); ... } } Code:
# Time forces(pressure, viscous) moment(pressure, viscous) 500 (((5.55683 156.714 1.05751e18) (0.628621 0.13499 1.34059e19)) ((43.0962 1.52813 82.8966) (0.0371222 0.172871 0.000622457))) Finally, I would really like to compute the aerodynamic center of the airfoil. Is this possible with OpenFOAM? Thank you for every suggestion how to solve this. Best regards, Martin Vymazal 

July 2, 2012, 11:58 

#2  
Member
Joe
Join Date: Dec 2011
Location: Groton, CT
Posts: 67
Rep Power: 6 
Quote:
Have you tried different combinations? Such as a line for each surface? Or calling the forces function for each surface? I haven't done this before, so I'm not speaking from experience, I'm just thinking out loud. I believe that OpenFOAM spits out 4 sets of 3 values because it is the x, y, z pressure and viscous forces and moments. When you call the forces libraray you specify an origin and axis about which you calculate moments. If you have the moments and the axis location, you can set up a statics problem to calculate where your aerodynamic center is. 

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