# how to sum force of the multi-element wing

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 July 20, 2013, 05:20 how to sum force of the multi-element wing #1 Member   Join Date: May 2010 Posts: 61 Rep Power: 9 Hi everyone, now I try to calculate the multi-element wing's force coefficient, there are one main wing and a flap , I use the function functions { forces { type forceCoeffs; functionObjectLibs ( "libforces.so" ); outputControl timeStep; outputInterval 1; patches ( wing_main wing_flap ); rhoName rhoInf; log true; rhoInf 1; CofR ( 0 0 0 ); liftDir (0 1 0 ); dragDir ( 1 0 0 ); pitchAxis ( 0 0 1 ); magUInf 10; lRef 1.0; Aref 1.0; } but the openfoam just output the last order patches value (here is flap), I can not get the total force acting on the wing. so anyone knows how to sum the force? thank you!

 February 3, 2014, 18:38 #2 Member   D L Join Date: Jun 2012 Posts: 36 Rep Power: 7 The ForceCoeffs library is a little weird when it comes to integrating on multiple BCs. I had success once when instead of using line breaks to delineate BCs, keep them on the same line and separate them by space. i.e. patches ( wing_main wing_flap ); A better approach is to be clever about your naming convention. In this case it's fairly simple; both of your BCs start with "wing_", therefore you can wildcard out the latter part of the names and have it integrate on anything that starts with "wing_" patches ( "wing_.*" ); The quotes are required for wildcards to work, and the .* is what initiates the wildcard. This wildcard approach can also be used in setting up multiple BCs with similar names and similar Boundary conditions (e.g. fixed no-slip walls) You can find an example for yourself in the tutorials. incompressible/simpleFoam/motorBike

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