CFD Online Discussion Forums

CFD Online Discussion Forums (
-   OpenFOAM Post-Processing (
-   -   how to sum force of the multi-element wing (

hewei July 20, 2013 06:20

how to sum force of the multi-element wing
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

{ forces


type forceCoeffs;

functionObjectLibs ( "" );

outputControl timeStep;

outputInterval 1;



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!

DLuo February 3, 2014 18:38

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
