[sven]

Hi,

I am simulating a turbulent flow around a square. For This flow, I want to calculate the lift and the drag coefficients CD and CL. By scanning through posts in this forum, I found that this is possible by adding the following lines to the controlDict file:

functions
(
forces
{
type forces;
functionObjectLibs ("libforces.so"); //Lib to load
patches (cylinder); // change to your patch name
rhoInf 1.204; //Reference density for fluid
CofR (0 0 0); //Origin for moment calculations
outputControl timeStep;
outputInterval 100;
}

forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (cylinder); //change to your patch name
rhoInf 1.204;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 0);
magUInf 0.1;
lRef 1;
Aref 1;
outputControl timeStep;
outputInterval 100;
}
);

Unfortunately this does not yield the expected values for CL and CD. For fixing this problem and obtaining the correct CL/CD I first need some information on the code posted above:

1. rhoInf: What is the reference density? The density in my free stream?
2. What is magUInf? How can i determine/calculate this value?
3. The program seems to use "libforces.so". I could find this file, but where can I find the corresponding source code?
4. Where are the equations for calculating CD and CL defined?

I appreciate your help. Thank you very much