[Jack001]

My problem should be simple: The lift of an airfoil is always in the direction normal to the free stream, and drag is in the opposite direction. I need a way of automatically getting the direction of the free stream velocity vector that is specified in myCase/0/U and read this into my system/controlDict file which computes the coefficients below:

myLiftDirection= (-sin(alpha) cos(alpha) 0 )
myDragDirection= (cos(alpha) sin(alpha) 0)

where alpha is obtained from the boundary condition file of the inlet velocity.

forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (fixedWall);
// pName p;
// UName U;
rhoName rhoInf;
rhoInf 1000;
CofR (0 0 0);
liftDir myLiftDirection;
dragDir myDragDirection;
pitchAxis (0 0 0);
magUInf 0.05; // Free stream velocity
lRef 0.3; // Diameter of cylinder?
Aref 0.0707; // Ref. Area = cross sectional area?
outputControl timeStep;
outputInterval 1;
}