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sture May 18, 2013 04:28

Forces and moments
 
Hi,

I am analyzing a body of revolution, 1.1 m long and 0.16 m diameter. I use the freestream boundary condition.

functions
{
forces
{
type forceCoeffs;
functionObjectLibs ( "libforces.so" );
outputControl timeStep;
outputInterval 25;

patches ( body ); // the <body> is a group of patches
pName p;
UName U;
rhoName rhoInf; // Indicates incompressible
log true;
rhoInf 1.225; // Redundant for incompressible
liftDir (0 0 1);
dragDir (1 0 0);
CofR (0 0 0); // Axle midpoint on ground
pitchAxis (0 1 0);
magUInf 10;
lRef 3; // Wing root cord
Aref 0.0707; // Estimated
}
}

However, I get very strange lift and drag results a an alfa of 0, 5 and 10 degrees. The drag values are reasonable, but the lift is very small.

I use the body-referenced coordinate system for lift and drag directions.

Are the lift and drag force supposed to be summed for all the pathches in the group <body>? The thing is, they do not. I have summed for all the patches manually and then the results matches wind tunnel results pretty good (for CFD results).

SS


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