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Lift & Drag calculation help

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Old   November 27, 2018, 11:19
Default Lift & Drag calculation help
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kevin
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Hi, everyone

I am a new man of openfoam. Recently day I was running the naca0012 airfoil case by openfoam. I realized the lift & drag calculations in the system/controlDict file. The details are as follows
Howerever, these calculations can not get correct results of Cl (lift) and Cd (drag). They are about 1e-7, too small.

Is there any error in the folllowing functions? Could anyone help me? Thanks.
__________________________________________________ _______________

// *** calculate force coefficients *** //
functions
{
forceCoeffs
{
type forceCoeffs;
functionObjectLibs ("libforces.so");
patches (wall);
log true;
rho rhoInf;
rhoInf 1.29;
CofR (0 0 0);
liftDir (0 1 0);
dragDir (1 0 0);
pitchAxis (0 0 1);
magUInf 250;
lRef 1;
Aref 1;
writeControl timeStep;
writeInteval 100;
}
};
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Old   November 28, 2018, 04:04
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Zander Meiring
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Force calculation is correct. Any error is more likely a result of improper modelling/solving. 1e-7 is a very small error though
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Old   November 28, 2018, 10:59
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Quote:
Originally Posted by yambanshee View Post
Force calculation is correct. Any error is more likely a result of improper modelling/solving. 1e-7 is a very small error though
Thank you. But the values of Cl and Cd are as small as 1e-7. They are unphysical.
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Old   November 29, 2018, 02:40
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Zander Meiring
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It would be helpful if you can include at what conditions you are testing. See this sticky post on the forum.



Based on the coefficient function attached, I would assume that your inlet velocity is 250 m/s and that your blade chord length 1 m. Is this correct?
Are you running a 3d case; and in which case, what is the thickness of the domain?

What is your viscosity?
What is your mesh like?
What is the rough dimensions of your domain?
How many iterations have you done (and how converged is your flow field
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