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Force Coefficients Values NACA0015

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Old   March 11, 2020, 01:18
Default Force Coefficients Values NACA0015
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A P
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I am running simulation for 2D airfoil NACA0015 using simpleFoam. I am getting approximate half the values of Cl for various angle of attack. When I halve the value of area I get the correct result of Cl. I am confused what I am doing wrong. I am attaching condition for angle of attack 6 deg and Re10^5. Please guide me through it.
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 4.1 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

application simpleFoam;

startFrom latestTime;

startTime 0;

stopAt endTime;

endTime 4500;

deltaT 1;

writeControl timeStep;

writeInterval 50;

purgeWrite 0;

writeFormat ascii;

writePrecision 6;

writeCompression off;

timeFormat general;

timePrecision 6;

runTimeModifiable true;

functions
{
forces1
{
type forceCoeffs;
libs ("libforces.so");
writeControl timeStep;
writeInterval 1;
patches ( "AIRFOIL");
rho rhoInf
log true;
rhoInf 1.225;
liftDir (-0.104 0.994 0);
dragDir (0.994 0.104 0);
CofR (0 0 0);
pitchAxis (0 0 1);
magUInf 1.48;
lRef 1;
Aref 0.5;
}


}
// ************************************************** *********************** //
/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: 5 |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class volVectorField;
object U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions [0 1 -1 0 0 0 0];

internalField uniform (1.47 0.155 0);

boundaryField
{
AIRFOIL
{
type noSlip;
}
INLET
{
type fixedValue;
value uniform (1.47 0.155 0);
}
OUTLET
{
type zeroGradient;
}
TOP
{
type fixedValue;
value uniform (1.47 0.155 0);
}
BOTTOM
{
type fixedValue;
value uniform (1.47 0.155 0);
}
frontAndBackPlanes
{
type empty;
}
}

// ************************************************** *********************** //
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Old   July 7, 2020, 03:11
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You Wu
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Hi prakashPra,
Your problem may be caused by your grid. I think there may be something wrong with your force calculation;
Force coefficients are calculated by:
force/(0.5*rho*Aref*U^2)
However, the "force" is NOT calculated according to "Aref" in controlDict. It is decided according to your mesh. So even if the Aref is set to be the same as the experimental wing area, wrong forces will result in incorrect force coefficients.
You should pay attention to the thickness of your mesh. In 2D simulation, Your 2D mesh will be extruded into 3D mesh (the division in 3rd direction is 1). You should set the extruding length equal to the wing span, then you could get right forces and force coefficients.
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