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Changing magUInf does not affect lift calculation

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Old   October 8, 2022, 04:27
Question Changing magUInf does not affect lift calculation
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I am currently simulating a s1223 airfoil and want to test it at different speeds. My first test was with magUInf = 22.22 and this was the result for the lift: -112,908 N
So the second try was to change the magUInf in the forceCoeffs file to 36.11. After running everything again I still get the same lift of -112,908 N. Is there something that I am missing?

I run:

mpirun -np 8 snappyHexMesh -overwrite -parallel
reconstructParMesh -constant
rm -rf processor*
rm -rf 0
mv 0.orig 0
mpirun -np 8 simpleFoam -parallel
reconstructPar -latestTime

My calculation is done in Paraview using GenerateSurfaceNormals and calculate the force with

and using IntegrateVariables of course.

My forceCoeffs file looks like that:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2206                                 |
|   \\  /    A nd           | Website:                      |
|    \\/     M anipulation  |                                                 |

    type            forceCoeffs;

    libs            (forces);

    writeControl    timeStep;
    timeInterval    1;

    log             yes;

    patches         (clio3rs);
    rho             rhoInf;      // Indicates incompressible
    rhoInf          1;           // Required when rho = rhoInf
    liftDir         (0 0 1);
    dragDir         (1 0 0);
    CofR            (3.5 0 0);  // Axle midpoint on ground
    pitchAxis       (0 1 0);
    magUInf         22.22;        // 80 km/h
    lRef            0.2;        // chord length 
    Aref            0.28;        // Aref=(airfoil chord length)*(length in the spanwise direction of your 2D domain)

    type                    binField;
    libs                    (fieldFunctionObjects);
    binModel                singleDirectionUniformBin;
    fields                  (forceCoeff);
    patches                 (clio3rs);
    decomposePatchValues    true;
    CofR                    ${..forceCoeffs1.CofR};

        nBin        20;          // output data into 20 bins
        direction   (1 0 0);     // bin direction
        cumulative  yes;
    writeControl            timeStep;

// ************************************************************************* //

Any ideas?

Thank you!

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Old   October 10, 2022, 05:27
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Hi Marius,

forceCoeffs is used to compute aerodynamic coefficients (drag coefficient Cd, lift coefficient Cl, etc...) in a file in the postProcessing directory. It does not have any effect on the simulation, it is only a post-processing function. You can also use the forces function object to report forces right from OpenFOAM instead of computing it in ParaView.

If you want to change the flow velocity in the simulation, you need to update the velocity boundary condition in 0/U file.

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Old   October 10, 2022, 05:29
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Hi Yann,

thanks a lot for your answer. I just updated the U file and now everything is fine.

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airfoil, forcecoeffs, lift and drag, maguinf

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