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Difference between forceCoeffs function and Paraview force calculation

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Old   September 28, 2018, 08:33
Default Difference between forceCoeffs function and Paraview force calculation
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Aleksei
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Good afternoon everyone

I`ve run several cases in rhoSimpleFoam for calculation drag and lift coefficient. Function forceCoeffs was used for run-time post-processing. After I used Paraview to calculate Cl and Cd (only pressure component):
  • Generate surface normals;
  • Calculator => (p)*Normals_X/(0.5*rhoInf*(URef^2)*ARef);
  • Integrate variables.

Results:
forceCoeffs
Cd : 0.0239694 (pressure: 0.0181724 :confused: viscous: 0.00579704)
Cl : 0.260187 (pressure: 0.260349 viscous: -0.000162107)
Paraview
Cd : 0.0408192 :confused:
Cl : 0.257274


My forceCoeffs file:

forceCoeffs1
{
type forceCoeffs;

libs ("libforces.so");

writeControl timeStep;
timeInterval 2;

log yes;

patches ( "Wall.*" );
// rho rhoInf; // Indicates incompressible
rhoInf 1.225; // Redundant for incompressible
liftDir (0 1 0);
dragDir (-1 0 0);
CofR (-0.44347 0 0); // Axle midpoint on ground
pitchAxis (0 0 1);
magUInf 56;
lRef 0.94; // Wheelbase length
Aref 0.019; // Estimated
/*
binData
{
nBin 20; // output data into 20 bins
direction (1 0 0); // bin direction
cumulative yes;
}
*/
}

Also such differense observed when I run cases in simpleFoam. However, inequality was less then 5%.

Any thoughts? What is the reason of this inconsistency?
I would highly appreciate any advice!
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Old   October 1, 2018, 05:20
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Aleksei
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Problem was solved.

Thanks to this thread https://www.cfd-online.com/Forums/op...-paraview.html I find out that "point" values in paraview are created by interpolation. By changing attribute mode in calculator from "point data" to "cell data" I`ve got Cl and Cd in paraview equal to ones from forceCoeffs function.
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Old   June 9, 2021, 04:05
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damu
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Hi Aleksei,

Thanks for the thread. Can you help me calculate viscous drag using ParaView?
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