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What is the formula for the frictional drag force in the "force" function?

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Old   August 1, 2024, 00:19
Post What is the formula for the frictional drag force in the "force" function?
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We use OpenFOAM v1806.
The "force" function is used to calculate the force.
When performing the "force" function, what is the equation used to determine the frictional drag force?
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Old   August 2, 2024, 13:43
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Check member function calcForcesMoments() in forces.C (https://www.openfoam.com/documentati...8C_source.html) ... it's all in there.
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Old   August 2, 2024, 21:33
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Thank you.
I have done the analysis with a laminar flow model.
Does the equation for viscous drag then depend on line 253 of force.c?
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Old   August 3, 2024, 09:53
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Very close - it's the section before that is used when a laminar turbulence model is selected:
Code:
    else if (foundObject<transportModel>("transportProperties"))
    {
        const auto& laminarT =
            lookupObject<transportModel>("transportProperties");
 
        const auto& U = lookupObject<volVectorField>(UName_);
 
        return -rho()*laminarT.nu()*dev(twoSymm(fvc::grad(U)));
... i.e. line 242 (same expression though!). This calculates the viscous stress, and then this is dot producted with the boundary face area vector on line 721:

Code:
const vectorField fV(Sfb[patchi] & devRhoReffb[patchi]);
to give the vector force.
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Old   August 4, 2024, 06:46
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Thank you very much.
I now have a better understanding of "force.c".
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