forceCoeffs and rhoInf dependency
I have an incompressible simpleFoam solution of a flow field. I use forceCoeffs to calculate Cd etc. on some patches.
Is there some bug in OF 2.1.1 or a bug in my understanding of physics?
Force on a patch is F=p*A, drag coefficient is Cd = F / (0.5 rhoInf U^2). Why is there no influence of rho?
if the solver is incompressible, the pressure computed by OpenFOAM is p/rho and not p.
Hence, you don't need to know the density to get your coefficient (just divide your pressure force by 0.5*Ue^2 A). :)
You can write anything you want for the density in forceCoeffs, it is not read when computing the coefficients.
Yeah, that became clear after posting this.
But I'm still riddled why OF requires setting a value of rhoInf. In the source code, as far as I can tell, it's determined by units if p' = p/rho (incompressible) or p' = p.
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