forceCoeffs and rhoInf dependency
Hello,
I have an incompressible simpleFoam solution of a flow field. I use forceCoeffs to calculate Cd etc. on some patches. Code:
coeffsCar 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? Thanks! |
Hi Florian,
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. Regards, Joachim |
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. Regards... |
hi Joachim,
I want to ask you how to calculate the value of Cd and Cl ? by calculating it by dividing pressure force by (0.5*v*v*A),so this mean that results of openfoam for cd and cl are not correct ? |
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