Openfoam fluxes problem
 

Hi everyone!,

I stepped into something that isn't clear at all and I hope that you can clarify some passages. I am solving an incompressible mrf problem with the simple alghoritm. Once the simulation is ended I wrote a postprocess script that evaluate the total pressure and the massflow at the inlet and outlet.
Here the problem: if I evaluate the flowrate using fvc::flux(U), where U is the velocity field given by openfoam, the continuity isn't respected and I have an higher flowrate at the outlet than at the inlet (70% higher!). Instead if I evaluate the flowrate by summing the phi field given by openfoam over the patch, the continuity is respected and the flowrates at inlet and outlet are equals.

I know that in the simple alghoritm I have a correction of the flux and then of the velocity, but I can't understand how it is possible that the results are different! The fvc::flux(U) must give the same field of phi and in general must satisfy the continuity equation, otherwise shoudn't be correct... Am I missing something? :( I tried also to not use fvc::flux() but to use interpolate(U) & mesh.Sf() but the results are the same...

Ps: My outlet boundary conditions are inletoutlet for velocity and fixed value for pressure. My inlet boundary conditions are fixed value for velocity and zeroGradient for pressure.