[sepp.zell]

Dear community,

I want to solve a the flow through a porous medium with constant permeability. For the beginning I wanted to start with an easy test case and try to reproduce the pressure drop given by Darcy's law.
Therefore I choose a rectangular geometry with given inflow velocity (0.01 m/s) in x-direction and in the middle a porous medium with constant thickness (1 cm) and constant permeability (1e-10 m^2). The boundary conditions at the walls are chosen as symmetric in y-direction and as empty in z-direction.
As fluid I use water (rho=1000 kg/m^3, mu = 1 mPas).
For this setup (and the assumption of an one-dimensional flow), Darcy's law yields a pressure drop delta p of 1000Pa.

If I use the porousSimpleFoam solver from openFoam, the results are quite different depending on the number of discretization cells for the porous medium (the files you find attached).

I have the feeling that in the openFoam solution one discretization cell is missing. If the discretization cells are equistant, the pressure drop over all cells are the same. Thus Darcy's law yields for the pressure drop in one discretization cell 1000 Pa / N, where N is the number of cells. After some computations for different number of cells, I think that openFoam is just getting the pressure drop of N-1 cells thus, the result from openFoam is (N-1)/N*1000 Pa.
Let me illustrate this with a few numbers from my computations:



Since I am just started with openFoam, I am not sure, if I did something wrong. Therefore I attached my files. Maybe someone can tell me, if they are correct.
If my results would be correct, is there some bug in openFoam for this example? Is openFoam neglecting or forgetting about one cell? Is this in some way related to some interpolation scheme?

If some more data are needed, please tell me.

Thank you in advance for your answers and your help.

Regards

Sebastian