[mali_anttho]

I am modeling flow through a porous medium where it is possible to take a representative volume element without any loss of generality and is a common practice. Hereby, I need to define periodic boundary conditions. The element under investigation is a perfect cube or cuboid with six faces, each parallel face forming a periodic pair. The interior has two zones, one normal fluid and the other porous medium. That being said, I have the following questions.

1. Is it possible or recommended to define periodic boundary conditions on all the six faces at the same time? Alternatively, one or more boundary conditions should be of a different kind like pressure/velocity inlet/outlet etc.

2. How much is it different defining them as an interface with periodicity or an actual periodic boundary condition with periodic and shadow faces? For the later, the mesh should match exactly on both the faces.

3. Any comment about the pressure gradient or the mass flow rate?

Any help is appreciated,

Ali