I am working on a simple 3D porous media problem, where fluid flows from a pipe through a porous (distributed resistance region). I would like to know what the boundary condition is, at the interface of the liquid- porous region.
The simCFD manual says that the boundary conditions at the interface are automatically assigned by the software, but for the purpose of documentation, I would like to know what the bc's are.
Any help would be highly appreciated.
It really depends on how you are modelling. From what I understand, following is the scenario at the interface:
1) When volume resistance is used: In this case, probably the momentum sink (negative pressure gradient) of the porous region will kick in to contribute in momentum equations.
2) When surface resistance is used: In this case, a definite pressure drop is obtained locally, depending on the local velocities and the resistance coefficients defined only in the normal direction. This, I am told, is just an arithmatic adjustments of the pressure and related properties across the surface and no sinks in NS equations are involved. Additionally, it will direct all the outgoing velocities from the surface perpeindicular to it. Thus this method comes with caveats that are mentioned in the doco.
Hope this helps?
Thanks for your reply.
Yes, I am using a volume resistance. At the porous region, a momentum source term will be added, representing the pressure gradient. In the axial flow region, this term would be zero. I am wondering what it would be at the interface.
In axial flow, its value will depend on the resistance coefficients you have used in all three directions. I don't understand why you say it will be zero. Can you post some snaps to elucidate your geometry/BCs so we can understand where the interface is exactly?