Porous media model - empty surface and interior generation at interfaces?
 

I apologize if this question has been asked before, but I wasn't able to find a solution from a preliminary scan of similar threads. I've noticed that in my model, there seems to be an excessive generation of empty surfaces and interior zones every time I create an interface. I've been able to get reasonable results so far, but I want to be sure that I'm doing this correctly.

The geometry I'm modeling is like a rectangular cross-section mixing tee with three "mixing inlets" instead of one (see image attached). I've split the body into five distinct zones so that the three inlets, each their own separate body, feed into a porous zone, which is connected on the other side to the primary fluid body. The porous zone is treated as a laminar, porous cell zone and the other four bodies (3 mixing inlets and primary fluid body) are grouped together as a single fluid cell zone. Even when I group all walls together in the meshing utility as one named section, "wall", every time I import the mesh into Fluent it creates many more named sections than I specified, with 4 extra interior zones and 8 extra wall zones that I can't view even if I try (I get the error: "Note: zone-surface: cannot create surface from sliding interface zone.
Creating empty surface."). What are these zones supposed to represent? Can I get rid of them by doing something different with my meshing/geometry setup?

If it helps, I used the Fluid Flow (Fluent) meshing utility.

For anyone with this problem in the future - I've figured out the issue since I made my post.

Anytime you have a sliding interface, Fluent creates two types of extra "shadow" zones for boundary condition definition purposes: shadow "wall" zones are created where two sides of an interface do NOT overlap, and a sort-of shadow "interior" zone is created where two sides of an interface DO overlap. This is so Fluent can keep track of (and update) the regions of the interface that fluid can pass through (the interior zones) and the regions of the interface that fluid cannot pass through (the wall zones).

You can check this using the problem I already posted - 4 extra interior zones were created because there are 4 regions of interface overlap (3 on the bottom and 1 on the top) and 8 extra wall zones, 2 per interior zone (one for wall cells to the left of the interior zone and another for wall cells to the right of the interior zone). In certain cases, some of these boundaries zones (like shadow walls) may not contain cells at the start of the problem, but if the sliding interface moves such that a wall will be produced to the left or right of the interior zone, Fluent has a boundary zone ready to accept those cells.

Interface defining problem in Fluent
 

I am facing the problem while defining the interface. My problem is a 2D case containing 2 fluid zones and the porous zone in sandwiched between the two fluid zones. If I am not defining the interface in the mesh then in the fluent it is automatically taking the interfaces as wall and no velocity diffusion can be seen in the porous zone. If I am defining the interface in the mesh then also connecting the interface in the fluid create walls on the interface. So,no velocity diffusion can be seen in the porous zone.

Please help me in this regard. I will be very thankful to you. It's urgent please.