Heat transfer through porous medium
 

Hi
Iam trying to simulate the heat transfer through porous medium.
Air enters and leaves the porous medium(porous medium-bottom wall is hot).

I have created the model in GAMBIT.I have taken a big domain, have split it in to 3 regions,named the middle region as porous , while left and right of porous are fluids.
If I specify the both the interfaces (left and right of porous medium)as wall in GAMBIT , 2 walls and corresponding wall shadows are formed in fluent. I have specified the fluid as air.Specified the porous medium parameters also.The case is not converging in FLUENT.

If I do not specify the interface in GAMBIT, the case converges.

Which method is correct?