Porous media - air zone interface

[HilaryE]

Dear All,

I prepare a model for 2D airflow analysis in Fluent.
Air flows through inlet -> air zone -> porous media -> air zone -> outlet

I am not sure whether I should define somehow the interface between porous media and 'air zone'.

Also I have another question related to selection of walls in my analysis. Please see the drawing attached.

I would be grateful for your help.
Thank you.
Regards