How to setup Interface surface

Michi_21453

I made common surface in between two adjacent bodies by executing geometry validation. I want to setup this surface as a interface surface (Surface with No simple boundary condition) but I couldn't find any command icon in ribbon menu. Could you please tell me how to setup interface surface. 

acupro

Any surface left in the Default/Auto wall set will be handled by the AutoWall functionality.  By default, if there is fluid on both sides of that surface, it will not have any Simple BC applied to it, so will be treated as a flow-through surface automatically.  Similarly, if there is fluid only on one side of a surface left in the Default set, it will be treated as a wall.