[narendrapatel111]

I am simulating open channel flow over porous bed. water flows in porous bed as well. In Fluent, I created two zones, one for flow above the sand bed(i.e. channel) and other flow in sand bed. I assigned an interface between two zones. Sand has roughness so I need to assign roughness to interface so that top of the sand bed would be represented correctly. however, I didn't find any way to assign roughness to interface. can any one help me out? Thank you.