Interface boundary is used, when the surface is shared by both Fluid and solid regions. If you can explain the problem in detail, may be i can describe it in more detail.

Interfaces, in the sense of Fluent, are matching surfaces with different mesh topology.

Dear Sedek,

In the Design Modeler, Click on both the faces and make them as a single part. In this case the interface will be shared by both the faces.

Hope this helps.

How does Fluent interpolates data between cells in vicinity of each other at interface boundary??? ( In this case, the interface is defined between the two fluid zones, and the cells' nodes of the two zones are not coincident with each other)

I am faced with a lot of contact regions in the mesh component which are generated automatically. Also, these contact regions are considerable as interface boundary condition on the Fluent. I am wondering to know:

first, should I try to eliminate contact region in the mesh part or not?  

and then, what is the meaning of interface bc in Fluent? is it like interior? 

Thank you in advance due to your responds.

Hi guys. I have a problem with fluent and I need some help.

As can be seen in attached photo, I have two box which are attached to each other. Cold water and hot water flows through upper and lower box respectively. The body of box is from aluminum. left and right side of both boxes are symmetry.

Because in real geometry I have several of these boxes on top and down (hot,cold,hot,cold,...) I need to use periodic boundary condition for top and bottom surfaces. As I found I should define them interface in gambit and then in fluent from "mesh interface", select "coupled". So top and bottom surfaces should be attached to each other and have same temperature profile. But it didn't work and I don't know why?!!!

Could you please help me? I just need to connect the top and bottom faces thermally (we don't have any fluid flow there).

Thank you guys.

Dear Sankar Ram T,

I think mass transfer can also take place through interface. Refer the following link.

https://youtu.be/HqaL9Bw8gQs?t=1m44s