Hi, I'd like to know how to define,if it is possible , a periodic surface in Gambit. Is this a condition that I can define in Fluent or in Gambit?

After you do all of your work on the geometry (splitting, merging, etc...) link each pair of faces that are going to form your periodic boundary condition. This is done in the surface mesh window... looks like the link of a chain. Make sure to turn on the periodic option before linking the faces. Once you have all of your faces linked properly, then you can mesh your model. Then in the surface BC window, select all of the faces that form your periodic boundary condition (don't create one BC for each side... put all of the faces into a single BC). Then define the rest of your BCs and export the mesh.

If it's a rotational periodic BC, then check to make sure that the rotational axis for the fluid is the same as the rotational axis of the BC (Define->Boundary Conditions->Fluid... Check the Rotation-Axis Origin and Direction). You should be all set.

Hope this helps, and good luck, Jason

Correct me if I'm wrong, but I believe you can also specify a perdiodic surface in Fluent:

-after you mesh your object, specify each face that you want to make a periodic face individually using some BC...say a wall for example

-load into fluent and then type "grid", and then "modify-zones", and then "make-periodic". Type in the names of the two faces that oppose each other that you want to make periodic. Fluent will do the linking.

The benefit I see from this is that it seems like it would be easier if you decide to change your BCs in Fluent at some later point, rather than having to go back into Gambit and modify your geometry there.