Interior zones exported as walls in GAMBIT
Sometimes, geometries have some hanging faces (i.e. faces with some edges which are not part of atleast 2 other faces). GAMBIT, by default
treats such faces (and also hanging edged if any) as boundary zones, and therefore assigns "Wall" boundary condition to them instead of "Interior" boundary
condition. This could create problems in Fluent and can give erroneous results if not noticed in Fluent.
To avoid such problem from occuring, following can be done in Gambit:
1. Go to Edit -> Defaults in Gambit.
2. Click on FILE_IO and turn ON MESH.
3. Change the value of variable UNSPECIFIED_BOUNDARY_ENTITY to interior and click on Modify.
4. Gambit will create one interior zone with the name "wall" which will have the hanging face and also other unspecified faces on
the boundary of the volumes in the geometry.
5. Now export the mesh and read it in Fluent.
6. While reading Fluent will first separate the interior zone "wall" into 2 parts (because the hangin face and the boundary faces
are not connected). Then it will change the Boundary condition type of the separated boundary faces of the
volume to "Wall" as these faces have only one adjacent cell threads.