FLUENT V6 - how to find the ID number of the interior face zone that is generated by the interface boundary type
Sometimes, one needs to calcuate the mass flow rate through the interior face zone that is generated by the interface boundary type between two meshed volumes. This is typically done within a UDF. The ID number of the interior face is needed to calculate the mass flow rate through it. The id for a face zone is normally obtained from the boundary condition panel. However, in this case, that id is not provided in the boundary condition panel since this interior face zone name is not accessible to the user. This solution provides an alternative approach to determine that ID.
The above command will show something like this:
((if (sb1-id . 3) (sb2-id . 10) (interior-id . 7) (periodic-id . 0) (bnd1-id . 13) (bnd2-id . 14) (periodic . #f) (coupled . #f) (face-periodic . #f) (mperiodic-ids)))
which shows in this example that the interior zone that is created has a thread id of 7.
The above command also works in FLUENT V6.3 with "many to many" interface. Instead of one interior face zone, one obtains multiple interior face zones in this case.