Domain interfaces are always required when multiple assemblies are used within a domain or across multiple domains. If you do not create the required domain interfaces, the regions will remain part of the default wall boundary condition.

Domain interfaces are also always required when multiple domains are created within a single assembly. If you do not create the required domain interfaces, default domain interfaces will be created which may or may not be appropriate.

Domain interfaces are not required when multiple 3D regions within the same assembly are selected for a single domain.

Any given domain must contain at least one node that is not used in a domain interface. Domains defined only by interface nodes will not be accepted by the CFX-Solver.

You cannot use Mesh Adaption when a simulation contains domain interfaces.