You should generally create all domain interfaces that are needed in your simulation explicitly in CFX-Pre. However, CFX-Pre will create default domain interfaces in certain situations.

Domain interfaces will be automatically created, at the Write Solver File stage, when there are multiple domains within a single assembly and you have not explicitly created all the required domain interfaces. These could be Fluid Fluid, Fluid Solid or Solid Solid domain interfaces depending on the type of domain on either side of the interface.

When a default Fluid Fluid interface is created and there is no change in reference frame across the interface, the Frame Change option is set to None. When a frame change occurs, the Frozen Rotor model is used. If these models are not appropriate, you should explicitly create all domain interfaces to prevent the automatic creation of interfaces.

When a one-to-one node mapping does not exist, you must manually create the domain interfaces. If multiple domains are created using separate assemblies, domain interfaces are always required.

Fluid-solid 2D primitives are initially contained in the default domain boundary conditions. Any that remain there when a CFX-Solver input file is written are assigned to default Fluid Solid domain interfaces.

If you create a MFR case using 3D primitives from a single assembly, then a one-to-one node pairing will exist because an assembly contains a continuous mesh. However, a GGI connection is required for MFR cases. A default domain interface using the Frozen Rotor frame change model will be automatically created if no other domain interfaces are created.