Composite Regions that are defined in the simulation can be used as locations for domains, sub-domains, boundary conditions and domain interfaces. For example, a composite region with a combination method of Union can be used to group two separate 3D regions. A domain that spans both 3D regions can then be created using the single composite 3D region. Domain interfaces should still be created to connect the two assemblies together if the composite region does not form a continuous mesh and flow is to pass between the two assemblies. For details, see Mesh Topology in CFX-Pre.

Another application of composite regions is to set up a consistent set of locations that can be applied to a number of different simulations that use the same physics definition. By referencing the composite regions in the physics definitions, the need to edit the definitions for each mesh is avoided and if differences in the mesh topology do exist this can be coped with by editing the composite regions used to locate the physics relatively simply. In this way for every problem in which the physics is to be applied, the mesh, region CCL, and physics CCL can be imported. Locations of boundary conditions, domains and subdomains should all match provided that the composite regions can all be resolved as expected.