In places where you are required to select a 2D Region to specify a location for a meshing feature, CFX-Mesh recognizes two types of 2D Region: Primitive and Composite. The primitive regions are those which exist in the geometry by default: there is one for every external face and two for each shared face (see 2D Regions and Faces for more details). You can select these 2D Regions directly from the geometry in the Graphics window. The composite regions are those which you create explicitly, and consist of one or more primitive 2D Regions which you select and give a name to.

You can create a Composite 2D Region from any single primitive 2D Region or group of primitive 2D Regions. No primitive 2D Region can be assigned to more than one Composite 2D Region. A Default 2D Region is created by CFX-Mesh and cannot be renamed or deleted; this always contains any primitive 2D Regions that have not been used in other Composite 2D Regions, and its contents change dynamically as you create and modify other Composite 2D Regions. In this way, every primitive 2D Region is always assigned to exactly one Composite 2D Region. If the Default 2D Region should become empty then it is automatically removed, but will re-appear if any Composite 2D Region ceases to be used by the other user-defined Composite 2D Regions.

To create a Composite 2D Region, right-click over Regions in the Tree View, and select Insert > Composite 2D Region. You can then select the required primitive 2D Regions from the Graphics window. A Composite 2D Region can be deleted or renamed by right-clicking over its name in the Tree View.

You can use the Composite 2D Regions to specify locations for meshing features in CFX-Mesh, rather than having to select the faces individually. Simply click on the name of the Composite 2D Region from the Tree View to select it, instead of clicking on the faces in the Graphics window.

Any Composite 2D Regions that you create in CFX-Mesh appear in ANSYS CFX-Pre and can be used as locations for boundary conditions and domain interfaces. The 2D Regions and their names are written to the CFX Mesh file with the mesh. Even if you do not specify any Composite 2D Regions in CFX-Mesh, mesh on the primitive 2D Regions will still be available for selection to define boundary conditions in ANSYS CFX-Pre. However, the following advantages apply if you create at least some Composite 2D Regions in CFX-Mesh:

You may also want to create additional Composite 2D Regions if, for example, you want to create plots on individual or groups of faces during post-processing.