Unlike a regular boundary condition that is associated with one side of a domain, a connection boundary condition is two-sided. It is applicable for interfacing domains shared by adjacent blocks and baffles (shown below). Refer to Create, Assemble special, Block, Unstructured for the definition of baffles.

CAE, Set BCs, BC Connections
Both baffle faces and interfacing domains will be listed as connections in the Set BC panel.

Tip: Overriding a block interface with a boundary condition allows the creation of a baffle at that location. Otherwise, these boundary condition regions may also be used for flow integration regions, should your solver support this capability.

Under these circumstances, the Set BC panel expands (shown below) to include a list of interfacing domains and baffles. Such domains cannot be selected unless the Select Connections checkbox is checked.

CAE, Set BCs, BC Connections
Interfacing domains and baffles are set to Connection Boundary Condition by default.

Select domains you wish to set a boundary condition on either in the list provided or in the Display window. As soon as a domain is selected, it is highlighted in white in the Display window with normal arrows indicating the side it is associated with. You may assign a boundary condition to that connection by checking the Set checkbox associated with the desired boundary condition. That boundary condition type will have its number of domains increment accordingly.

Any connections where only one side has been set will have the remaining side added to the Unspecified boundary condition. To restore a connection after one or both sides have been set to a boundary condition, you must select the sides with a boundary condition applied and set them to Unspecified. Once both sides are again Unspecified, the connection will automatically be restored.