## Chapter 13: Domain Interfaces

Domain interfaces have multiple purposes:

- Connecting domains or assemblies

  Domain interfaces are required to connect multiple unmatched meshes within a domain (for example, when there is a hexahedral mesh volume and a tetrahedral mesh volume within a single domain) and to connect separate domains.

- Modeling changes in reference frame between domains

  This occurs when you have a stationary and a rotating domain or domains rotating at different rates.

- Creating periodic interfaces between regions

  This occurs when you are reducing the size of the computational domain by assuming periodicity in the simulation.

- Creating thin surfaces

  Thin surfaces enable you to model physics such as heat transfer across a thin material or gap without needing to explicitly mesh the surface. For example, thin surfaces can be used to model contact resistance at a solid-solid interface, a thin film on a fluid-solid interface, or a thin baffle at a fluid-fluid interface.

Interface boundaries are created automatically for each domain interface. For details, see Interface Boundary Conditions.

Additional information about domain interfaces is provided in Overview of Domain Interfaces in the CFX-Solver Modeling Guide.

Note: If you are running a simulation with ANSYS Multi-field coupling to the ANSYS solver, you will need to create fluid-solid interfaces with the fluid side in CFX and the solid side in ANSYS. Such an interface is actually an external boundary so far as CFX-Solver is concerned, as it lies on the boundary of the CFX domain(s). You should create a Boundary Condition, not a Domain Interface, when setting up such an interface.

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