## 5.1. Overview of Domain Interfaces

Before reading this section, you should be familiar with the concepts of primitive regions, composite regions, and assemblies in CFX-Pre. For details, see Mesh Topology in CFX-Pre in the CFX-Pre User's Guide.

Domain Interfaces provide a way of connecting meshes or domains together. There are many uses of them. For example, they can be used in the following situations:

- If the flow field is repeated in multiple identical regions, then only one region must be solved, but the boundaries are specified as periodic (via a rotation or translation). A pressure change or mass flow rate may also be imposed for a translationally periodic interface.

- Domains can be connected together with a domain interface. This is often useful for connecting static domains together with non-matching grids. For example, hex meshes can be connected to tetrahedral or hybrid meshes. This is a useful strategy for reducing meshing effort. Pitch change can also be included.

- You can use domain interfaces to reduce mesh generation effort. The “divide and conquer” principle is useful, where the daunting task of generating a single mesh for the entire domain is divided into the much simpler task of generating a series of meshes that are later connected together.

- Domains that have a change in the reference frame (such as rotor-stator) can be connected together. Pitch change can also be included.

- Domains with different physical types can be connected together. For example, energy may flow through a fluid-solid interface. These interface types are often generated automatically. Other examples are fluid-porous and solid-porous interfaces.

- A domain may contain multiple mesh blocks. Non-matching interfaces can be connected together using a domain interface.

- A domain interface can be defined as a thin surface; a thin surface that has its Mass and Momentum set to `Conservative Interface Flux` can have physics defined across it.

Two methods of connecting meshes exist in ANSYS CFX; these are one-to-one (direct) and general grid interface (GGI). Additional information on these connections and when they are used is available in Mesh Connection Options.

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