## Chapter 17: Subdomains

A subdomain is a 3D region within a predefined domain that can be used to specify values for volumetric sources. Fluid or porous subdomains (that is, when the parent domain is of type Fluid) allow sources of energy, mass, momentum, radiation, Additional Variables, components, and turbulence to be specified. Solid subdomains allow only sources of energy and radiation to be set.

This chapter describes:

- Creating New Subdomains

- The Subdomains Tab

- Basic Settings Tab

- Sources Tab

- Fluids Tab

- Mesh Motion

A domain must be created before a subdomain can be created. The location of a subdomain must be a 3D region that is part of a single parent domain. 3D primitives are implicitly included in a parent domain if 3D composites or assemblies are used in the domain location. A subdomain cannot span more than one domain, but you can create many subdomains in each domain. You should consider subdomain requirements when you generate a mesh, because subdomains must be created on existing 3D regions. Definitions for primitive and composite regions are available in Mesh Topology in CFX-Pre.

Additional information on the physical interpretation of subdomain sources and modeling advice is available, as well as additional information on the mathematical implementation of sources, is available in Sources in the CFX-Solver Modeling Guide.

The CFX Expression Language (CEL) can be used to define sources by creating functions of any CFX System Variables. For details, see CEL Operators, Constants, and Expressions in the CFX Reference Guide.

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