### 1.2.14. Coordinate Frames

#### 1.2.14.1. Global Coordinate Frame (Coord 0)

In addition to being the default coordinate frame in CFX-Pre, the CFX-Solver always computes solutions in the global Cartesian coordinate frame, `Coord 0`. This coordinate frame’s origin is located at [0 0 0] and has the Cartesian basis vectors <1 0 0>, <0 1 0> and <0 0 1>. Unless specified otherwise all material properties, boundary conditions, source terms and initial conditions are calculated in the global coordinate frame.

If you are using CEL expressions, the built-in variables `xGlobal`, `yGlobal`, and `zGlobal` can be used to refer to the three coordinate indexes of the global coordinate frame.

#### 1.2.14.2. Local Coordinate Frames

In some cases, it may be useful to specify quantities using coordinates from a coordinate frame other than the global coordinate frame `Coord 0`. This is done by creating a local coordinate frame and applying it to a particular location (such as a boundary condition, initial condition, subdomain, domain) or other object that supports local coordinate frames (for example, a monitor point). For details on creating local coordinate frames in CFX-Pre, see Coordinate Frames in the CFX-Pre User's Guide.

Note:

- A variable, CEL expression, or profile data that is used in the specification of some quantity is evaluated with coordinates treated as being local, and all other non-scalar variables treated as being global. Non-scalar CEL functions (such as `torque`, `force`) are treated as being local. The quantity that was specified by the variable or CEL expression, once evaluated, will be treated as being local, if applicable (that is, if it is a vector or tensor quantity, or component thereof).

- If a domain uses a local coordinate frame other than the global coordinate frame, locations within that domain, such as subdomains and boundary conditions, do not necessarily use the same coordinate frame, because each location has its own independent coordinate frame specification.

Local coordinate frames are particularly useful for setting quantities that are not aligned with the global coordinate system, such as:

- Cartesian velocity components for initial or boundary conditions

- Cartesian flow directions for boundary conditions

- Cartesian momentum source components

- Spatially varying scalar boundary conditions

- Spatially varying properties

  Note: Cylindrical velocity components and flow directions use either a local axial coordinate direction specification or the domain rotation axis for RFR domains, as applicable. The axis specification is made using Cartesian coordinates that are interpreted in the local coordinate frame.

A local coordinate frame can have rotational frame motion applied (see Frame Motion Settings in the CFX-Pre User's Guide). A boundary condition can use such a coordinate frame to cause the location of application of profile data (or CEL expressions) to move in accordance with the coordinate frame motion.

#### 1.2.14.3. Cartesian Coordinate Frames

Cartesian vector, vector component, and tensor quantities can be associated with any local Cartesian coordinate frame in which they are meant to be interpreted by the solver.

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