Coordinate Systems

Coordinate systems are used to specify spatial vectors, such as position and direction for boundary and region values, initial conditions, and properties of location and direction for derived parts. Coordinate systems are also used to define the position of sketch planes in 3D-CAD. For simple applications, the default laboratory coordinate system is sufficient. However, more complex situations can benefit from the definition and use of a local coordinate system or a block-mapped coordinate system.

In Simcenter STAR-CCM+, any coordinate system is represented by a node under Tools > Coordinate Systems.

Laboratory Coordinate System

The laboratory coordinate system is the base system in which all other local coordinate systems are defined. The laboratory coordinate system is a Cartesian system. It exists in every Simcenter STAR-CCM+ simulation by default, and cannot be deleted.

The laboratory coordinate system is represented by the Laboratory node. This node contains a child node, Local Coordinate Systems, that is used to manage all local coordinate systems (and their derived systems) within the simulation.

Local Coordinate System

A local coordinate system can be defined in terms of Cartesian, cylindrical, or spherical coordinates and can take either the base laboratory coordinate system, or a previously defined Cartesian local coordinate system, as the reference system. A local coordinate system can also be exported from a sketch plane in 3D-CAD for use in Simcenter STAR-CCM+.

In the simulation tree, the reference system acts as a parent node. Several layers of nesting are permissible, up to the memory limit of the computer. The Local Coordinate Systems manager node manages local coordinate systems and is a child node of the relevant reference coordinate system.

Local coordinate systems can be accessed by derived parts and reports, and also serve as scalar and vector field functions. Examples of how they can be used are:

  • Initializing the velocity in a region to solid body rotation
  • Providing a swirling inlet velocity profile

For more information on Cartesian, cylindrical, and spherical coordinate systems, see the Theory Guide section Coordinate Systems. When defining coordinate system parameters, you can specify an expression that references other quantities within the simulation, including global parameters. If you are working in conjunction with a CAD Client, then the expressions can also reference CAD parameters and CAD responses (only in Simcenter STAR-CCM+ Client for NX).

Block-Mapped Coordinate System

A block-mapped coordinate system is a type of user-defined coordinate system in Simcenter STAR-CCM+, that defines points based on evenly distributed gradations between selected end surfaces in a topological cube. Each coordinate direction has a range of 0 to 1, where [0, 0, 0] defines one corner of the cube, and [1, 1, 1] defines the diagonally opposite corner of the cube.

This type of coordinate system makes it possible to create iso surfaces that follow the contours of the bounding surfaces, as would be desired, for example, in turbomachinery post-processing for generating blade-to-blade or meridional views.

The system is represented in the simulation tree by a node that has its own properties and is subject to common menu items. This coordinate system permits the creation of section surfaces along periodic directions, and has its own field functions.

The six subnodes in the Block-mapped node, known as block-mapped boundaries, represent the six sides of the topological cube. Each side should consist of one or more boundaries that you select when creating this coordinate system. All boundary edges in the group should be connected to one other boundary to form a closed cube.