CGNS
Interface
|
Data
Format |
CGNS
Version 3.0 (ADF / HDF) |
|
Type
of mesh |
unstructured
or structured mesh |
|
Dimension |
2D
and 3D |
The ANSYS ICEM CFD - CGNS output interface creates a CGNS file in accordance with the SIDS. It uses the CGNS mid-level-library endorsed by the CGNS Steering Committee to create the file. This interface supports both structured and unstructured mesh translation.
Creating the CGNS
file
The
CGNS output interface can be invoked from the AI*Env main window.
Under the menu "Output", "Select solver",
select "CGNS". Then select "CGNS Input".
A window opens to allow the specification of the files to be translated into
the CGNS format. An existing unstructured mesh file or a set of
structured mesh files must first be selected. In addition, the
output interface requires the boundary conditions file, and for structured mesh
input, the topology file. It offers options to define the name of the
CGNS file and to select the automatic creation of boundary condition
patches. For unstructured mesh input, the user has the additional option
to select whether the boundary condition patches are defined using nodes or
face elements. Default names for the ANSYS ICEM CFD input files and the
CGNS file are given. These can be modified as necessary.
The interface generates the CGNS file in the current project directory.
Connectivity
This
translator supports 1-to-1 connectivity only.
Defining boundary
conditions for CGNS (optional)
After
generating the mesh, and prior to running the translator, boundary conditions
for CGNS can be defined using the CGNS
Graphical User Interface. Under the menu "Output",
"Select solver", select "CGNS".
Then click on the "Boundary conditions" icon. The "Family
Boundary Conditions" window opens allowing to set boundary conditions on
the mesh families. Two boundary conditions types are available; BCType
and BCDataSet. Note however that BCDataSet in a subset of BCType in CGNS
and therefore can not be defined by itself. A boundary condition patch
can either have a BCType alone, or a BCType with one or more BCDataSets.
BCType
The boundary condition types (BCType) are defined in the SIDS. They identify the equations that should be enforced at a given boundary. To define a boundary condition type, select a boundary family (face in 3D, edge in 2D) and one of the BCType in the provided list.
BCDataSet
Boundary condition data sets are used to define the BCTypeSimple, and one or more global boundary condition data. When boundary condition data are specified, the boundary condition type must be selected. It can be either "Dirichlet" or "Neumann". Only uniform boundary condition data are supported by the translator; the data given are applied to the entire boundary condition patch. The list of variables corresponds to the standardized "Data-Name Identifiers" found in Annex A of the SIDS.
In general, BCTypeSimple is the same as BCType and no more than one
BCDataSet is required. In some particular cases however, the boundary condition
type can be flow dependent. In such case, BCTypeSimple differs from BCType. The
SIDS defines these special cases as "compound boundary conditions".
For example, an inflow boundary where the flow goes from subsonic to supersonic
would require a compound boundary condition. In such case, two BCDataSets would
be added, each with a different BCTypeSimple:
(1) with BCTypeSimple = BCInflowSubsonic
(2) with BCTypeSimple = BCInflowSupersonic
For more details on the use of compound boundary conditions, please refer to
the SIDS.
3D elements groups for unstructured grids
The CGNS standard does not provide a specific method for grouping elements. Our translator offers this feature by creating a "DataArray_t" node under "Zone_t/DiscreteData_t". This "DataArray_t" node is named "PID" and contains on array of integers for the pid of each element. Each element's PID is set to its family ID number. The order in which the element's PIDs are listed follows the same order as the global element numbering under "Element_t".