CFD General Notation System Standard Interface Data Structures

Document Version 3.2.5
CGNS Version 3.2.2, Alpha

Note the CGNS Version designation here is "3.2.2, Alpha" because quartic elements definitions have been added to Line Elements, Surface Elements, and Volume Elements in the SIDS, but this capability has not been implemented in the CGNS software yet. I.e., the official version of CGNS software is still 3.2.1, and it does not include quartic element capability. When quartic element capability is added, the software version will be upgraded to 3.2.2.

This document contains the Standard Interface Data Structures (SIDS) definitions for the CFD General Notation System (CGNS) project ; this project was originally a NASA-funded contract under the AST program, but control has now been completely transferred to a public forum known as the CGNS Steering Committee.

The purpose of this document is to scope the information that should be communicated between various CFD application codes; the target is 3-D multizone, compressible Navier-Stokes analysis. Attention in this document is not focused on I/O routines or formats but on the precise description of data that should be present in the I/O of a CFD code or in a CFD database.

This document therefore contains a precise definition of information pertinent to a CGNS database. Specifically, the following information is addressed:

• grid coordinates and elements
• flow solution data, including nondimensional parameters
• multizone interface connectivity, including abutting and overset
• boundary conditions
• flow equation descriptions
• time-dependent flow
• reference states
• dimensional units and nondimensionalization information associated with data
• convergence history
• association to geometry definition
• topologically based hierarchical structures

This SIDS document is consistent with CGNS Version 3.2. A list of major changes for earlier versions is available.

• Introduction
• Design Philosophy of Standard Interface Data Structures
• Conventions
• Building-Block Structure Definitions
• Data-Array Structure Definitions
• Hierarchical Structures (CGNSBase_t and Zone_t)
• Grid Coordinates, Elements, and Flow Solution
• Multizone Interface Connectivity
• Boundary Conditions
• Governing Flow Equations
• Time-Dependent Flow
• Miscellaneous Data Structures
• Conventions for Data-Name Identifiers
• Structured Two-Zone Flat Plate Example

The complete CGNS Standard Interface Data Structures in HTML form is also available for installation on a local system. This is a gzip'ed tar file (224K, 861K gunzip'ed), and may be downloaded by clicking on the link while holding down the shift key, assuming your browser supports this capability. A dialogue box will appear for you to specify the directory and file name. To unpack the contents, do

   gunzip -c sids.tar.gz | tar xvf -