CGNS CFD Data Standard

by John Steinbrenner / Pointwise
on behalf of
CGNS Steering Committee

What is CGNS?

• CFD General Notation System
• A standard for recording & recovering CFD data.
  • Facilitates data exchange between sites, software, and computers
  • Stabilizes archiving of data
• Free, open source: www.CGNS.org

CGNS History

• 1994: Boeing & NASA identify file transfer as the main impediment to CFD technology transfer.
• 1995-98: CGNS developed under NASA contract NAS1-20267 (AST Program)
• 1998: 1st Release
• 1999: CGNS Steering Committee formed (subcommittee of AIAA Comm. on Standards)
• Specific Goal: CGNS output from pre-processors

CGNS Technology

• Intellectual content
  • SIDS (Standard Interface Data Structures)
    • Rules for organizing CFD data
  • File mapping
• Implementation
  • Mid-Level Library
    • API that understands SIDS and file mapping
    • cg_*
  • ADF (Advanced Data Format)
    • Portable binary I/O
    • Tree data structure
    • adf_*

CGNS Philosophy

• Target 3D, multi-zone, Navier-Stokes solutions (and subsets thereof)
• Assume CFD data consists of small number of large arrays
• Employ a topology based, hierarchical, treelike structure

SIDS Content

• Grid coordinates, elements, & flow solution
  • Structured or Unstructured
• Multi-zone connectivity
• Boundary conditions
• Governing flow equations
• Time dependency
• Miscellaneous (reference states, convergence history, etc.)
• Extensions for new technologies and capabilities
  • Input from CGNS community at large
  • Documented in SIDS
  • Implemented in API

CGNS Standardization

• AIAA Recommended Practice R-101-2002
  • Review/voting complete 01 June
• Implementations
  • Various commercial software vendors, end user organizations, etc.
• ISO STEP Standardization

ISO STEP

• STEP - STandard for the Exchange of Product model data - ISO 10303
• Goal - CGNS to be ISO standard for Fluid Dynamics data
• AP237 - Fluid Dynamics
• Strategy
  • AP for CFD data
    • Based on existing CGNS
  • Extend to other fluids data
    • Wind tunnel, flight test, hydrodynamics

ISO STEP Requirements

• Strong link to product data management
  • Record of all data sources, persistent links
• Re-Use existing data structures to full extent
  • AP203 - geometry
  • AP209 - finite element analysis
  • AP232 - technical data exchange
• ASCII only
  • Need binary

CGNS - ISO Timeline

• 3 page-by-page reviews at ISO SC4 meetings within last 12 months
• June 2002 - release mods to Committee Draft Ballot
• Fall 2002 - workshop for interested parties in Fort Worth, TX (Lockheed host)
• Nov 2002 - ISO SC4 meeting in Seoul
  • Hope to release AP237 to committee draft ballot (aggressive)

ISO STEP Approval Process

• Requires number of favorable votes at each "gate"
• More votes required with each successive "gate"
• Approximately 17 P-member countries - one vote per country
• CGNS users currently exist in each P-member country
• Final ballot in 2004-2005

Use It!

• Add CGNS to your applications
  • Download docs, source, binaries from CGNS.org
• Get involved at CGNS.org
  • Participate in telecons
  • Subscribe to CGNSTalk
  • Promote CGNS
  • Propose & work on extensions