CFD-General Notation System
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| CFD-General Notation System | |
|---|---|
| Name | CFD-General Notation System |
| Acronym | CGNS |
| Developer | National Aeronautics and Space Administration, European Space Agency, Japan Aerospace Exploration Agency |
| First release | 1990s |
| Latest release | ongoing |
| Genre | data standard, file format, metadata |
| Website | NASA, ESA, JAXA collaborations |
CFD-General Notation System is a standardized data model and file format developed to store, exchange, and archive computational fluid dynamics datasets and associated metadata. It provides a common schema that enables interoperability among simulation codes, pre/post-processing tools, visualization packages, and archival repositories maintained by organizations such as National Aeronautics and Space Administration, European Space Agency, Japan Aerospace Exploration Agency, United States Department of Defense, and industrial partners like Boeing, Airbus, and Lockheed Martin. The system emphasizes portability, self-describing structure, and support for complex grid topologies and multi-physics datasets used in collaborations among institutions including Massachusetts Institute of Technology, Stanford University, Imperial College London, and German Aerospace Center.
Overview
The notation system originated from collaborative initiatives led by National Aeronautics and Space Administration and later adopted in coordinated projects with European Space Agency and Japan Aerospace Exploration Agency, responding to challenges faced by researchers at NASA Langley Research Center, NASA Ames Research Center, Sandia National Laboratories, and aerospace companies such as Rolls-Royce plc and General Electric. It defines a hierarchical data model with explicit support for structured, unstructured, overset, and hybrid grids encountered in legacy solvers like those from ANSYS, Siemens PLM Software, and in-house codes at Los Alamos National Laboratory and Argonne National Laboratory. The model accommodates boundary and initial conditions used in projects funded by National Science Foundation and multinational funding bodies such as European Commission. Adoption has been promoted through workshops at venues including International Conference on Computational Science, AIAA Aviation Forum, and ICFD meetings.
Notation Principles and Symbols
The system's notation emphasizes clear naming conventions and symbol sets drawn from conventions used in seminal texts and standards referenced by American Institute of Aeronautics and Astronautics and International Organization for Standardization. Core entities are named for meshes, zones, solution arrays, and discrete functions; these echo variables familiar to researchers at Caltech, Princeton University, University of Cambridge, and ETH Zurich. Metadata fields record provenance information aligned with archival practices at National Archives and Records Administration and data repositories like Dryad and Zenodo. Symbols for coordinates, connectivity, and topology are expressed through tags comparable to those used in file formats developed by NetCDF and HDF Group, and adopt vocabulary similar to standards from ISO/TC 211 spatial data committees. The notation supports labeling of boundary patches and solver-specific flags used by codes such as OpenFOAM, SU2, and proprietary packages from Dassault Systèmes.
Applications in Computational Fluid Dynamics
Practitioners apply the notation to exchange aerodynamic datasets between institutions like NASA Glenn Research Center and industrial partners including Safran and Pratt & Whitney, to archive turbulence-resolving simulations performed on supercomputers at Oak Ridge National Laboratory, National Energy Research Scientific Computing Center, and EuroHPC centers. The format has been used for multi-fidelity studies bridging experiments at CERN (wind tunnel analogues), wind engineering cases involving Imperial College London, automotive aerodynamics with Volkswagen, and environmental flow modeling in collaborations with United Nations Environment Programme. It supports unsteady, steady, compressible, and incompressible simulations, enabling coupling with structural solvers in multidisciplinary analyses performed at NASA Langley Research Center and CEA Saclay.
Implementation and Software Support
A reference implementation and libraries have been developed and maintained by consortia including teams from NASA, University of Michigan, and University of Illinois Urbana-Champaign, with bindings for languages used in research and industry: Fortran, C, C++, Python, and MATLAB. Major visualization and processing tools such as ParaView, VisIt, Tecplot, and proprietary suites from Siemens support the format either natively or via plugins. Integration efforts have been demonstrated with meshing tools like Gmsh, converters for CGNS to VTK or HDF5-backed archives, and workflow managers used at Lawrence Livermore National Laboratory and Pacific Northwest National Laboratory. Certification and compliance testing are periodically organized at conferences hosted by AIAA and software summits at Supercomputing Conference.
Examples and Case Studies
Representative case studies include transonic wing computations exchanged between NASA Langley Research Center and Boeing for validation of Reynolds-averaged Navier–Stokes solvers, large-eddy simulations archived by Oak Ridge National Laboratory for turbulence studies, rotorcraft aerodynamics datasets shared with Bell Textron, and urban microclimate simulations involving University College London and Met Office. Benchmark collections used in academic competitions at ICCS and datasets linked to publications in Journal of Computational Physics and AIAA Journal illustrate portability across solvers such as OpenFOAM and SU2 and post-processors like ParaView.
Extensions and Related Notation Systems
Extensions address multi-physics coupling, high-order discretizations, and mesh motion; these have been developed in collaboration with research groups at Caltech, ETH Zurich, and University of Toronto. Related standards and formats that intersect include those from HDF Group, NetCDF, and domain-specific conventions in projects led by European Organisation for the Exploitation of Meteorological Satellites and International Association for the Engineering Modelling, Analysis and Simulation Community (NAFEMS). Interoperability efforts continue with initiatives at Open Geospatial Consortium and data curation programs by Digital Science and institutional repositories at MIT Libraries.