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CGNSBASE - Use CGNS files
This keyword specifies that the grid and flow data are obtained from,
and written to, CGNS (CFD General Notation System) files, not
The user-specified basename is the name of the CGNSBase_t
node in the grid and flow files.
[Detailed information on the CGNS standard may be found at the
CGNS web site
It should be noted that, strictly speaking, there is no notion of a
CGNS file, only of a CGNS database implemented within one
or more ADF (Advanced Data Format) files.
We nevertheless use the terminology "CGNS file" in the Wind-US documentation.
In addition, a true CGNS database has a single CGNSBase_t node
as its root.
In the current Wind-US implementation, however, the grid and flow solution
are stored in separate files, with both files having their own
CGNSBase_t node with the same basename.
When CGNS files are used, the extensions for the grid and flow files must
be .cgd and .cfl, respectively, the same as when common
files are used.
If the CGNSBASE keyword is used, the files are read as CGNS files.
If the CGNSBASE keyword is not used, they are assumed to be common
Wind-US supports the most common CGNS features, but not all.
Some specific limitations on the implementation of CGNS in Wind-US
are listed below.
- Many Wind-US input options may be specified on a zonal basis, using
the zone number to identify the zone.
In the CGNS standard, zones are identified by a name.
When CGNS files are used in Wind-US, it is assumed that the zone
number maps to the zone's position in an alphanumerically
sorted list of zone names.
Note that the naming convention Zonen, where
n is the zone number, is alphanumeric only up to Zone9.
Zone10 through Zone19 would get sorted between
Zone1 and Zone2, and so on.
However, spaces are allowed in names, so
"Zone n", with two spaces, (e.g.,
Zone 1, Zone 2, ...,
Zone 99, Zone100, ...) is alphanumeric up to
- The CGNS default names "GridCoordinates" and
"FlowSolution" are used for the CGNS GridCoordinates_t
and FlowSolution_t nodes.
For each zone, only one grid and one flow solution are stored.
- In a CGNS database, the scaling data must be stored with the data
itself, but the units to be used may be stored with the data or
higher in the node tree.
The Wind-US implementation assumes that the units are stored with the data.
- If grid velocities are stored in the grid file, it is assumed that
the units are ft/sec.
- The CGNS nodes for storing time-dependent data are not yet supported
- For overlapping grids, CGNS allows hole points to be identified
using multiple OversetHoles_t nodes.
Wind-US currently assumes that all hole points in a zone are identified
in a single OversetHoles_t node, using a PointList.
- Wind-US writes convergence and time history information to the
list output (.lis) and time history (.cth) files,
respectively, not to a CGNS file.
There are also some Wind-US features and capabilities that are not
supported by the current CGNS standard.
These include chemistry and
MFD flows, specified boundary
layer transition, and bleed boundary conditions.
Several proposals are pending to extend the CGNS standard, but for
now CGNS files created by Wind-US for these types of flows may not be
fully CGNS compliant, and should be considered unique to the Wind-US