The MDA CFD project version of PLOT3D has been modified to directly accept common files as input. If a flow solver uses a common file as its grid source and produces a common file as its restart file, these files most likely can be read directly into PLOT3D. This saves time and disk space by eliminating the need to produce separate files for PLOT3D. Two additional features are available in PLOT3D when reading a common file. The /ZONES= "n1-m1, ..., nl-ml" qualifier to the READ command will read only the zones n through m, where n < m. The /APPEND qualifier to the READ command will append the zones in the specified common file to the end of the zones already read in to PLOT3D. Note: In the calculation of IBLANK data for particle tracing appended grids can not be interconneted. Thus all zones to be interconnected must be in the same READ command.
To read only a grid file, the following READ command must be entered:
READ/CGD=grid_file_namegrid_file_name is the name of the common file (without the .cgd suffix) which contains the grid.
To read both a grid file and a flow file (like reading an XYZ and a Q file), issue the following READ command:
READ/CGD=grid_file_name/CFL=flow_file_namegrid_file_name is the name of the common file (without the .cgd suffix) which contains the grid. flow_file_name is the name of the common file (without the .cfl suffix) which contains the flowfield.
Some programs may produce a file in which the grid and flow field have been written to one file. To read such a file, issue the following READ command:
READ/CGF=combined_file_namecombined_file_name is the name of the common file (without the .cgf suffix) which contains the grid and flowfield information.
This example reads zones 4-9 and 12 from one file, and appends zone 3 from another file.
A standand PLOT3D Q file contains data that has been non-dimensionalized. When a user requestes a plot of "dimensional" quantities (100 (density), 110 (pressure), etc.), what is really displayed is a dimensional form using predefined conditions not related to the actual conditions. For example, the normalized pressure at infinity would be displayed as 1/γ.
When a common file flow file is processed, data will be displayed in SI units for dimensional plots (100 (density), 110 (pressure), etc.).
The normalized counterparts of the dimensional plots (101 (density), 111 (pressure), etc.) will display the data normalized by the infinity conditions. Therefore, the normalized pressure at infinity will now be displayed as 1, rather than 1/γ as in the case of using a Q file.
By using the common file, one can now see both the dimensional (albeit, SI values) or non-dimensional values of dimensional quantities.
Occasionally one may want to read only the grid out of a combined grid and flow file or may want to use only the flow field out of a combined grid and flow file and use a grid from another file. To accomplish this feat, note that PLOT3D simply assumes that the file extension defines the type of data to look for. So a file with a .cgd suffix is assumed to contain the variables x, y, and z. Thus to cause one type of file to be treated as another type of file, simply rename it before invoking PLOT3D! This works because the basic structure of all common files is the same. It is the variables within the file that determine what it is used for. PLOT3D will only read geometry when CGD= is used and will ignore any other data. In a similar manner, when CFL= is used it wants flow field data so it ignores any geometry data that may be present.
Last updated 23 June 2005