A CGD file is a Common Grid (CGD) file saved in the Boeing Common File Format (CFF), which is a format used by various scientific programs to store fluid mechanics-related data. It contains the x, y, z coordinates of grid points generated from captured data regarding the flow of liquids, gases, or plasmas. CGD files also store information about the grid, such as grid unit specifications, scaling data, and zone coupling information.

You will most likely only encounter a CGD grid file if you work in a scientific field that deals with fluid mechanics data, which is the study of liquids, gases, and plasmas at rest and in motion. Some examples of fields that work with CGD files include astrophysics, meteorology, geophysics, oceanography, and civil, mechanical, chemical, and biomedical engineering. CGD files may be opened by various scientific programs but they are most commonly opened with Wind-US, a scientific computation program used to solve fluid mechanics-related equations. Wind-US is developed by the NPARC Alliance, which is a partnership between the NASA Glenn Research Center (GRC) and the Arnold Engineering Development Complex (AEDC) established in 1993. The Boeing Company is also involved with the NPARC alliance and development of the program. CGD files may also be created by various scientific applications, including Wind-US. If you receive a grid file saved in the PLOT3D XYZ file format you can convert it to the CGD format using the "cfcnvt" conversion utility included with Wind-US.