I have read several papers on CFD. I want to know how the 'O' grids are defined ? eg. what do we mean by 192*256 'O' grid size . As we can see in the image attached.
The supplied example O-grid is a rectangular grid about 40 wide x 128 long, wrapped around and joined. It is so-called because it resembles the letter "O".
For more details see http://www.innovative-cfd.com/cfd-grid.html