what is "C grid" "O grid"

Hi ztdep,

C-grid and O-grid are types of structured (mapped) hex/quad grids.

As an example, consider a structured quad grid for an airfoil. In an O-grid, one family of grid lines goes around the airfoil, from the airfoil surface to the outer boundary. The other family of grid lines go radially from the airfoil to the outer boundary. Because the first family of lines go around the airfoil they are "circular" shaped like the letter "O" - hence the name.

Here is a picture of an O-grid.

http://www.innovative-cfd.com/images/O-grid-small.jpg

For a C-grid, consider the airfoil again but imagine that a grid line exists for the wake. So the first family of grid lines starts at the downstream boundary, goes forward around the front of the airfoil, and then back out the downstream boundary. That gives them the shape of the letter "C" (if you use your imagination).

Here is a picture of a C-grid.

http://upload.wikimedia.org/wikibook...ca0015grid.png

There's also an H-grid, but I think you can probably figure out what that topology looks like.

Hope this helps.

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