2-D grid around airfoil in Gambit
 

I want to make 2-D grid around airfoil in Gambit, but I don't know which types a the better - C-grid, O-grid, H-grid or other or hybrid.
Also I don't know what must be the farfield size.

Can anyone help me?

Thanks..

C grid wud be good for structured mesh
farfiled size- 15c for subsonic flow

Why the farfiled size is 15c...
Where can I read about it.

read the pre-farfiled BC from help files, it recomends 20c for external flows,
for subsonic flow (mycase) 15c isl wrking....