I wan to know that whether icem applies boundary conditions to cell centers or vertexes?

BCs would be written appropriately for the selected solver. The solver would then read the mesh and BC files and do the correct implementation.

Not sure exactly your meaning about "applies BC to cell centers/ vertices".

As myron said, it depends on your flow solver code. You probably need to define boundary condition in ICEM, if you are using StarCD. I don't remember that I have to do that for CFX.

John, I believe CFX is using vertices, since if you set a monitor point in CFX the result relates to the vertex next to your defined coordinate. ICEM provides only the finite volumes, but CFX subsequently refers to the vertices. This is what the others tried to say before. Hope this helps. TobiasZ