2D and 3D meshing

Sham

Hi,

I am modelling a flow past cylinder with a circular domain of 20xDiameter in radial. I have modelled a 2D cylinder and the mesh around the cylinder is very fine.

My question is, if I want to move to 3D, should I keep the mesh density as in the 2D case or can I corasen the mesh. I found that if I were to keep the same mesh density and extrude to 3D, the number of cells will be out of limit for Fluent 6.3 to read.

Can I coarsen the meah? Will I obtain same accuracy?

Sham.