outflow BC in SIMPLE
 

I am doing a simulation on laminar Karman vortex shedding over a circular cylinder to test my code.

It is for incompressible flow, using SIMPLE algorithm on unstructured mesh.

Does anybody know the boundary condition for this case (esp. the outflow)?

On the outflow, should I set pressure correction to zero or zero gradient and what about velocity? Assuming this boundary is far enough from the cylinder.

I found a paper saying that for incompressible flow, all BC's for the pressure correction equation should be Neuman, is that true?

If on the outflow, we set a Neuman BC for pressure correction, then the velocity must be fixed, is that true? If that is true, how to set this BC for velocity?

Thanks.