boundary conditions for 2D flow around a circle
 

Can anyone tell me (or point me to a reference) about the boundary conditions for 2D flow around a circle. I think I use a velocity inlet on the left, outlet on the right, and free stream on the top and bottom? My problem I think is how to specify the free stream boundary conditions for velocity and pressure (using the SIMPLER method).

For the circle I use wall boundary conditions, zero gradient pressure and wall functions for velocity.
For the inlet I am setting the velocity and allowing the pressure to be solved.
For the outlet I am setting the pressure to zero and apply a zero gradient to the velocity. Is this correct?

My reason for this is in trying to solve stability issues, where my code becomes unstable after a Re number of about 500. Any help is appreciated, thank you in advance.