COMSOL doing periodic boundary conditions in navier stokes

jwq

Please can anyone tell me how to set this up?

I know how to do the required settings in the Physics/Period Conditions.

However, to fully implement it, i'm also required to choose boundary conditions in the 2D incompressible navier stokes solver (e.g. wall, inlet, outflow, open boundary, stress etc). Which one shall i choose?

(According to Zimmerman's comsol textbook, it should be "Ouflow/pressure". However he's using comsol 3.2. I'm using 3.5, and this option is not available in mine. The nearest matches are "outlet/pressure" and "outlet/pressure, no viscous stress". Both of these of these require that i set a value for the pressure on each outlet boundary, which doesn't make sense to me. Setting outlet pressure values is not even mentioned in Zimmerman's book, so i assume in comsol 3.2 there's no need to in order to set up periodicity.)