Usage "open", "outlet" and "wall slip"boundaries

[Sidemountyucatan]

Hi,

I have a basic question to the boundary conditions. There is a boundary condition "open". How does it differ in practice from an "outlet" defnition or the "wall slip" condition ?

For example if I have an open tray with four side overflow and water surface, which one would fit the best for the water surface ? The "open" condition or the "wall slip" condition ?

As I know the static pressure in the "outlet" condition is a denstiy related pressure which can set to 0. In the "Open" cindition an ambient pressure has to be set. Is it also an related pressure ? If defining the four overflows as "outlets " with static pressure 0, and using "open" for the water surface do I have to define the ambient pressure as 0 aswell ?

I would appreciate some explanations.