The tutorial simulates two-dimensional gravity-driven flow through a channel connecting two chambers, as shown below. Initially, the chamber on the left is filled with water; the one on the right and the connecting channel with air. All boundaries are solid walls except for the horizontal top surfaces where a constant (atmospheric) static pressure is applied.
Under the action of gravity, water flows into the right chamber under assumed turbulent conditions. At the same time, water also flows in through the top left boundary so as to maintain a constant fluid level. After some time, the free surface on the right chamber settles at the level of the top boundary in the left chamber.