Outlet
The Outlet node adds a boundary condition for the outflow (or inflow) perpendicular (normal) to the boundary. It has different options that can be used to specify inlet condition on a boundary, as follows:
Velocity
Enter a value or expression for the Normal outflow velocity U0 (SI unit: m/s). A positive value of U0 represents an outflow velocity whereas a negative value represents an inflow velocity.
where U0 is a specified value or expression for the outward (or inward) Darcy velocity.
Pressure
Similar to the inlet Pressure option, the outlet pressure on a boundary can be specified. Enter a value or expression for the Pressure p0 (SI unit: Pa).
Discharge
Enter a value or expression for the discharge QD to specify the volumetric flow rate through the boundary. The mass flux ρu is related to the discharge as follows:
(7-8).
The mean normal outflow velocity at the boundary can then be calculated as Uout = QD/A, where A is the cross sectional area of the boundary.