How should I set velocity outlet boundary conditions?
If you use Fixed value, you need to define velocity with respect to the coordinate system. This means, based on the flow direction, assign U_x, U_y, U_z and set (+) or (–) whether the direction is in positive or negative axis.
If you use flow rate, you need to define either
- Mass flow rate, or
- Volume flow rate
In this case, you need to define flow rate as negative to ensure that flow leaves the domain.