Inflow and Outflow are referred to as "open" boundaries, across which the convection of fluid occurs. At open boundaries, user need provide boundary conditions to specify the status of the fluid and flow outside the boundary, which is defined at the "ghost cells". Boundary conditions in the ghost cells are closely related to and affect the fluid and flow status in the interior fluid cell.

Ansys Forte offers the varieties of inflow and outflow boundaries:

There are both commonalities and differences in their assumptions and implementations. In this section, we first describe General Treatment that are common to all these options, then describe the distinct features, usage, and input requirements for each of these in the following subsections.