Use the Border node to set a pressure condition at the border and the border flow type.

The Border flow condition is used to account for the pressure drop caused by the flow converging into the gap, outside the thin layer. The acoustic elongation options does this by adding additional thickness to the thin layer beyond the edge of the geometry (assuming a pressure gradient in this layer equal to that at the boundary). The Out-of-plane motion calculates the pressure gradient due to circulation of the fluid caused by motion of the wall or base surfaces using a predefined model. Alternatively the pressure gradient at the boundary can be specified using an arbitrary expression, which allows for more sophisticated, user-defined models.

Select a Border condition — Zero pressure (the default), Pressure, or Border flow. When the Cavitation check box is selected for the physics interface, Starvation is also available.

For Pressure enter a Pressure pf0 (SI unit: Pa) to define pf = pf0 on the boundary, edge, or point. The default is 0 Pa. If the reference pressure pref, defined at the physics interface level is 0, pf0 is the absolute pressure. Otherwise, pf0 is the relative pressure.

For Border flow select a Border flow type — Acoustic boundary condition-absolute elongation, Acoustic boundary condition-relative elongation, Out-of-plane motion, or User defined.