Use the Vortex Sheet boundary condition to model a shear layer that separates a stream from the free velocity field. Because the velocity potential is discontinuous over this boundary. Vortex sheets are only applicable on interior boundaries or between assemblies.

where w denotes the outward normal displacement (SI unit: m) of the vortex sheet surface. The condition ensures continuity in the normal stress (the pressure) and the normal displacement, while allowing for a slit (jump) in the tangential component of the total velocity.

On pair (interior) vortex sheet conditions the up/down, that refers to the up and down side of an interior boundary, is replaced by a 1 and 2 index in the equation display (referring to the two faces in the pairs).

This boundary condition adds and additional degree of freedom lpff.vs1.w (here using the default name for the physics interface and boundary condition) which is solved for.