The Wall Fluid Interface subnode is available from the context menu (right-click the Fluid-Fluid Interface and External Fluid Interface parent node) or from the Physics toolbar, Attributes menu. The condition applies forces on the wall that balance the surface tension for the prescribed contact angle. Note that the contact angle can only be enforced when the surface tension force is included in the momentum equation in the parent feature.

For laminar flow, the Wall-Fluid Interface node should be used on edges or points where a Wall feature with the Navier Slip option is prescribed adjacent to the free surface. In this case, the Navier Slip option is required for the contact line to move along the wall.

Select an option from the Specify contact angle list — Directly (the default) or Through Young’s equation.

Select whether to Constrain the wall-normal velocity. This ensures that the fluid velocity normal to the wall on the contact edge or point is exactly the desired value. This can be helpful when the adjacent wall uses a Discontinuous Galerkin Formulation and the no-penetration condition is satisfied in an integral sense rather than pointwise. Moreover, constraining the wall-normal velocity simplifies the equilibrium of forces in the wall-normal direction. This setting should not be selected when the adjacent boundary has an unknown velocity.