The Surface Tension feature adds the necessary condition to model an interface between two fluids including surface tension effects. Add this node from the Interior Conditions submenu. This acoustic (perturbation) formulation of the Young-Laplace equation relies on a linearization around the stationary shape of the interface. The feature is important when modeling small curved interfaces between two different immiscible fluids, like microbubbles or microdrops.

where σ is the surface tension coefficient, T is the total stress in the fluid, and κaco is the acoustic perturbation to the steady state curvature of the interface. The steady state main curvatures of the interface are κ1 and κ2. The normal acoustic displacement of the interface is dn.

Select the Surface tension coefficient from the list of built-in options or enter a user-defined value. Select to pick from the Library coefficients, for liquid/gas interfaces and then select from the built-in list, pick from the Library coefficients, for liquid/liquid interfaces and select from the built-in list, or select User defined. For User defined enter the surface tension coefficient σ (SI unit: N/m).