Surface Tension Force Model Reference

$σ$ is defined as the amount of work necessary to create a unit area of free surface.

Surface tension always exists between a given pair of fluids. Its magnitude depends on the nature of the fluids in contact as well as on temperature. The experimentally determined surface tension coefficient $σ$ expresses the ease with which the fluids can be mixed. For immiscible fluids, the value is always positive.

In the current implementation, each phase interaction is assigned its own surface tension coefficient. This coefficient is used to calculate the surface tension force between each of the phases in the phase interaction.

This implementation implies that, in general:

The model works correctly in multiphase flows (more than two phases can be present).
Different surface tension coefficients can be assigned to each phase interaction.

The calculation of the free surface curvature is sensitive to mesh quality. Therefore, to get good results even on coarse grids, you are recommended to use Cartesian meshes.

Table 1. Surface Tension Force Model Reference
Theory	See Surface Tension.
Provided By	[phase interaction] > Models > Optional Models
Example Node Path	[phase interaction] > Models > Surface Tension Force
Requires	Physics continuum selections: Material: Multiphase Multiphase Model: Eulerian Multiphase (EMP) (Automatically activates: Multiphase Interaction, Gradients.) A Multiple Flow Regime Topology phase interaction is required.
Properties	None.
Activates	Model Controls	Primary Phase Artificial Viscosity Coefficient Secondary Phase Artificial Viscosity Correlation See Surface Tension Force Child Nodes.
	Materials	Surface Tension See Materials and Methods.
	Boundary Inputs	Contact Angle See Boundary Settings.
	Field Functions	See Field Functions.

Surface Tension Force Child Nodes

The discretization of the surface tension force term across a sharp interface between phases can lead to errors that manifest themselves as parasitic currents. You can mitigate this problem by adding an artificial viscosity component.

See Applying Artificial Viscosity.

Primary Phase Artificial Viscosity Coefficient

The primary phase artificial viscosity per interaction area density. This value has units of dynamic viscosity per interfacial area density [Pa-m-s] and can be specified as a constant or field function. The default value is 0 Pa-m-s.

This value is ${\hat{μ}}_{a r t, p}$ in Eqn. (2327).

Secondary Phase Artificial Viscosity Correlation

The artificial viscosity correlation ratio with regards to the primary phase. The default value is 1.0.

This value is $r_{s}$ in Eqn. (2328).

Secondary Phase Artificial Viscosity Correlation Method: The available methods are Constant or Field Function.
Value/Scalar Function: The constant value or scalar field function that provides the artificial viscosity correlation ratio.

Materials and Methods

Surface Tension: The surface tension force appears as a material property for the phase interaction. It is entered as a scalar profile.

Boundary Settings

Wall Boundaries

Contact Angle

Allows you to specify the capillarity effect at the boundary.

Method	Corresponding Physics Value Nodes
Kistler Implements the Kistler correlation. The function is valid for contact angle values in the range 0–176 degrees. Advancing or receding contact angles that are larger than the upper bound are limited to 176 degrees. See Kistler Correlation.	None

Field Functions

Capillary Number of [phase interaction]: This scalar field function is defined at wall boundaries and can be used in the definition of a user field function to specify your own user-defined dynamic contact angle correlation.
Contact Angle of [phase interaction]: The surface tension contact angle. This scalar field function is defined at wall boundaries.