Fluid-Fluid Interface
The Fluid-Fluid Interface node defines the initial position of a fluid-fluid interface and includes equations to track the evolution of the interface. The Wall-Fluid Interface subnode is added by default, and is also available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
model input
Enter a value for the Temperature T (SI unit: K). This option is only necessary when the surface tension coefficient comes from a library of coefficients, as explained below.
Surface Tension
Select the Include surface tension force in momentum equation check box to include the surface tension force in the momentum equation.
The Surface tension coefficient σ (SI unit: N/m) can be User defined, or select Library coefficient, liquid/gas interface (default) or Library coefficient, liquid/liquid interface.
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For Library coefficient, liquid/gas interface select an option from the list — Water/Air (default), Acetone/Air, Acetic acid/Air, Ethanol/Air, Ethylene glycol/Ethylene glycol vapor, Diethyl ether/Air, Glycerol/Air, Heptane/Nitrogen, Mercury/Mercury vapor, or Toluene/Air.
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For Library coefficient, liquid/liquid interface select an option from the list — Benzene/Water, 20°C, Corn oil/Water, 20°C, Ether/Water, 20°C, Hexane/Water, 20°C, Mercury/Water, 20°C, or Olive oil/Water, 20°C.
Mass Flux
The mass flux setting specifies the mass transfer across the boundary, due to processes such as boiling. The default Mass Flux Mf (SI unit: kg/(m2·s)) is User defined, with a value of 0.
normal direction
The normal direction on the selected boundaries can be reversed by selecting Reverse normal direction. The direction is indicated by a red arrow in the Graphics window.
Location in user interface
Context Menus
Right click the physics interface and select Two-Phase Flow, Moving Mesh>Fluid-Fluid Interface
Ribbon
Physics tab with Laminar Flow selected:
Boundaries>Two-Phase Flow, Moving Mesh>Fluid-Fluid Interface
 
The Fluid-Fluid Interface feature imposes a mesh deformation in the normal direction. On adjacent boundaries, the mesh displacement parallel to those boundaries cannot be fixed if the contact point is moving. In this case a Mesh Slip, Symmetry/Roller, Prescribed Normal Mesh Displacement, or Prescribed Normal Mesh Velocity boundary condition under Definitions>Moving Mesh should be selected. A Mesh Slip condition is automatically used on boundaries that are adjacent to the Fluid-Fluid Interface and dot not have a prescribed Moving Mesh boundary condition.
If a Fluid-Fluid Interface feature is in contact with a solid boundary, the movement of the contact point is not compatible with the no slip condition. For laminar flow the Wall boundary condition with the Navier Slip option should be selected. For turbulence models with wall functions or automatic wall treatment the Wall feature with the No Slip option can be selected.