Phase Field For the phase field method, the motion of the interface on the boundary due to advection is zero and so the No-slip boundary condition is used in the momentum equation u = 0. The following boundary condition defines the contact angle between Fluid 2 and the wall:

where w is the user-defined contact angle and n is the unit vector normal to the wall. The phase field help variable is assigned the boundary condition:

With the phase field method, enter a value or expression for the Contact angle w. The default value is pi/2 ( /2) rad.

Moving Wetted Wall

When the wetted wall is moving, Equation 6-1 and Equation 6-2 are still valid but the boundary condition for the momentum equation becomes u = uw. Enter a value or expression for these properties:

•The components of the Velocity of the moving wall uw (SI unit: m/s).

•The Contact angle w. The default is pi/2 ( /2) rad.

C O N S T R A I N T S E T T I N G S

To display this section, click the Show button () and select Advanced Physics Interface Options. Select a Constraint type—Bidirectional, symmetric or Unidirectional. Select the Use weak constraints check box as required.

The Moving Wetted Wall boundary condition is only available when using

the phase field method.

Note

Initial Interface

Use the Initial Interface node to define the initial position as a boundary condition on interior boundaries. During the initialization step, this boundary condition sets the level set function to 0.5 or the phase field function to 0. Transient simulations of the fluid flow treats the boundary as an interior boundary.

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B O U N D A R Y S E L E C T I O N

From the Selection list, choose the interior boundaries that represent the initial

fluid-fluid interface.

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