Setting Up Viscous Multiphase Flow

You can use the Viscous Multiphase model to simulate extrusion or co-extrusion applications.

The Viscous Multiphase model uses an interface capturing technique to model the motion of multiple viscous fluids on a fixed Eulerian mesh. You are advised to use the Viscous Multiphase model (instead of the Free Surface model) for modeling applications where you are expecting large deformations of the extrudate.

You are advised to use the Viscous Multiphase model in combination with the Free Surface model (see Extrusion and Free Surface Flow) under any of the following circumstances:

  • The approximate position of the interface between phases is not known and materials form an irregular interface inside the die.
  • Materials contact each other inside a complex die geometry that can form partial or full encapsulation.
  • Unbalanced flow of materials that leads to a large displacement of the interface from the specified initial position.

To set up viscous multiphase flow:

  1. For the physics continuum Continua > [physics continuum] > Models, select the following models, in order:
    Group Box Model
    Material Multiphase
    Multiphase Interaction (selected automatically)
    Multiphase Model Viscous Multiphase. See Viscous Multiphase Model Reference.
    Laminar (selected automatically)
    Viscous Flow (selected automatically)
    Conservative Level Set (selected automatically)
    Space Any
    Time Steady or Implicit Unsteady
    Optional Models If you want to consider heat transfer, select Viscous Energy
  2. Define each phase:
    1. Right-click the [physics continuum] > Models > Multiphase > Eulerian Phases node and select New.
    2. Right-click the [phase] > Models node and select the following models:
      Group box Model
      Rheology One of:
      • Generalized Newtonian
      • Thixotropic
      • Viscoelastic
      See Rheology Models Reference.
      Optional Models
    3. Expand the Liquid > [material] > Material Properties node and specify the material properties and rheological model parameters of the phase.
  3. To determine how the multiphase material mixture properties are calculated, expand the Multiphase > Mixture > Material Properties node and for each material property node—Density, Dynamic Viscosity, Thermal Conductivity—select one of the following mixture rules:
    • Field Function
    • Harmonic Rule of Mixture Method
    • Linear Rule of Mixture Method

    For Specific Heat, only the following are available:

  4. To specify initial conditions for the phase field:
    1. Select the [physics continuum] > Initial Conditions > Phase Field node and set Method to one of the following:
      • Composite
      • Composite N-1
      • Constant
    2. Then set Value to one of the following:
      • 0—The cell is not filled with the phase material.
      • 1—The cell is filled with the phase material.

      For the Constant method, specify the phase field values in the order that you created the phases: [phase 1, phase2, ...].

  5. Specify the phase field at the inflow boundary conditions:
    1. Select the [region] > Boundaries > [boundary] node and set Type to Velocity Inlet or Mass Flow Inlet node.
    2. Select the [boundary] > Physics Values > Phase Field node and set Value to one of the following:
      • 1—Inflow of the phase through the boundary.
      • 0—No inflow of the phase through the boundary.