Setting up the Phase Interactions

Water and air enter the domain as a dispersed mixture. You select the Multiple Flow Regime Topology phase interaction with water as the primary phase and air as the secondary phase. This implies that, in the first regime, air is dispersed in water (forming bubbles), while in the second regime, water is dispersed in air (forming droplets), and there is no clear dispersed phase in the intermediate regime. The diameter of the air bubbles is 1 mm and the diameter of the water droplets is 0.2 mm.

In this tutorial, it is anticipated that a large interface will form between phases. Therefore, you select the Large Scale Interface Detection phase interaction model, the Gradient Corrected Standard weight function, and the Adaptive Interface Sharpening (ADIS) volume-fraction convection scheme to model the large scale interface between the phases. The ADIS discretization scheme is appropriate for multiphase simulations where sharp interfaces and dispersed mixtures coexist between the same pair of phases as it uses a high-resolution interface capturing (HRIC) scheme in the vicinity of a large scale interface and a standard total variation diminishing (TVD) scheme away from it.

To define the phase interactions:

  1. In the Physics 1 continuum, right-click the Models > Multiphase Interaction > Phase Interactions node and select New > Water > Air (Multiple Flow Regime).
  2. Rename the Phase Interaction 1 node to Water-Air.
  3. Right-click the Water-Air > Models node and, in the Optional Models group box select Large Scale Interface Detection.
    The default properties of the Large Scale Interface Detection model and Interaction Area Density are appropriate for air-water flows.
  4. Edit the Water-Air > Models > Interaction Length Scale node and set the following properties:
    Node Property Setting
    First Dispersed Regime Interaction Length Scale Method Constant
    Value 0.001 m
    Second Dispersed Regime Interaction Length Scale Method Constant
    Value 2.0E-4 m

    The First Regime Interaction Length Scale specifies the typical size of the air bubbles that are dispersed in the water. The Second Regime Interaction Length Scale specifies the typical size of the water droplets that are dispersed in the air.

  5. Select the Water-Air > Models > Multiple Flow Regime > Flow Regime Weight Function node and set Method to Gradient Corrected Standard.
  6. Select the Physics > Models > Eulerian Multiphase (EMP) node and set the following properties:
    Property Setting
    Volume Fraction Convection Adaptive Interface Sharpening (ADIS)
    Minimum Volume Fraction 1.0E-10
    To increase the robustness of the simulation, you set the minimum volume fraction to a value greater than zero.
  7. Save the simulation.