Controlling Phase Interactions in VOF Simulations

You create and define the appropriate VOF phase interactions.

The procedure for creating a phase interaction is described in Creating a Phase Interaction.

The following phase interaction models are available in VOF simulations:

VOF-VOF Phase Interaction model, which controls the interaction between two VOF phases.
Film-VOF Phase Interaction model, which controls the interaction between the fluid film phase and a VOF phase.
This model is available only when the Fluid Film model is activated in the physics continuum.
VOF-Lagrangian Phase Interaction model, which controls the interaction between a VOF phase and a Lagrangian phase.
This model is available only when the Lagrangian Multiphase model is activated in the physics continuum.

A phase interaction model becomes available when both of the relevant phases exist.


Phase Combination Modeled	Physical Phenomena Modeled
Gas-Liquid	Evaporation Condensation Boiling Cavitation Gas Dissolution
Liquid-Solid	Melting Solidification

The primary and secondary phases are specified when you create the phase interaction, but you can change them if necessary. These settings affect the optional models that are made available.

To change the primary and secondary phases:

Select the [phase interaction] > Models > VOF-VOF Phase Interaction node and set the appropriate phases:

Define the phase interaction.

Reopen the Phase Interaction Model Selection dialog and select the appropriate optional models for the phase interaction.

Mass Transfer Models:


Model	Relevant information
Evaporation/Condensation	See Modeling Evaporation and Condensation.
Boiling	Two models are available: Rohsenow Boiling and Transition Boiling See Modeling Boiling.
Cavitation	Three models are available: Full Rayleigh-Plesset, Homogeneous Relaxation, and Schnerr-Sauer. See Modeling Cavitation.
Gas Dissolution	See Modeling Gas Dissolution.
Melting and Solidification	See Modeling Melting and Solidification.
Interphase Reaction	Interphase reactions are modeled with the Interphase Reaction model. Both of the phases must be multi-component. See Interphase Reaction Model Reference.

Other models:


Model	Relevant information
Slip Velocity	See Slip Velocity Model. The Slip Velocity model can be unstable in some situations, especially for a large interaction length scale. Two ways that you can resolve the problem are outlined below. These methods are applicable only to Drag-based slip. Set the Phase Slip Velocity solver Under-Relaxation Factor. Smaller under-relaxation values provide more stability, but also give slower convergence. Set the Phase Slip Velocity solver Body Force Smoothing Iterations. Higher values provide a more uniform distribution of specific body forces and therefore more stability, but also decrease the local resolution of body forces. See Phase Slip Velocity Solver Properties.
Contact Time	See Using the Contact Time Model.
Interaction Area Density	See Interaction Area Density Model Reference.
Interaction Length Scale	See Interaction Length Scale Model Reference.
Interface Turbulence Damping	This model is useful in simulations that contain a liquid-gas interface with a high relative velocity between the phases. For example, the flow of water on the windows of a moving vehicle: the water flow is slow and dominated by surface tension, but the air flow velocity can be high and aerodynamic forces are significant. The K-Omega Turbulence, K-Epsilon Turbulence or Reynolds Stress Turbulence model must be activated in the physics continuum. Set the appropriate damping coefficient method and value. See Interface Turbulence Damping.
Interface Momentum Dissipation	See Using the Interface Momentum Dissipation Model.
VOF Phase Replacement	See Replacing VOF Phases.
Surface Tension Force	See Modeling Surface Tension.
Macro Porosity (fully coupled) and Macro Porosity (pure thermal)	See Detecting Shrinkage-Related Defects.

A VOF-VOF Phase Interaction allows multiple flow regimes (dispersed primary phase, dispersed secondary phase, intermediate regime). Values such as drag are calculated with a weighted sum of the interaction of each flow topology regime. You specify the blending function that is used in the transition between flow regimes.

Select the [phase interaction] > Models > VOF-VOF Phase Interaction > Flow Regime Weight Function node and set Method to one of the following options:
- Gradient Corrected Standard
- Standard
- User Specified
See Flow Regime Weight Function Properties.

The VOF-Lagrangian Phase Interaction model allows you to select the phases involved in the interaction when Lagrangian particles impinge on or strip from a VOF surface. If you want to simplify relatively small VOF blobs by using Lagrangian parcels, use the Resolved VOF-Lagrangian Transition model.

Define a VOF-Lagrangian phase interaction.

Right-click the [phase interaction] > Models node and click Select Models.
In the model selection dialog, activate the following models in order:


Group Box	Model
Optional Models	Resolved Transition—identifies large blobs that move through the VOF field with significant momentum and velocity (also known as ballistic blobs) and transitions them into computationally more efficient LMP particles. See Resolved Transition. VOF-Lagrangian User Stripping—models the Lagrangian particles stripping from a VOF surface. The VOF-Lagrangian User Stripping model allows you to select the diameter of the injected particles and the mass flux injected. See VOF-Lagrangian Stripping. Impingement—models the impingement of a Lagrangian phase on to an VOF Eulerian phase. See Modeling Impingement.