VOF-Lagrangian Stripping

Lagrangian models track individual packets of finely dispersed particles through the domain, while VOF Multiphase models track the volume of two or more interpenetrating phases. When using both modeling techniques (for example, water droplets spraying through the air into a large volume of water), you can link the two forms of modeling with a Lagrangian Stripping model which is a type of phase interaction model.

To model VOF-Lagrangian Stripping:

  1. Start with a simulation that contains both Eulerian and Lagrangian phases, and has VOF multiphase activated for the Eulerian phase.
  2. Add the following models, in order:
    Node Group Box Model
    Lagrangian Multiphase > Lagrangian Phases > [free-stream phase] > Models Optional Models Two-Way Coupling
    Multiphase Interaction > Phase Interactions > [phase interaction] > Models Phase Interaction Topology VOF-Lagrangian Phase Interaction
    Optional Models VOF-Lagrangian User Stripping
  3. In the Properties window of the VOF-Lagrangian Phase Interaction node, select the Lagrangian and VOF phases to interact.
  4. Create an injector to introduce the Lagrangian particles.

One-way coupling between VOF and Lagrangian models is appropriate when the loading from the Lagrangian phase is small and can be neglected in the VOF solution. When the Two-Way Coupling model is selected in the Lagrangian phase models, the mass, momentum, and energy of parcels that impinge on the VOF phase are accumulated as part of the solution.

Lagrangian particles are introduced in cells adjacent to the VOF phase when stripping takes place. The mass, momentum, and energy of the VOF phase is reduced by the amount taken by the stripped particles.

VOF-Lagrangian User Stripping Model Reference

The VOF-Lagrangian User Stripping model allows you to select the diameter of the injected particles and the mass flux injected. The stripping model uses gradient information from the VOF model to find the free surface and the interaction area density (area per unit volume). The model creates particles on the surface when the following requirements are met:

  • The flow rate on the surface is large enough to create a parcel with a particle count of at least one.
  • There is enough mass in the cell from the VOF donor phase to create that parcel single parcel.

The particle diameter is limited to 50% of the cell length scale (the cube root of the cell volume). The Output window displays a warning, giving the number of cells in which particles have reached the 50% limit, for each time step. If diameter or mass flux settings result in unphysical results, the simulation proceeds but uses the maximum allowed values rather than the values specified.

The stripped parcel is placed at the centroid of the cell; particle temperature and mass fraction take their values from the VOF phase while the parcel velocity is derived from the cell velocity with an appropriate perturbation that moves it away from the free surface.

Selecting the VOF-Lagrangian User Stripping model automatically introduces a volume stripping injector. This injector uses the Time Randomization condition and the Parcel Streams value.

Provided By Multiphase Interaction > Phase Interactions > [interaction] > Models > Optional Models
Example Node Path Multiphase Interaction > Phase Interactions > [interaction] > Models > VOF-Lagrangian User Stripping
Requires Phase Interaction Topology: VOF-Lagrangian Phase Interaction
Activates Model Controls (child nodes) Diameter, Mass Flux.
Field Functions See Field Functions.
VOF-Lagrangian User Stripping Child Nodes
Diameter
Specifies the diameter of the injected particle using common scalar profile methods.
Mass Flux
Specifies the injected mass flux using common scalar profile methods.

Field Functions

Is Stripping
Whether stripping is occurring in a cell during a particular time-step.
The following field functions are made available to the simulation when the Temporary Storage Retained property is activated for the Lagrangian multiphase solver:
Interface Area Density of [Eulerian phase]
The interfacial area available for momentum, heat, and mass transfer from the Lagrangian phase to the continuous eulerian phase through phase interaction.
Interface Normal of [Eulerian phase]
The unit normal vector ( − ∇ α c ‖ ∇ α c ‖ ) pointing away from the Eulerian phase.