Transitioning Eulerian Blobs to Lagrangian Particles

In simulations where a Eulerian phase forms blobs, you can represent them as Lagrangian particles instead of as the resolved Eulerian phase.

Converting Eulerian blobs into Lagrangian particles can be more efficient, as tracking a resolved Eulerian particle requires a fine mesh along its entire path and is computationally more expensive than tracking a Lagrangian particle, particularly when the Lagrangian particle is crossing coarser mesh. See Resolved Transition.

You use the Resolved Transition phase interaction model to identify the emerging blobs and automatically transition them into equivalent mass Lagrangian particles. You are advised to use adaptive mesh refinement (AMR) to locally refine the blob phase interface or locally coarsen the mesh for tracking of the Lagrangian particle and further enhance computational efficiency.

Note	A blob is not converted into a Lagrangian particle if the blob is attached to a boundary. In this scenario, the blob continues to be represented as a Eulerian phase, even when the blob satisfies all the criteria defined under the Eulerian-Lagrangian Trasition Criteria node.

You require a VOF or MMP Multiphase simulation with the Lagrangian Multiphase model activated.

To resolve Eulerian blobs as Lagrangian particles:

Define the transition Eulerian phase and set the Material as Gas, Multi-Component Gas, Liquid or Multi-Component Liquid.

See Defining the Eulerian Phases.
Define the Lagrangian phase:
1. Set the Material as Gas, Multi-Component Gas, Liquid or Multi-Component Liquid, as in the Eulerian phase.
2. Set the Particle Type as Material Particles.
3. Activate the Two-Way Coupling model.
See Lagrangian Phase Models.
Create the Eulerian-Lagrangian Phase Interaction:
1. Right-click the Multiphase Interaction > Phase Interactions node and select New > [phase] > [Lagrangian phase].
2. Open the Phase Interaction Model Selection dialog and, in the Optional Models group box, activate Resolved Transition.
3. Select the Resolved Transition > Eulerian-Lagrangian Transition Criteria node and set the Blob Diameter Criterion, Blob Shape Criterion, and the Minimum Blob Volume Fraction Criterion transition criteria.
  Blob Diameter Criterion, Blob Shape Criterion, and the Minimum Blob Volume Fraction Criterion are defined as default, and can be removed if they are not required.
4. If you want to specify a user-defined criterion, right-click the Resolved Transition > Eulerian-Lagrangian Transition Critera node and select a new User Defined Criterion.
  Use a User Defined Criterion to set local blob transition criteria, for example, for each cell or parcel.
  
  The Resolved Transition Model determines which Eulerian blobs transition to Lagrangian parcels by checking the multiple criteria that you defined. Eulerian-Lagrangian transition takes place only for Eulerian blobs that satisfy all the criteria.
See Resolved Transition Model Reference.

Create a volume stripping injector to inject Lagrangian particles that are generated by the resolved transition:

Right-click the Injectors node and select New.

Select the Injectors > Injector 1 node and set the following properties:

Property	Setting
Lagrangian Phase	The transitioning Lagrangian phase.
Type	Volume Stripping Injector
Inputs	The regions in which the Eulerian-Lagrangian transition is active.

To set the maximum volume fraction of the Lagrangian particles in a cell, select the Solvers > Lagrangian Multiphase > Two-Way Coupling node and set Maximum Volume Fraction to the appropriate value.

The Resolved Transition model evaluates the Lagrangian volume fraction after the transition and, if the evaluated value does not exceed the specified Maximum Volume Fraction, the blob is converted to a Lagrangian particle. If the evaluated value exceeds the specified Maximum Volume Fraction, the transition does not occur and the Eulerian blob remains as a resolved VOF or MMP phase.

For more information, see Two-Way Coupling Solver.
For Mixture Multiphase (MMP) simulations, to activate the Adaptive Interface Sharpening (ADIS) convection scheme, select the [physics continuum] > Mixture Multiphase node and set Convection to Adaptive Interface Sharpening (ADIS).
The Resolved Transition model requires the use of the ADIS convection scheme for MMP simulations to maintain sharp interfaces between the Eulerian phases.
(Optional) To prevent the Lagrangian volume fraction from exceeding the specified maximum value, it is recommended that you use volume cell cluster source smoothing.
1. Select the Two-Way Coupling > Volume Source Smoothing Method node and set the method to Cell Cluster.
2. Select the Volume Source Smoothing Method > Cell Cluster > Cluster Length node and set the appropriate value.
  
  A suitable value for the cluster length is twice the transition length scale. When you use this value, the expected maximum Lagrangian volume fraction that is transitioned from an Eulerian blob is approximately 0.1.
(Optional) Set up free surface mesh refinement or AMR criteria that are designed for VOF multiphase simulations.

This model can dynamically refine the mesh near the interface and Eulerian blobs and, at the same time, locally coarsen the mesh after a Eulerian blob is converted into an LMP particle.
1. Open the Physics Model Selection dialog and, in the Optional Models group box, activate the Adaptive Mesh model.
2. Right-click the Adaptive Mesh > Adaptive Mesh Criteria node and select New > Free Surface Mesh Refinement.
See Setting Up Free Surface Mesh Refinement.
(Optional) Set up AMR criteria designed for MMP multiphase simulations.

For MMP simulation with Resolved Transition, you use User-Defined Mesh Adaption to capture the interface between the Eulerian phases. This refines the mesh based on a user-specified blob phase volume fraction Range (for example [0.001-0.999] ), and coarsens the mesh in regions where the blobs are converted into LMP droplets.
1. Right-click the Adaptive Mesh > Adaptive Mesh Criteria node and select New > User-Defined Mesh Adaption.
2. Select the [user-defined mesh adaption] > Adaption Request node and set Scalar Function to Volume Fraction of [blob phase].