Modeling Impingement

The Impingement model in Simcenter STAR-CCM+ allows you to simulate the impingement of a droplet or bubble, represented by a Lagrangian phase, onto a corresponding liquid or gas, modeled using either a VOF or an MMP phase. The model predicts the impingement rate and formation of VOF or MMP phase from the Lagrangian droplets/bubbles based on the defined impingement criteria.

The following are required:

A Mixture Multiphase (MMP) or a Volume of Fluid (VOF) Multiphase simulation with the Lagrangian Multiphase model activated.
VOF or MMP phases and Lagrangian phase defined.

To model impingement:

Start with a simulation that contains both Eulerian and Lagrangian phases, and has VOF multiphase or MMP multiphase activated for the Eulerian phase.

For consistency, use the same materials for the Eulerian and Lagrangian phases.

Add the following models, in order:


Node	Group Box	Model
Lagrangian Multiphase > Lagrangian Phases > [Lagrangian free-stream phase] > Models	Optional Models	Two-Way Coupling
Multiphase Interaction > Phase Interactions > [phase Interaction] > Models	Phase Interaction Topology	VOF-Lagrangian Phase Interaction See VOF-Lagrangian Phase Interaction.
	Phase Interaction Topology	MMP-Lagrangian Phase Interaction See MMP-Lagrangian Phase Interaction.
	Optional Models	Impingement See Impingement.

One-way coupling between VOF/MMP and Lagrangian models is appropriate when the loading from the Lagrangian phase is small and can be neglected in the VOF/MMP 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/MMP phase are accumulated as part of the solution. During the simulation, free-stream Lagrangian particles are deleted after impinging on any cells where the VOF/MMP solution fulfills the respective multiphase model impingement criterion. Parcels that are absorbed transfer their mass, momentum, and energy to this VOF/MMP phase. If Two-Way Coupling is activated and source smoothing is used in the Lagrangian Multiphase solver, source smoothing is also applied to source terms resulting from the impingement.

(Optional) To prevent the Lagrangian volume fraction from exceeding the specified maximum value, you are advised to use volume cell cluster source smoothing.
1. Select the Two-Way Coupling > Volume Source Smoothing Method node and set Method to Cell Cluster.
2. Select the Volume Source Smoothing Method > Cell Cluster > Cluster Length node and set the appropriate value.
Set up the phase interactions:
1. For a VOF-Lagrangian phase interaction, in the Properties window of the VOF-Lagrangian Phase Interaction node, select the Lagrangian and VOF phases to interact.
2. For an MMP-Lagrangian phase interaction, in the Properties window of the MMP-Lagrangian Phase Interaction node, select the Lagrangian and MMP phases to interact.
3. For an MMP-Lagrangian phase interaction, select the MMP-Lagrangian Phase Interaction > Volume Fraction Threshold node and set Value to define the volume fraction limit for the impingement of the Lagrangian phase onto the MMP continuous phase.
  
  See Impingement Properties.

You specify a VOF or MMP conversion boundary interaction mode for the Lagrangian phase which definines how particles behave when they impinge on a dry wall. The particles' mass, tangential momentum, and energy transfer to an MMP or VOF phase in cells on the wall boundary.

To set up the boundary interaction mode globally for all boundaries:
1. For a VOF-Lagrangian phase interaction, in the Lagrangian phase, select the Boundary Conditions > [boundary] > Physics Conditions > Mode node and set Active Mode to VOF Conversion.
2. For an MMP-Lagrangian phase interaction, in the Lagrangian phase, select the Boundary Conditions > [boundary] > Physics Conditions > Mode node and set Active Mode to MMP Conversion.
To set the boundary interaction mode locally for specific boundaries:
1. For the wall or baffle boundary, select the Physics Conditions > Lagrangian Specification node and set Method to Specify for Boundary.
2. Select the Phase Conditions > [phase] > Physics Conditions > Mode node and set Active Mode to VOF Conversion or MMP Conversion.
  
  When you select the VOF or MMP conversion interaction modes for a boundary, impingement occurs in cells adjacent to the boundary, even if the impingement criterion is not satisfied.