Modeling Eulerian Multiphase Flow

You use the Eulerian Multiphase (EMP) flow model if the phases are expected to be mixed on length scales smaller than the length scales to resolve, or if both stratified and dispersed two-phase flow coexist in the flow domain. In this model, each distinct phase has its own set of conservation equations. It is assumed that you are interested in the time averaged behavior of the flow, rather than the instantaneous behavior.

The phases in a Eulerian Multiphase (EMP) flow can be gas, liquid, or solid particles. Each phase has its own velocity, energy, and other variables, and its own physical properties. You define the phases and then define the interactions between the phases. This definition includes the models for the interfacial area, and for the rates of interphase transfer of mass, momentum and energy.

To set up a Eulerian Multiphase (EMP) flow simulation:

Create the physics continuum and choose the appropriate models.

Right-click Continua and click New > Physics Continuum.
The Physics 1 node is added.

Right-click Physics 1 > Models, click Select Models, and then, in the Physics Model Selection dialog, choose the following models:

Group Box

Model

Space

Select one of :

Axisymmetric
Three Dimensional (required for Adaptive Mesh)
Two Dimensional

Time

Select one of :

Steady
Implicit Unsteady

Material

Select one of :

Gas
Particle
Liquid
Multi-Component Gas
Multi-Component Liquid
Multi-Component Particle

Multiphase

Multiphase Interaction (selected automatically)

Multiphase Model

Eulerian Multiphase (EMP)

See Eulerian Multiphase (EMP) Model Reference

Gradients (Selected automatically)

Viscous Regime

Select one of :

Laminar
Turbulent

EMP Turbulence (required for Turbulent)

Select one of :

Mixture Turbulence
Models turbulence for the mixture. Use this method when the mixture turbulence represents the turbulence of both phases equally well, such as in bubbly flows. This method can be more robust in cases where the dispersed phase volume fraction is very low, as solving for the dispersed phase turbulence can cause numerical issues.
注
Mixture turbulence is not compatible with suspension rheology, emulsion rheology, and granular models.

See Modeling Mixture Turbulence.
Phasic Turbulence
Models turbulence for individual phases. Use this method when the dispersed phase behaves differently to the continuous phase, such as in droplet or particulate flows.
See Modeling Phasic Turbulence.

For counter-current flow where one phase is moving opposite to the other, you are recommended to use phase turbulence instead of mixture turbulence.

Optional Models

Phase Coupled Fluid Energy

If you want to apply automated time-step control, select Adaptive Time-Step and set the Adaptive Time-Step solver properties.

See Setting Up Adaptive Time-Stepping.

Adaptive Mesh—Use this model if you want to refine the mesh locally and select user-defined refinement criteria that query the flow solution as the simulation runs to control solution fidelity.

Select the User-Defined Mesh Adaption criteria and specify the appropriate properties.

See Adaptive Mesh Refinement.

Select the Models > Eulerian Multiphase (EMP) node and set the Volume Fraction Convection and the Velocity Convection properties.
See Eulerian Multiphase (EMP) Properties.
Depending on the flow regime that you want to model, do one of the following:
- If you want to model bubble and droplet flow where one liquid or gas phase is dispersed within another liquid or gas phase throughout the domain at all times, follow the additional steps described in Modeling Bubbly and Droplet Flows.
- If you want to model multiple flow regimes where both stratified and dispersed two-phase flows co-exist in the domain, follow the additional steps described in Modeling Multiple Flow Regimes.
- If you want to model particulate flows where the continuous phase is either gas or liquid and the dispersed phase consists of solid particles, follow the additional steps described in Modeling Particulate Flows.

Specify the initial conditions of each phase, typically the velocity and the volume fraction:

Select the Multiphase > Eulerian Phases > [phase] > Initial Conditions node and specify the Velocity and Volume Fraction values.
For multi-component phases, set the Species Specification method, and then specify the initial mass fraction or molar fraction of each component of the phase.
The volume fractions (and the species mass fractions or mole fractions, for multi-component phases) should sum to 1.0.
Simcenter STAR-CCM+ automatically normalizes the volume fractions if:
- the volume fractions sum to greater than 1.0.
- the volume fractions sum to less than 1.0, but are all non-zero values.
See Setting Initial Conditions.
Specify the boundary conditions and values for each phase.
See Setting Boundary Conditions.
To specify region conditions and values, expand the Regions > [region] > Phase Conditions > [phase] node and set:
- Energy Source Option
- Mass Source Option
- Momentum Source Option
- Turbulence Source Option
See Region Settings.
Set the solver parameters.

The under-relaxation factors are important and are common to all solvers. The other settings are typically used for troubleshooting.

See Setting the Solver Parameters.
(Optional) To evaluate the normalized phase mass conservation error in the simulation, right-click the Reports node and select New > Flow/Energy > Normalized Phase Mass Conservation Error , select the phase for which you want to assess the error, then create the corresponding monitor and plot.

You can use the normalized phase mass conservation error to evaluate the simulation convergence, or as a monitor for an adaptive stopping criterion to optimize simulation runtime. For more information, see Normalized Phase Mass Conservation Error.
Set up any reports, monitors, plots, and scenes that you require.

For example, to determine the forces or moments exerted by the phases on a boundary, you can create a monitor and plot the Force (EMP) or Moment (EMP) reports. Additionally, you can monitor the Volume Fraction of each phase.
Run the simulation.