Setting Initial Conditions

When you use multiple Eulerian phases in a simulation, you need to set the initial volume fraction of each phase in the physics continuum.

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.

However, if the volume fractions sum to less than 1.0 and include a zero value, Simcenter STAR-CCM+ displays an error message.

To set the initial volume fraction of each phase:
  1. Select the [physics continuum] > Initial Conditions > Volume Fraction node, select the appropriate method (Composite, Composite N-1, or Constant), and then set the value for each phase.

    For descriptions of the available methods, see Arrays of Scalar Quantities.

For multi-component phases, you also specify the initial mass fraction or molar fraction of each component of the phase.

  1. For each phase, select the [physics continuum] > Models > Multiphase > Eulerian Phases > [phase] > Initial Conditions node, set the Species Specification, and then specify the initial conditions for the mass fraction or molar fraction of each component of the phase.
For each region, you can use the continuum values, or set specific values for the region.
  1. Select the [region] > Physics Conditions > Initial Condition Option node and set Option to Use Continuum Values or Specify Region Values.
If you choose to specify region values, set the initial volume fraction for each phase in the region.
  1. Select the [region] > Initial Conditions > Volume Fraction node and set the appropriate values.

For multi-component phases, you also specify the initial mass fraction or molar fraction of each component of the phase.

  1. Select the [region] > Initial Conditions > Phase Conditions > [phase] > Initial Conditions node, set the Species Specification, and then specify the initial conditions for the mass fraction or molar fraction of each component of the phase.

    To improve convergence, you should always specify initial values of mass fraction or molar fraction for every phase, including any phases that are empty initially (that is, the initial volume fraction of the phase is 0.0). For a phase that is empty initially, it is recommended that you set the initial mass fraction to the mass fraction values that the phase has when it enters the solution domain.