Setting Initial Conditions and Reference Values

Set the initial conditions and reference values for the physics continuum.

The initial volume fractions of water and air are specified as scalar functions. The steam generator is partially full of water, with the initial water level indicated in the diagram below:



To set the initial conditions and reference values:

  1. Define the field function to use for specifying the initial volume fraction of water:
    1. Right-click the Automation > Field Functions node and select New > Scalar.
    2. Rename the User Field Function 1 node to Initial_VF_Water.
    3. Select the Initial_VF_Water node and set the following properties:
      Property Setting
      Function Name Initial_VF_Water
      Definition ($${Centroid}[0]>2.67) ? (($${Centroid}[1]<0.230) ? 1.0 : 0.0 ) : 0.0
  2. Define the field function to use for specifying the initial volume fraction of air:
    1. Create another scalar field function and rename it to Initial_VF_Air.
    2. Select the Initial_VF_Air node and set the following properties:
      Property Setting
      Function Name Initial_VF_Air
      Definition 1.0-${Initial_VF_Water}
  3. Edit the Continua > Physics 1 > Models > Multiphase > Phases node and set the following properties:
    Node Property Setting
    Water > Initial Conditions > Volume Fraction Method Field Function
    Scalar Function Initial_VF_Water
    Air > Initial Conditions > Volume Fraction Method Field Function
    Scalar Function Initial_VF_Air

Multiple Flow Regimes phase interactions do not have a clear reference phase because either of the phases can be dispersed in the other phase. In this scenario, the density variation can be significant (several orders of magnitude) and can result in numerical instabilities. To obtain a robust and stable numerical solution, set the reference density to zero. This setting ensures that the full body force due to gravity is used in the momentum equation.

Set the reference value for the Physics 1 continuum:

  1. Edit the Continua > Physics 1 > Reference Values node and set the following property:
    Node Property Setting
    Reference Density Value 0.0 kg/m^3
  2. Save the simulation.