Setting Initial Conditions and Reference Values

Set the initial conditions and reference values for the physics continuum. You define field functions to use for specifying the initial condition for the spatial distribution of the two fluids in the continuum.

The usual practice for initially stationary fluids is to specify low, non-zero values for the turbulence parameters. If these quantities are set to zero, numerical problems can arise.

The initial condition for the spatial distribution of the two fluids in the continuum is that you only have water in the left-hand chamber and only air in the right-hand chamber and channel. Both fluids are also stationary. A convenient way of specifying such a distribution is by creating and using field functions.

The direction and magnitude of the gravity vector are set using the Reference Values node. In this case, a gravity force is applied in the negative y-direction.

To set the initial conditions and reference values:

Define the field function to use for specifying the initial condition for the spatial distribution of the water in the continuum:
  1. Right-click the Automation > Field Functions node and select New > Scalar from the pop-up menu.
  2. Rename the User Field Function 1 to Initial Distribution.
  3. Select the Initial Distribution node and set the following properties:
    Property Setting
    Function Name Initial Distribution
    Definition ($$Position[0]<=-1)?1:0
Define the field function to use for specifying the initial condition for the spatial distribution of the air in the continuum:
  1. Create another scalar field function and rename it to Initial Distribution (Air).
  2. Select the Initial Distribution (Air) node and set the following properties:
    Property Setting
    Function Name Initial Distribution (Air)
    Definition 1-${Initial Distribution}
Set the initial conditions and reference values for the Chambers continuum.
  1. Edit the Initial Conditions node and set the following properties:
    Node Property Setting
    Turbulence Intensity Value 0.01
    Turbulent Viscosity Ratio Value 100.0
    Volume Fraction Method Composite
    Composite > H2O Method Field Function
    Scalar Function Initial Distribution
    Composite > Air Method Field Function
    Scalar Function Initial Distribution (Air)


  2. Edit the Reference Values node and set the following properties:
    Node Property Setting
    Gravity Value [0.0,-9.81] m/s^2
  3. Save the simulation.