Applying Flow Sources and Sinks

In a flow simulation, you can apply sources and sinks for momentum and mass. Momentum sources are useful for modeling fans or for adding specific volumetric forces. With mass sources, you can add extra mass to the flow domain, such as for modeling mass injection.

To add a momentum source to a region:
  1. Select the Regions > [region] > Physics Conditions > Momentum Source Option node and set Method to one of the following options:
    • Specified—allows you to add a specified momentum source.
    • Fan—applies the effect of a rotating fan to the fluid cells within a region that you select. For further instructions, see Using the Fan Momentum Source.
  2. For a specified momentum source, do the following:
    1. Select the Physics Values > Momentum Source node and specify the momentum source as force per volume. A positive value adds momentum; a negative value removes momentum.
      If you want to specify a momentum source that varies spatially across the region or that depends on iteration or time, you can create a field function, table, or user code library and use it to specify the momentum source.
    2. For a momentum source that is a function of velocity, select the Physics Values > Momentum Source Velocity Derivative node and set the derivative of the momentum source with respect to the x-, y-, [z-] components of velocity as a vector profile value (for a Segregated Flow simulation) or as a tensor profile value (for a Coupled Flow simulation).
      Example: Suppose the following Momentum Source that is a user field function of velocity:

      [C1; C2; C3] * $$Velocity + [C4; C5; C6]

      where C[n] are constants.

      For this momentum source, you specify its Momentum Source Velocity Derivative depending on the selected Flow model as:

      Flow Model Momentum Source Velocity Derivative
      Segregated Flow ( ∂ s u , x ∂ u ∂ s u , y ∂ v ∂ s u , z ∂ w ) = ( C 1 C 2 C 3 ) = [C1; C2; C3]
      Coupled Flow ( ∂ s u , x ∂ u ∂ s u , x ∂ v ∂ s u , x ∂ w ∂ s u , y ∂ u ∂ s u , y ∂ v ∂ s u , y ∂ w ∂ s u , z ∂ u ∂ s u , z ∂ v ∂ s u , z ∂ w ) = ( C 1 0 0 0 C 2 0 0 0 C 3 )

      This tensor can be specified as a Principal Tensor, where the XX Component equals C1, the YY Component equals C2, and the ZZ Component equals C3.

    3. For a Coupled Flow simulation and for a momentum source that is a function of pressure, select the Physics Values > Momentum Source Pressure Derivative node and set the derivative of the momentum source with respect to pressure.
To add a mass source to a region:
  1. Select the Regions > [region] > Physics Conditions > Mass Source Option node and activate Mass Source Option.
  2. Select the Physics Values > Mass Source node and specify the mass source as mass per unit volume per unit time.
    A positive value adds mass; a negative value removes mass. You can use a field function, table, or user code library to describe a dependence on space, iteration, or time.
  3. For a mass source that is a function of pressure, select the Physics Values > Mass Source Pressure Derivative node and set the derivative of the mass source with respect to pressure.
  4. For a Coupled Flow simulation and for a mass source that is a function of velocity, select the Physics Values > Mass Source Velocity Derivative node and set the derivative of the mass source with respect to the x-, y-, [z-] components of velocity as a vector profile value.
NoteSimcenter STAR-CCM+ uses the source derivatives in the linearization of the discrete, non-linear transport equations. You are strongly advised to specify the derivatives in order to improve the stability and convergence rate of the solution.

For more information, see Flow Regions Reference.