Defining CFD Objects

Using the CFD templates, add the required CFD objects to the project tree.

To represent the Simcenter STAR-CCM+ boundaries, add CFD interfaces to the model map:
  1. In the model map, locate the components of type 'Pipe*' that you want to couple with Simcenter STAR-CCM+.
  2. For each pipe section, replace the default 1D orifices with 1D/3D CFDInterface objects using the following procedure:
    1. Delete the default 1D orifices.


    2. Drag and drop the Components > CFDInterface > def node from the project tree onto the model map, then place it at the original orifice position.
    3. Right-click the CFDInterface on the model map and select Start New Link.
    4. Use the Start New Link tool to join the CFDInterface to the adjacent pipes, making sure that the arrows point in the direction of the flow.


    CFD interfaces serve as 1D/3D switches. When GT-SUITE and Simcenter STAR-CCM+ are uncoupled, GT-SUITE solves the flow in the one-dimensional components. When coupled, the GT-SUITE solver supplies boundary conditions to Simcenter STAR-CCM+ and no longer solves the flow in the one-dimensional components.

To define the characteristics of the 1D/3D interfaces, add CFD connections to the model map. To create a CFD connection:
  1. In the project tree, right-click either the Connections > CFDFlowConn node or the Connections > CFDFlowConnBeta node and select Add Object...
    CFDFlowConnBeta connections allow you to control pressure relaxation and mass continuity at the interface.
  2. Define the properties of the CFD connection as follows:
    Property/Attribute Setting
    CFD Domain Sampling Length Specify the length of the volume-averaging zone, across which Simcenter STAR-CCM+ averages the three-dimensional fields, before sending values to GT-SUITE.

    The specified length is rounded up or down to cover the nearest complete mesh cell.

    Make sure that the sampling volume length covers an area of the simulation where there is one-dimensional flow.

    You can visualize the sampling volumes in Simcenter STAR-CCM+ using the Average Zone Flag field function in a scalar scene. See Preparing the STAR-CCM+ Simulation for Co-Simulation.

    CFD Boundary Cross-section (be precise)

    Specify the cross-section of the coupled Simcenter STAR-CCM+ boundary. Set this option so that the areas of the coupling interface between Simcenter STAR-CCM+ and GT-SUITE match. For a mismatch of more than 5%, Simcenter STAR-CCM+ stops the simulation.

    In general, GT-SUITE allows for pipes with circular or rectangular cross-sections. For cross-sections that do not meet these requirements, you can calculate the area of the coupled boundary in Simcenter STAR-CCM+ using a Sum report of the Area field function.

    Species Map Override def
  3. Define the remaining properties based on the type of connection:
    • For a CFDFlowConn object, set Interface Conditions Imposed by GT at the CFD Boundary to one of the following:
      • To couple with a Simcenter STAR-CCM+ velocity inlet or mass flow inlet, select Flow (velocity or mass flow rate).
      • To couple with a Simcenter STAR-CCM+ pressure outlet, select Pressure.

      This choice determines the fields exchanged during the co-simulation. See Boundary Types and Exchanged Fields.

    • For a CFDFlowConnBeta object, set CFD Interface Condition Imposed by GT to one of the following:
      • To couple with a Simcenter STAR-CCM+ velocity inlet, select Flow (CFD imposes GT pressure): Velocity.
      • To couple with a Simcenter STAR-CCM+ mass flow inlet, select either Flow (CFD imposes GT pressure): Velocity or Flow (CFD imposes GT pressure): Mass Flow Rate.
      • To couple with a Simcenter STAR-CCM+ pressure outlet, select either Pressure (CFD imposes GT velocity) or Pressure (CFD imposes GT mass flow).

      This choice determines the fields exchanged during the co-simulation. For more information, see Boundary Types and Exchanged Fields.

  4. Define any remaining properties as appropriate to your case.
To represent the Simcenter STAR-CCM+ region, add a CFD component to the model map:
  1. In the project tree, right-click the Components > CFDComponent node and select Add Object...
  2. In the Create Object dialog:
    1. Set Object Name to the name of the coupled Simcenter STAR-CCM+ region.
    2. In the Simulation Phases tab, set Engine Cycles or Time Before CFD (or "cfdreload") Started to the number of pre-cycles that GT-SUITE runs independently before coupling with Simcenter STAR-CCM+.
      Pre-cycles improve stability in GT-SUITE, providing more accurate boundary conditions from GT-SUITE and therefore reducing the time to reach a converged solution.
  3. Complete the set up by defining the GT-SUITE species. See Defining a CFD Species Map in GT-SUITE.