Manipulating Regions and Boundaries

Combine the separate mesh blocks into a single contiguous mesh, then rename the mesh entities before continuing with the simulation.

Use the following steps:

  1. In the intake window, open the Regions node.
    See three separate regions, corresponding to the three mesh blocks that were imported.
  2. Click to select each of the region nodes (Fluid_1, Fluid_1 2, and Fluid_1 3) in turn.
    The selected region is highlighted and labeled in the Geometry Scene 1 display.

There are two alternative approaches for combining these regions so that information can propagate between them:
  • Create internal interfaces.
  • Fuse the regions and boundaries.

Using internal interfaces is advantageous if the mesh is to be manipulated further at a later stage, since interfaces can easily be deleted and created. However, there is likely to be some (most likely small) computational overhead that is associated with the interface. In this case, since the mesh does not need to be changed, combine the regions and fuse the adjacent boundaries, creating a single contiguous mesh. The process of “fusing” creates a (possibly non-conformal) interface, and then merges that interface into the mesh.

To combine the separate regions into one, use Shift Click to select all three region nodes.

  1. Right-click and select Combine... .


  2. In the Combine Regions dialog, make sure that all regions under it are selected.


  3. Activate Combine boundaries with similar names.
In many situations, the Fuse adjacent boundaries option can also be used. However, in this case, the specified tolerance is not suitable for all the boundaries to be fused, so complete the fusing operation later.
  1. Click OK to combine the regions without fusing the boundaries.

    As a result of this operation, a single region node remains.



Since there is only one region now, you can simplify the region name.
  1. Rename the Fluid_1 node to Fluid.

Now that the regions have been combined, fuse the adjacent boundaries that are currently separating the regions. The mesh is not conformal at these boundaries, so a non-conformal intersection needs to be computed as part of the fusing process. Essentially, an interface is created and then merged into the mesh.

The intersection process requires the specification of a tolerance. Use a value of 0.02 (default 0.05) and then perform checks to make sure that this is suitable.

Before creating interfaces, the freestream boundary types must be redefined as walls. This allows the solution to be initialized without activating a flow model, normally a requirement of freestream boundaries.

  1. Open the Fluid > Boundaries node.
  2. Select all the freestream boundary nodes: Free_Stream-4, Free_Stream-6, Free_Stream-31 and Free_Stream-32 and set the Type to Wall.


This bypasses the need to activate any models before initializing, the latter being a necessary step for testing the intersecting interface tolerance.
  1. Select the Free_Stream-4 node, then use the Ctrl Click approach to select the Free_Stream-32 node.
    (It is important to select the boundaries in this order.)
  2. Right-click and select Create Interface.
  3. Select the Interfaces > Interface 1 > Physics Values > Intersection node and set Geometric Tolerance to 0.02.
You are now ready to initialize the solution manually.
  1. Click (Initialize Solution) on the toolbar or select Solution > Initialize Solution.
To determine whether the test was successful, inspect boundaries Free_Stream-4 [Interface 1] and Free_Stream-32 [Interface 1] in the Geometry scene.
  1. To gain access to them, first locate the Free_Stream-31 part by clicking its node.
  2. Right-click that part in the scene and select Hide.


  3. Next, select the nodes of the two internal interface boundaries, then click the (Reset View) button on the toolbar to bring them into focus. (Zoom and rotate if necessary.)


The parts appear intact, also showing that the interface was intersected correctly. This shows that the tolerance value of 0.02 is the right one. Delete the interface so that the boundaries can be fused.
  1. Right-click the Interfaces > Interface 1 node and select Delete.
  2. Click Yes in the confirmation dialog.
  3. Select the nodes of the Free_Stream-4 and Free_Stream-32 boundaries (in that order), right-click and select Fuse.


    The sequence of boundary selection can affect the results of the fuse operation. When you fuse boundaries, Simcenter STAR-CCM+ attempts to take the second boundary selected by you and project it onto the first.

Hence, when deciding on the sequence of boundaries to select for fusing, always select the one with the finer mesh grid first. This instructs Simcenter STAR-CCM+ to project the coarser boundary onto the finer one, leading to better results in the mesh grid. If you were to select the boundaries in the opposite order (trying to project the finer boundary onto the coarser one), this may essentially fail, as you may see only parts of the fused boundaries shown in the scene display.
  1. In the Fuse Boundaries dialog, make sure that these boundaries are selected:


  2. Click OK.

    Both these boundaries disappear from the tree, since fusing boundaries incorporates them into the interior mesh grid.

  3. Repeat the fusing process for the Symmetry-1 and Symmetry-7 boundaries. Again, use the default tolerance, 0.02.
  4. Combine (do not fuse) the Free_Stream-31 and Free_Stream-6 boundaries by selecting their nodes, right-clicking, and selecting Combine.
    This creates a single freestream boundary entity.
  5. Select all the remaining symmetry plane nodes, right-click, and select Combine.
  6. Select the Wall-5 node and look in the Geometry scene.
  7. To see the part more clearly, click (Make Scene Transparent).


    This boundary includes two non-contiguous surfaces.

  8. To correct this, right-click the Wall-5 node and select Split Non-Contiguous.


  9. Select the Wall-5 node and then the new Wall-5 2 node separately. The split action has made them into two separate boundaries.


  10. Rename the following nodes:
    NodeNew Name
    Free_Stream-31Free_Stream
    Pressure-2Pressure
    Symmetry-3Symmetry
    Wall-1Cowl
    Wall-2Stbd Wall
    Wall-3Port Wall
    Wall-5Extension_Outer
    Wall-5 2Spinner
    Wall-6Extension_Inner

    This portion of the simulation tree appears as shown below:



  11. Save the simulation.