Mesh: Refining the Mesh

Customize and refine specific areas of the simulation domain using custom controls.

Custom controls override the default controls for the areas that you specify. For example, you can customize the number of prism layers that are generated on a surface that is specified within a custom control. The number of prism layers that are generated outside the custom control match the settings in the default controls.

Local meshing speeds up the re-execution of the surface remesher after local changes are made to the input geometry or mesh settings. With this feature, Simcenter STAR-CCM+ only remeshes surfaces within a defined location and leaves other surfaces unchanged. With local meshing, you set limits on where you want remeshing to occur by defining local extents. In this tutorial, the area surround the fan contains all the changes and refinements to the mesh, so it would be ideal to use a volume extent that encloses the fan.

Create custom controls that focus on specific areas of the simulation domain:

  1. Launch Simcenter STAR-CCM+ and load foundationTutorial_10.sim.

    You can either use the sim file that you saved from the previous tutorial, or load the sim file provided in the tutorials bundle. See Downloading the Tutorial Files from the Support Center Portal.

  2. Save the simulation as foundationTutorial_11.sim.
  3. If the scene showing the fan and enclosure is not open, double-click the Scenes > Fan and Enclosure node.
  4. Adjust the prism layer settings to improve the quality of the prism layer cells around the fan blades and in the small gap between the base of the fan and the enclosure:
    1. Expand the Geometry > Operations > Automated Mesh > Default Controls node.
    2. Select the Prism Layer Controls node.
    3. Set Gap Fill Percentage to 45.
      The gap fill percentage specifies the percentage of space between a narrow gap that the prism layer mesher fills with prism cells.
    4. Set Boundary March Angle to 25.
      The boundary march angle controls the way the prism layers are projected on a boundary that does not have a prism layer.
    5. Set Number of Prism Layers to 3.
    6. Right-click the Automated Mesh node and select Execute.
  5. Set up local meshing:
    The changes made in the previous step improve the prism layers, however further refinement is still required in the rotating region. Local meshing limits the changes to the specified extent, reducing the total time it takes to generate the surface mesh. Areas outside the extent remain unchanged.
    1. Select the Operations > Automated Mesh node and activate the Perform Local Meshing option.
      The Local Extents node is added to the Automated Mesh operation node and a pin is added to the icon of the Automated Mesh operation.
    2. Right-click the Automated Mesh > Local Extents node and select New > Volume Extent.
      A Volume Extent node is added to the Local Extents node.
    3. Select the Local Extents > Volume Extent node.
    4. Set Parts to Disc.
    5. Set Inflation Distance to 2 mm.
      The inflation distance specifies a distance beyond the extent. Any surfaces falling within this distance are included in remeshing, regardless of whether they are connected to the original surface parts covered by the extent.
    6. Set Inflation Layers to 3.
      The inflation layer specifies a number of adjacent bands of triangles by which the extent can grow.
  6. Create a custom control that disables the generation of prism layers on the interface between the static region and the rotating region:
    Prism layers are not required at this location so you can disable them to reduce the cell count in the mesh.
    1. Right-click Automated Mesh > Custom Controls and select New > Surface Control.
      A surface control node, Surface Control, is added to the Custom Controls node.
    2. Rename Surface Control to Disable Prism Layer.
    3. Select the Disable Prism Layer node and click (Custom Editor) next to Part Surfaces.
    4. In the Disable Prism Layer - Part Surfaces dialog, select the Rotating Region > Surfaces > Interface and Static Region > Disc > Interface nodes and click OK.
    5. Expand the Disable Prism Layer > Controls node.
    6. Select the Prism Layers node and set Prism Layers to Disable.
  7. Create a custom control that refines the cell size in the rotating region and customizes the prism layer around the fan blades:
    The rotating graphics card fan contains narrow gaps and would benefit from a finer mesh to capture the flow in and around the fan more accurately. The prism layer is especially important around the fan blades, where the swirling flow is generated. The current prism layer is too thick to resolve the boundary layer accurately, and the prism layer cells are too large. To improve the mesh, decrease the prism layer total thickness.
    1. Right-click Automated Mesh > Custom Controls and select New > Volumetric Control.
      A volumetric control node, Volumetric Control, is added to the Custom Controls node.
    2. Rename Volumetric Control to Fan Cell Refinement.
    3. Select the Fan Cell Refinement node and click (Custom Editor) next to Parts.
    4. In the Fan Cell Refinement - Parts dialog, select the Disc node and click OK.
    5. Edit the Fan Cell Refinement > Controls node and set the following parameters:
      Node Property Setting
      Surface Remesher Customize Size Activated
      Prism Layer Mesher Customize Total Thickness Activated
      Polyhedral Mesher Customize Polyhedral Mesher Activated
    6. Edit the Fan Cell Refinement > Values node and set the following parameters:
      Node Property Setting
      Custom Size Size Type Absolute
      Absolute Size 1.5 mm
      Custom Prism Values > Prism Layer Total Thickness Size Type Absolute
      Absolute Size 0.7 mm
  8. Save the simulation.
  9. To update the volume mesh with the changes, right-click the Automated Mesh node and select Execute.
    The mesh generation takes less time as only the surface mesh inside the extent are regenerated. Surfaces outside the extent remain unchanged and do not mesh. If you want to modify an area outside the extent, either add another extent to cover this area or if more general changes are required, disable local meshing.
  10. To update the surface and volume extruder, right-click the Operations node and select Execute All.
Use the mesh metric plots and scene that you set up in Foundation Tutorial 9 to check how the changes have affected the mesh quality.
  1. View the mesh quality scenes:
    1. If the mesh quality scenes are not displayed in the graphics view, expand the Scenes > Mesh View Scenes node and double-click each scene node.
    2. Select the Mesh View: XY tab in the window.


      The refined cells inside the rotating region are clearly visible. The prism layer thickness inside the rotating region shrinks to fit inside the tight spaces. The prism layer is no longer collapsed in the small gap below the fan.

    3. Select the Mesh View: XZ tab in the window.


      The refined cells inside the rotating region are clearly visible. The prism layer is no longer generated between the two regions. The prism layer is no longer collapsed at the tips of the fan blades.