Setting up the Mesh

The default mesh settings are based on best practices to ensure a high level of accuracy in the solution with a minimum cell count.

For that reason, in most cases, you can maintain the default settings. However, if you encounter convergence problems due to insufficient mesh resolution or if you want to increase the accuracy, you can edit the mesh settings.

To edit the mesh settings:
  1. Right-click the Mesh node and select Edit Mesh Settings.
    The warning triangle () on the Mesh node indicates that you must still generate the mesh (after defining the settings and any custom controls).
  2. In the Edit tab, define the following global mesh and boundary layer settings to suit your requirements:
    • Number of Layers (only for cylinder sector models)
    • Base Size
    • Minimum Size
    • Sharp Edge Angle (deg)
    • Prism Layer
    See Mesh Reference.
    For example, decreasing the Base Size decreases the target cell size in the core of the cylinder, which increases the mesh resolution and with it the accuracy of the solution. However, this increase in the accuracy of the solution also comes with an increase of computational cost.
  3. To commit changes to the default mesh settings, click Apply.

To aid solution convergence, Simcenter STAR-CCM+ In-cylinder automatically extends the volume mesh with orthogonal extruded cells at inlet and outlet boundaries.

NoteMesh extrusion is only supported for planar inlet and outlet boundaries—curved boundaries are not supported.

To edit the extrusion parameters:

  1. In the Extrusion group-box set the following properties:
    • Thickness
    • Number of Layers
    See Mesh Reference—Extrusion.
  2. If you want to disable the mesh extrusion, set Extrude I/O Boundaries to Off.
  3. Click Apply.
During the running simulation, Simcenter STAR-CCM+ In-cylinder re-meshes the geometry based on certain re-mesh criteria to ensure a good cell quality for all crank angles. These re-mesh criteria are also based on best practices and are suitable in most cases. However, you can change the criteria if you wish.

To edit the re-mesh criteria:

  1. In the Re-mesh Criteria group-box, set the following properties:
    • Base Criteria (any one can be satisfied)
      • Min Cell Quality
      • Max Piston Stretching
      • Max Valve Stretching
      • Max Valve Displacement
      • Piston Tolerance
      • Min Cell Quality Reference: This property displays the minimum cell quality after the last re-mesh. DO NOT modify this value.
    • Cell Skewness Criteria (both must be satisfied)
      • Max Cell Skewness Angle 1
      • Min Cell Aspect Ratio 1
    • Bad Morphed Cell Criteria (all must be satisfied)
      • Max Cell Skewness Angle 2
      • Min Cell Aspect Ratio 2
      • Min Cell Quality 2
      • Min Volume Change
      • Min Least Square Quality
    • Valid Face Criteria (both must be satisfied)
      • Max Cell Skewness Angle 3
      • Min Face Validity
    See Mesh Reference—Re-mesh Criteria.
  2. Click Apply, then Close.
  3. If you want to customize the mesh on specific faces of the Engine Part Surfaces Cylinder > Default : Gases or Intake/Exhaust Valve [n] > Default : Solids, first separate those faces into their own Engine Part Surface. See Splitting an Engine Part Surface.
  4. To set customized mesh settings on a specific Engine Part Surface:
    1. Right-click the Mesh > Custom Controls node and select New > Surface Control.
    2. In the Edit dialog, set Surfaces to the respective Engine Part Surface and change the mesh settings as required. See Mesh Reference—Surface Control.
    3. Click Apply, then Close.
Simcenter STAR-CCM+ In-cylinder defines static, dynamic, and temporary mesh refinement zones to ensure a good mesh quality for all crank angle positions. For the temporary mesh refinement zones, which encapsulate the valve curtain interfaces, you can modify the criterion that activates the zones and the thickness of the prism layers within the zones.
  1. Right-click the Parameters node and select Edit.
  2. In the Edit dialog, set the following properties:
    • VCI LCT Enable Value—by default, the refinement zones become active when the valve lift of the respective valves is less than 5 times the closure tolerance. The VCI LCT Enable Value specifies this multiplication factor.
    • VCI Prism Layer Thickness—the thickness of the prism layers within the zones relative to the Base Size.
  3. Click Close.
You can create additional mesh refinement zones to accurately capture flow phenomena in specific areas of the engine. However, in contrast to the predefined mesh refinement zones, Volumetric Controls that you create can not move with the valves or the piston.
  1. If you want to customize the mesh within an additional volumetric zone, define a geometry that encloses the zone of interest and set up a Volume Control:
    1. Create an arbitrary three-dimensional volume shape. See Creating Geometries.
    2. Right-click the Mesh > Custom Controls node and select New > Volume Control.
    3. In the Edit dialog, set Parts to the created Construction Geometry and change the mesh settings as required. See Mesh Reference—Volume Control.
    4. Click Apply and Close.
Simcenter STAR-CCM+ In-cylinder automatically generates the mesh as part of the simulation run. However, if you want to generate and check the mesh before running the simulation, you can do so.

To generate the mesh manually:

  1. In the Mesh Generation toolbar (see Toolbar Reference), click (Generate Volume Mesh)
    The progress of the mesh generation is displayed in the Output window. Once the progress is complete, the warning triangle on the Mesh icon disappears.
    NoteWhen you change mesh settings after the meshing progress is complete, the warning triangle indicates that the mesh is no longer up to date and requires re-execution.