Creating a Conformal Mesh

Wherever possible, Simcenter STAR-CCM+ aims to generate a conformal mesh between parts. This section provides advice about how to make sure that a mesh is conformal.

A conformal mesh is a mesh which encompasses separate geometry parts without interrupting the continuity of the mesh between contacting parts. In a conformal mesh, the perimeter of cell faces that are on the surface of one part, match up exactly with the coincident cell faces on a contacting part.

The process of making sure that a mesh is conformal begins with the original geometry parts - long before setting up the meshing procedure. If the CAD or import tessellations of geometry parts are conformal when they are imported to Simcenter STAR-CCM+, the surface remesher in Simcenter STAR-CCM+ maintains this conformality. The quality of the starting geometry affects the quality of the surface mesh, which in turn affects the quality of the volume mesh, and therefore the accuracy of a solution.

The surface remesher in Simcenter STAR-CCM+ aims to generate a conformal surface mesh but does not fix geometries that are non-conformal.

It is important to define the contacts between the surfaces. Simcenter STAR-CCM+ creates strong contacts between part surfaces when geometry is conformal, or weak contacts when geometry is not conformal. See In-Place Contact.

  • If conformal CAD parts are imported with the Import Surface Option Create Part Contacts from Coincident Entities activated, strong contacts are created automatically and appear under the Geometry > Contacts node. The Output window displays the message Created n new Part Contacts from n pairs of coincident faces. - where n is the number of strong contacts that are created.
  • If no part contacts are created, you can imprint parts using an Imprint mesh operation with the option Perform CAD Imprint activated. See Imprint Parts. Make sure that the Geometry > Operations > Imprint node Property Resulting Mesh Type is set to Conformal. Upon executing the Imprint operation, the Output window displays the message Imprint operation Imprint created n new contact(s).
  • You can also find part contacts by right-clicking the Geometry > Contacts node and selecting Find Part/Part Contacts, however, it is not guaranteed that these contacts are strong and can create a conformal mesh.

The contacts must be defined between parts before moving on to meshing. Before creating a volume mesh, assign parts to regions with the option to Create Interfaces From Contacts activated. See Regions Layout Workflow. Conformal interfaces are created from strong contacts and allow you to create a conformal mesh.

Since the meshers treat each type of interface differently, set the Interface Type before creating the mesh. See Interfaces Overview.

When a Periodic interface is set, you can determine if the mesh at the interface is conformal when running the Surface Remesher by checking messages in the Output window, such as:

  • Before the remesher starts:

    Before Orienting Faces outward

    Creating conformal mesh on periodic interface:

    Created conformal mesh for interface Block/Block -> Block Surface 2/Block Surface 4 using translation (0 1 0)

  • Before the volume meshing starts:

    Surface Remesher is up to date

    Creating conformal mesh on periodic interface:

    Created conformal mesh for interface Block/Block -> Block Surface 2/Block Surface 4 using translation (0 1 0)

When using any other type of interface, you can determine if the mesh at the interface is conformal after creating a volume mesh, either:

  • Create an Automated Mesh Operation using the Surface Remesher model along with either the Tetrahedral or Polyhedral core volume mesher. Make sure you deactivate the Automated Mesh Operation property Per-Part Meshing (when activated, the resulting mesh is non-conformal). To make sure that the mesh is conformal, if the upstream mesh operation creates quadrilateral elements at the interface, the downstream mesh operation aims to create a mixed mesh with both pyramidal and tetrahedral cells. If the downstream mesh operation has a tetrahedral mesher with prism layers or advancing layers, the resulting mesh is conformal only if the interface between the operations is set to generate prisms. The Trimmed cell mesher does not create a conformal mesh - regardless of using the prism mesher at the interface or not.
  • Create a Directed Mesh Operation using the option to create a source mesh using an existing mesh. See Creating a Source Mesh Using an Existing Mesh.

Upon completion of volume meshing, you can check if the resulting mesh is conformal by either:

  • Right-clicking the Interfaces > [Interface] node and selecting Initialize.

    The Output window displays a message such as:

    Updating 1 boundary mode interface

    Block/Block 2: 116 intersection faces (conformal match)

  • Visualizing the mesh in the [Mesh Scene] window.

If the geometry is not recognized as conformal, return to the point of geometry creation and fix the geometry then re-import it. Or, after importing to Simcenter STAR-CCM+, you can fix the geometry using the surface repair tools. See The Surface Repair Tool.