Polyhedral Mesher

Polyhedral meshes provide a balanced solution for complex mesh generation problems.

They are relatively easy and efficient to build, requiring no more surface preparation than the equivalent tetrahedral mesh. They also contain approximately five times fewer cells than a tetrahedral mesh for a given starting surface. Multi-region meshes with a conformal mesh interface are allowed.

The polyhedral meshing model utilizes an arbitrary polyhedral cell shape in order to build the core mesh. In Simcenter STAR-CCM+, a special dualization scheme is used to create the polyhedral mesh from an underlying tetrahedral mesh, which is automatically created as part of the process. Simcenter STAR-CCM+ calculates the initial cell count from this underlying tetrahedral mesh. The polyhedral cells that are created typically have an average of 14 cell faces.

The following sequence of images demonstrate the process of generating a polyhedral mesh in Simcenter STAR-CCM+,

A tetrahedral mesh is generated for the input surface.

A dualization scheme is used to mark the center of the tetrahedral cells (red dots in example), as well as the midpoints (blue dots in example) on the boundary edges.

Polyhedral cells are generated, starting from the boundary edges.

Further polyhedral cells are generated from the outer layer.

The process carries on until all polyhedral cells are generated.

An example polyhedral core mesh is shown below using either a Triangular or Quad Dominant surface mesh:

Volume cell sizes grow from the surface to the far field or core mesh (depending on application). The Volume Growth Rate controls how quickly the cell size increases with increasing distance from the surface, and from refinement zones to mesh away from the zones. The Maximum Cell Size control sets the upper limit on how large cells can grow.

You can set custom cell sizes in any part of the domain using volumetric controls in conjunction with a suitably defined part. The part defines the volume within which the custom cell size applies. The Volume Growth Rate governs the rate of transition from the custom cell size to the core mesh.

Field function based refinement can be used to create local density variations which are based on a mesh size table.

When the polyhedral mesher is used with a quadrilateral surface mesh, the quadrilateral topology is preserved on the surface. If you are using a quadrilateral surface mesh with the polyhedral mesher and prism layer mesher, the surface mesh must contain isotropic quadrilateral elements only.

When you use the polyhedral mesher with a periodic interface, the mesher attempts to produce a conformal mesh for the periodic boundary pair. However, if a concave cell is split on one side, the corresponding split is sometimes not made when meshing in parallel. The missing split is made later when the interface is initialized before running the simulation.

For geometries containing cylindrical elements, the polyhedral mesher can be used with the generalized cylinder mesher, which generates extruded orthogonal cells along the length cylindrical sections. For geometries containing thin walled structures, the polyhedral mesher can be used with the embedded thin mesher, which generates prismatic type cells in areas that are considered to be thin.

Polyhedral meshes can normally be generated with free floating baffles. However, issues are sometimes seen when the baffles do not have prismatic layers. If you encounter such issues, activate the prism mesher for the baffles so that at least one layer of prism cells is generated to help alleviate problems with cell generation at baffle edges.

Some meshes generated by a pipeline that includes the polyhedral mesher can show additional edges on the boundary. These additional edges are added by the polyhedral mesher in order to avoid warped boundary faces and to enhance conformality among regions. The effect is stronger if the triangulation of the input surface is coarse.

Polyhedral Mesher Guidelines