Ansys Meshing – Mesh Types (Hexa, Prism, Polyhedral)

Written by cfd.ninja

March 13, 2020

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Source: Ansys

 When geometries are complex or the range of length scales of the flow is large, a triangular/tetrahedral mesh can be created with far fewer cells than the equivalent mesh consisting of quadrilateral/hexahedral elements. This is because a triangular/tetrahedral mesh allows clustering of cells in selected regions of the flow domain. Structured quadrilateral/hexahedral meshes will generally force cells to be placed in regions where they are not needed. Unstructured quadrilateral/hexahedral meshes offer many of the advantages of triangular/tetrahedral meshes for moderately-complex geometries.

A characteristic of quadrilateral/hexahedral elements that might make them more economical in some situations is that they permit a much larger aspect ratio than triangular/tetrahedral cells. A large aspect ratio in a triangular/tetrahedral cell will invariably affect the skewness of the cell, which is undesirable as it may impede accuracy and convergence. Therefore, if you have a relatively simple geometry in which the flow conforms well to the shape of the geometry, such as a long thin duct, use a mesh of high-aspect-ratio quadrilateral/hexahedral cells. The mesh is likely to have far fewer cells than if you use triangular/tetrahedral cells.

Converting the entire domain of your (tetrahedral) mesh to a polyhedral mesh will result in a lower cell count than your original mesh. Although the result is a coarser mesh, convergence will generally be faster, possibly saving you some computational expense.

In summary, the following practices are generally recommended:

  • For simple geometries, use quadrilateral/hexahedral meshes.
  • For moderately complex geometries, use unstructured quadrilateral/hexahedral meshes.
  • For relatively complex geometries, use triangular/tetrahedral meshes with prism layers.
  • For extremely complex geometries, use pure triangular/tetrahedral meshes.

In this tutorial we show the results of a heat transfer simulation using different types of meshes (Tetrahedral mesh vs Hex/Prism vs Polyhedral mesh). You will notice the differences between the number of elements and the results and the computational time. 

Tutorial: CutCell using Ansys Meshing.

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