March 13, 2020
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.
Ansys Meshing – Sizing
By default, Use Adaptive Sizing is set to Yes, unless Physics Preference is set to CFD or Nonlinear Mechanical (in which case the default is Capture Curvature set to Yes),
Ansys Meshing – Refinement
Refinement controls specify the maximum number of times you want an initial mesh to be refined.
Ansys Meshing – Bias Factor
Source: Ansys Bias Type and Bias Option For edges only, use Bias Type to adjust the spacing ratio of nodes on an edge. This feature is useful for any engineering problem where nodes need to be clustered on an edge or group of edges, or if there is a need to bias the...
Ansys Meshing – Hexahedral Mesh
The MultiZone mesh method provides automatic decomposition of geometry into mapped (structured/sweepable) regions and free (unstructured) regions. It automatically generates a pure hexahedral mesh where possible and then fills the more difficult to capture regions with unstructured mesh.
Ansys Meshing – Sizing (SOFT / HARD)
If your sizing controls are scoped to either the source or target face, the mesher will transfer the size control to the opposite face. If you have a size control on both faces, the size on one of the faces will be used. That face is automatically determined by the software.
Ansys Meshing – Local Sizing
The Sizing options provide greater control over the following properties:
Mesh growth (transition) between small and large sizes based on a specified growth rate
Ansys Meshing – Multizone + Inflation
The MultiZone mesh method provides automatic decomposition of geometry into mapped (sweepable) regions and free regions. When the MultiZone mesh method is selected, all regions are meshed with a pure hexahedral mesh if possible.
Ansys Meshing – Inflation
ou can set the Use Automatic Inflation control so that inflation boundaries are selected automatically depending on whether or not they are members of Named Selections groups.
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