Hybrid meshes can help in optimizing grids in complex geometries allowing for structured meshes in one part of a geometry, while using unstructured grids in more complex regions.  This tip will show you how to create a simple hybrid (structured/tetrahedral) mesh system in CFD-GEOM V2008.0, as shown in Figure 1.

Figure 1.  Hybrid mesh in CFD-GEOM 

In most hybrid meshes, there will be at least one structured face that will be shared between a structured block and a unstructured domain.  The surfaces that share boundaries with faces from the structured blocks should be created using the edges instead of curves/lines to insure that there will be a proper point-to-point matching.

V2008 allows user to generate hybrid mesh in just 4 simple steps: 

1. Edge Substitution:  To make sure point-point connectivity is maintained between the structured domain and the unstructured domain, substitute edges into the surface where common lines/curves are used (i.e. for both the surface and the face).  In V2008.0, edges can be substituted into surfaces in one operation.  If you would like more information on edge substitution, please refer to the user tip “Edge Substitution/Removal for Surfaces in CFD-GEOM“ for CFD-GEOM.  Once the edges have been substituted into the surface, the edge grid points will be cyan color (Figure 2), indicating they are part of a surface.  Note: You will not need this step if the surfaces have already been created using edges.


Figure 2.  Model after substituting edges into the surface.

2. Create the Shell using the five surfaces and the one face.
3. Create the Unstructured Domain using the Shell.
4. Finally, generate the tetrahedral mesh on the Unstructured Domain using the Tet Meshing tool.

Once mesh generation has completed, your mesh should look like the one shown in Figure 3.

Figure 3.  Final hybrid mesh in CFD-GEOM 

Regards,
Kartik Shah
ESI CFD Support Team