By allowing you to combine different mesh types in a single CFD model, hybrid meshes allow you to get the optimal balance between solution accuracy and mesh generation efficiency. TGrid 3.0, in the final stages of prerelease testing, will bring powerful hybrid mesh generation tools into the hands of Fluent users in an efficient and convenient environment.

Efficient Model Building

Figure 1 shows a hybrid mesh generated for a conical filter. The mesh contains regions of hexahedral and tetrahedral cells that have been joined by layers of pyramids. To build this zonal hybrid mesh, the hexahedral mesh region and the triangular surface mesh on the remainder of the geometry were brought into TGrid. In TGrid, a layer of pyramids was added to the quadrilateral faces where appropriate. Finally, a tetrahedral volume mesh was automatically generated for the remainder of the model. Zonal hybrid meshes like this can combine the best characteristics of different cell types, using hexahedral cells in regions of the geometry that are easily meshed and tetrahedral cells in regions that are more geometrically complex.

TGrid 3.0 is also capable of generating nonconformal hybrid meshes, taking full advantage of the nonconformal interface capability in the upcoming 4.2 releases of FLUENT/UNS and RAMPANT.

Figure 1: Zonal hybrid mesh on a conical filter. Local mesh types can be selected to maximize mesh quality and minimize mesh generation time.

Viscous Hybrid Meshes for Near-Wall Accuracy

Figure 2 demonstrates a second class of hybrid meshes that TGrid 3.0 can create: viscous hybrid meshes. These meshes include layers of high-aspect-ratio prisms extruded from triangulated surfaces, with tetrahedral cells outside the layered mesh. To generate the mesh on the passenger car in Figure 2, a triangular surface mesh was generated in GeoMesh and read into TGrid 3.0. Triangular prisms were then grown away from the surface mesh for accurate resolution in the boundary layer. TGrid 3.0 automatically retriangulated the adjacent symmetry plane, after which the remaining volume was automatically filled with tetrahedra.

Prismatic layers can be grown from triangular, quadrilateral, and mixed surface meshes. Several methods are available for controlling growth rates. Layers can be extruded along specified vectors or grown using an advancing front algorithm that attempts to preserve mesh quality as the layers grow away from irregular surfaces.

Figure 2: Viscous hybrid mesh on an automotive exterior. Prisms provide an efficient high-quality mesh around the vehicle surface, while you retain the ease of triangular surface meshing.

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