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The Connector, the newsletter for CFD Mesh Generation from Pointwise

New Product Releases - March 2011

Gridgen Version 15.17

Gridgen Version 15.17 is now available for production use. It contains two major new features related to the T-Rex algorithm for hybrid mesh generation. Thin surfaces, wakes and other off-body phenomena now can be resolved and overall cell count can be reduced by as much as 29 percent.

Baffles Provide Off-Body Clustering

T-Rex (anisotropic tetrahedral extrusion) is an automated meshing technique that starts from a triangulated surface mesh and extrudes layers of high aspect ratio tetrahedra that transition to a more uniform mesh away from the body. The addition of T-Rex support for baffles (an existing Gridgen feature for resolving thin geometric surfaces) lets the user insert a triangulated surface mesh into the middle of the volume in the vicinity of a flow feature. T-Rex will extrude layers of tets from the baffle, thereby providing a fine mesh for accurately resolving the flow feature.

The example below shows how baffles can be used with T-Rex to cluster the mesh in the wakes behind the tailplanes of the SUBOFF submarine benchmark geometry. Figure 1 shows the geometry of the submarine and the baffles drawn in yellow. As you can see in Figure 1's inset, the baffles are just unstructured domains added as faces to the interior of the block. The triangles on the baffle domains will be reproduced as cell faces in the final volume mesh. Therefore, you can control the volume mesh clustering via the tri mesh density and the geometric shape of the baffle. In this example, each baffle is planar.

Baffles for the SUBOFF Geometry.

Figure 1: For the SUBOFF submarine benchmark geometry, baffles (yellow) have been created in the wake region behind each of the four tailplanes.

The T-Rex algorithm extrudes layers of tets off the baffles in the same manner as it extrudes tets off the boundary layer regions, like the submarine's hull and tailplanes. Therefore, you have the same types of control of the mesh in the baffle regions as in boundary layer regions, including step size and growth rate for the extrusion. After the volume mesh has been generated with T-Rex, a cut through the volume illustrates the effect of the baffles on the clustering, as shown in Figure 2. By removing the baffles from the image and zooming in a bit more on the mesh, you can see the amount of clustering that can be achieved around the baffles. The black regions aren't voids; they are very densely packed tets.

Baffles in the T-Rex Mesh

Figure 2: T-Rex grows layers of tets off the baffles (yellow) just like it grows them off the body.

T-Rex Mesh Clustering to Baffles

Figure 3: The mesh generated around the baffles provides clustering necessary to resolve the wakes behind the tailplanes.

Further Reductions in Cell Count

An optional post-processing step for the T-Rex algorithm is to combine the extruded tets into prisms, thereby combining three cells into one. One case in which this didn't work previously is across block boundaries. While a T-Rex mesh often is created within a single block that spans from the body to the farfield, sometimes circumstances force you to use a multi-block topology. For example, you may need a block boundary at a certain location in order to be able to sample the computational fluid dynamics (CFD) solution. Or perhaps you need a block boundary to model a porous surface or other material change. Regardless of the reason, multi-block topologies would foil T-Rex's prism recombination - until now. With that restriction lifted, the final cell count in some cases dropped 29.4 percent relative to previous versions of the software.

Other Changes in This Release

The other changes in this release consist of several bug fixes that are described in the Release Notes.

More Information and Downloads

You can read about all the fixes in the Resolved Issues section of the Release Notes: www.pointwise.com/library/relnotes.pdf.

The new release is available for download from our web site: www.pointwise.com/support/dload.shtml.

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