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Nov/Dec 2013
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The Connector, the newsletter for CFD Mesh Generation from Pointwise

November / December 2013

Pointwise Meshing – What's New and What's Coming

Pointwise Version 17.1 R4

Many of you have already had an opportunity to delve into the new capabilities in V17.1 R4 (released on 30 September), either through your own exploration and usage or via the webinar we held on 07 November.

Those of you who have not yet had chance to install and exercise V17.1 R4 will be interested to learn about everything awaiting you.

New and Updated CAE Solver Interfaces

The DLR TAU Code (tau.dlr.de) is now a supported computational fluid dynamics (CFD) solver. TAU is primarily used for aircraft configurations from subsonic to hypersonic flow regimes using hybrid unstructured meshes and an efficient parallel solver.

The existing native interface to OpenFOAM® has been upgraded with the addition of support for Sets and Zones. Three main reasons for using Sets and Zones with OpenFOAM are:

  1. When running multiple reference frame calculations for rotating machinery applications, the flux equation requires solution for an extra term. Therefore, rotating faces and cells must be collected and stored in face/cell Zones.
  2. For multiphase calculations, Sets and Zones are necessary to track the physical properties of the different phases.
  3. Sets and Zones can be used for post-processing purposes.

Collections of faces and cells are defined with the CAE, Set Volume Conditions command (Figure 1). How faceSets, faceZones, cellSets, and cellZones are exported is defined in the CAE, Set Solver Attributes command (Figure 2).

OpenFOAM Sets and Zones in the Set VC panel

Figure 1: Setting cell sets and zones for OpenFOAM is done in the Set Volume Conditions command. +

exporting OpenFOAM Sets and Zones

Figure 2: How cells and zones are exported is defined in the Solver Attributes command. +

Finally, the existing CAE interface to the FDNS/UNIC solver was rewritten using Pointwise's recently-added plugin API for face-based mesh data.

Refined Grid Methods

Two improvements were made to the elliptic PDE technique for smoothing structured volume grids.

The option to compute spacing and angle constraints using data from an adjacent grid for face-based control functions has been added to the elliptic PDE technique for smoothing structured volume grids (Figure 3). This method of computation used to be available only for surface grid smoothing.

adjacent grid spacing and angle constraints for blocks

Figure 3: Spacing and angle constraints for blocks can now be computed using information from an adjacent grid. +

Also in the elliptic PDE technique for volume grids, we improved the manner in which a face with a floating boundary condition interacts with a non-floating face on which orthogonality has been specified. Now the orthogonality condition has a much stronger influence on the shape of the floating face so that it also emanates orthogonally from the non-floating face.

Users of the T-Rex (anisotropic tetrahedral extrusion) technique for hybrid meshing will appreciate how recombination of near-wall tets into prisms has been improved for “chains” of blocks – a blocking topology where several T-Rex volume meshes are stacked end-to-end. Instead of having to use a multi-pass process involving initialization of each individual block and than a final initialization of all blocks at once, a new multi-block recombination algorithm has been implemented that handles this in a single pass, greatly simplifying the workload.

Improved Performance

Significant improvements in code performance were made to three commands.

  • If the initial extrusion front for a T-Rex mesh consisted of thousands of domains, it could take more than an hour for it to initialize. Refactoring the code that assembled the initial front reduced that time to less than five minutes.
  • In another case of speeding up solver initialization, the time required to set up the elliptic PDE solver for structured surface grids was sped up by a factor of 10.
  • Visualizing the volume ratio metric in the Examine command for multiple grids is now 750 times faster than previous versions.

Usability and Workflow Enhancements

Formerly, control points had to be deleted one at a time in Edit, Curve. This command has been updated so you can easily delete multiple control points up to and including all interior control points (Figure 4).

deleting multiple control points

Figure 4: Multiple control points can now easily be deleted in Edit, Curve. +

Finally, Pointwise is now compatible with the GridPro structured grid generation software from Program Development Co. Structured and unstructured domains can be exported from Pointwise to native GridPro formats for use as a faceted geometry definition. GridPro's volume grid format can be imported by Pointwise. This native format data exchange allows a workflow like the following:

  1. Pointwise
    1. Import CAD file.
    2. Generate surface meshes.
    3. Export surface meshes to GridPro.
  2. GridPro
    1. Import surface meshes as geometry.
    2. Generated multi-block structured grid around the geometry.
    3. Export volume grid file.
  3. Pointwise
    1. Import volume grid file.
    2. Add other blocks, including unstructured and hybrid meshes.
    3. Export entire grid to flow solver.

Pointwise V17.2 – What's In-Work

The next major release of Pointwise will be V17.2 and at the time of this writing there are new features at various stages in our development pipeline. (Please read the important note at the end of the article.)

Let's first consider the completed features and have been fully tested:

  • FUN3D (fun3d.larc.nasa.gov) is now supported with a native interface.
  • A native interface to the Gambit Neutral file has been added.
  • Support for NASTRAN files has been updated by exporting true pyramid elements (instead of degenerate prisms).
  • The STAR-CD native interface has been updated by rewriting it using the face-based plugin API.

These next features are complete from a development standpoint but not from a testing standpoint:

the new toolbar implementation of Draw Curves

Figure 5: Draw Curves on the toolbar has been changed to a drop down menu. Your last selection becomes the default.

  • The Draw Curves button on the toolbar has been modified to be a dropdown menu, allowing you to either select the default curve type and begin drawing or choose another curve type which then becomes the default (Figure 5).
  • Mirror during export provides the ability to export a full grid to a CAE file when you have only created a half-symmetry grid. Imagine using this to generate half an aircraft mesh and then mirroring it on export to perform yaw studies, for example.
  • The quality of shaded surface display has been improved through the use of OpenGL shaders (on supported hardware). This work also involved several performance improvements to the graphics. Also, a user-positionable light source has been added (Figure 6).
user positionable light source

Figure 6: With the new light source control, you can view objects from the shaded side as shown above. +

Several features are either still in development or development is just now beginning. This includes upgrading our CGNS support to v3 including the ability to export a file containing both structured and unstructured zones, a new assembly technique for complex volume grid topologies that will automatically assemble baffles and internal voids, and expanding our Linux support to include Ubuntu, Open SUSE, and CentOS.

Finally, the two marquee features planned for V17.2 will have a significant impact. However, there's a little bit more development to be completed and then a lot of testing.

Structured domains can now be used as true match boundary conditions for T-Rex. On export, with recombination enabled, the exposed quad faces of the recombined prisms from the viscous unstructured extrusion match the quad faces of the structured domain. Beyond the extrusion, pyramids are used to transition from the quad faces of the domain to tets in the unstructured block.

hex extrusion in T-Rex

Figure 7: This anisotropic hex extrusion from a notional missile geometry was generated using T-Rex. Image created in EnSight. +

And the pièce de résistance – hex extrusion using T-Rex is being developed (Figure 7). As you know, the current T-Rex implementation starts from a tri mesh and extrudes layers of high aspect ratio tets that are post-processed into stacks of prisms. This upcoming major update to T-Rex will allow extrusion to start from a quad mesh and post-process the cells into stacks of hexes. All other attributes of the T-Rex technique will apply to this new scenario.

Your Next Steps

  1. Download and install Pointwise Version 17.1 R4 from www.pointwise.com/download.
  2. Get an introduction to V17.1 R4 by watching the archived webinar at www.pointwise.com/webinar/v171r4.
  3. Keep submitting ideas for new features to your support engineer or email them to pointwise@pointwise.com.

IMPORTANT NOTE: This article contains information that a publicly traded company might categorize as “forward looking statements.” We'll just say that the features described for V17.2 represent a snapshot of our current development pipeline. We cannot guarantee at this time when they'll be completed and released for production use. We will do our best to release them as soon as possible.

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