ESI Group CFD Portal - Exporting STL Files From CFD-GEOM

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Exporting STL Files From CFD-GEOM

A CFD simulation process starts from an accurate representation of the boundaries that usually originates directly from CAD systems. STL and IGES are two of the most common output formats used as a starting point for mesh generation. STL (StereoLithography) files represent 3D surface geometries using a triangular mesh allowing unambiguous transfer of files from one system to another. Each patch in a STL file is defined by three points and an orientation vector.

CFD-GEOM, an integrated geometry modeling and grid generation tool, supports the export of geometries and meshes in several different output formats. Traditionally,CFD-GEOM users have been able to write out ASCII STL files with consistent orientation from triangulated surface meshes. From V2008.2, CFD-GEOM also allows export of quad surface meshes (generated as structured or unstructured) into STL files. Quad facets are automatically split into triangles as per STL requirements. For structured meshes, only 2D blocks (not faces) can be exported.

Figure 1. 'Save STL files' option from File menu

These files can be opened later in any tool supporting STL files such as CFD-VisCART and CFD-VIEW for mesh generation or visualization purposes.

Figure 2. Examples of exported STLs from triangular and quad surface meshes

The exported STL files can also be imported into CFD-GEOM as a discrete surface for further manipulations. A newly implemented discrete modeling engine in CFD-GEOM can import and manipulate meshed surfaces from several external grid formats. Some of the available tools include:

Creation of discrete surfaces from lines and CAD surfaces
Extracting outlines and critical features
Split at outlines and critical features
Boolean operations on closed surfaces

Figure 3. Discrete surface operations showing union of different closed surfaces,
intersection with a plane, and splitting using outlines and critical features.

In future releases, CFD-GEOM users could expect more powerful features including re-meshing of imported discrete surfaces and tet mesh generation from re-meshed discrete surfaces.

If you have any questions about this feature or would like us to discuss some other topic in the future, please let us know.

Regards,
Abraham Meganathan
ESI CFD Support Team

Handling Multiple holes for surface operations in CFD-GEOM

In the past, cutting or filling holes in surfaces with CFD-GEOM required a two step process; 1) pick the surface 2) pick the closed set of curves that forms the hole. Not a bad process but in the case of having to cut the surface with multiple holes, it was quite inefficient since you could only cut one hole at a time.

Scripting and Journaling in CFD-GEOM V2007.2

In CFD-GEOM V2007.2, scripting and journaling are now available. Several improvements have been made to scripting, such as fewer modules that are arranged in a more logical manner, more robust functionality, etc. As in previous versions of CFD-GEOM, the Python scripting language is still used to create the CFD-GEOM scripting functions. If you are interested in scripting and journaling in CFD-GEOM, please read on.

BC/VC Editor in CFD-GEOM

The BC/VC editor allows you to set the problem type as well as Boundary and Volume conditions name and type.

Using Parameters to Create Your Geometry in CFD-GEOM

Often, you need run several different cases where you need to modify one or more geometrical values where the overall shape of the entity is the same, only the size changes. In this case, it is useful to use CFD-GEOM scripting for your grid generation, rather than doing it interactively using the GUI.

Mixing Structured and Unstructured 2D Grids

One of the most common questions that occurs during CFD-GEOM Training sessions is "How do I generate mixed structured and unstructured grids?" Both grid types have their specific advantages and disadvantages, e.g. structured grids are very efficient in resolving the viscous terms, whereas unstructured grids can be used to handle complex geometries.