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:

1. Creation of discrete surfaces from lines and CAD surfaces
2. Extracting outlines and critical features
3. Split at outlines and critical features
4. 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