6.3.7 NASTRAN Files

There are three different ways in which you can import a NASTRAN file into ANSYS FLUENT:

• You can generate a NASTRAN surface or volume mesh containing triangular, quadrilateral, tetrahedral, wedge, and/or hexahedral elements, and import it into TGrid using the commands described in the TGrid User's Guide and adhering to the restrictions described in Appendix B of the TGrid User's Guide. In TGrid, complete the mesh generation (if necessary) and then follow the instructions in Section  6.3.3.

• You can generate a NASTRAN volume mesh with linear triangular, quadrilateral, tetrahedral, wedge, or hexahedral elements, and import it directly using the File/Import/NASTRAN menu item, as described in Section  4.12.13.

• You can generate a NASTRAN volume mesh with linear triangular, quadrilateral, tetrahedral, wedge, or hexahedral elements. Then use the fe2ram filter to convert the NASTRAN file to the format used by ANSYS FLUENT. To convert an input file in NASTRAN format to an output file in ANSYS FLUENT format, follow the instructions below in Section  6.3.11. After the output file has been written, you can read it into ANSYS FLUENT using the File/Read/Mesh... menu item, as described in Section  4.2.

After reading a triangular or tetrahedral NASTRAN volume mesh using the latter methods perform smoothing and swapping (as described in Section  27.13) to improve its quality.

Recognized NASTRAN Bulk Data Entries

The following NASTRAN file datasets are recognized by the ANSYS FLUENT mesh import utility:

• GRID single-precision node coordinates

• GRID* double-precision node coordinates

• CBAR line elements

• CTETRA, CTRIA3 tetrahedral and triangular elements

• CHEXA, CQUAD4, CPENTA hexahedral, quadrilateral, and wedge elements

For 2D volume meshes, the elements must exist in a constant $z$ plane.

Deleting Duplicate Nodes

NASTRAN may generate duplicate or coincident nodes in the process of creating elements. These nodes must be removed in NASTRAN before writing the file for import into ANSYS FLUENT.