Nek5000 can handle any complex geometry. However, generating good hexahedral meshes has been a daunting task for engineers and researchers alike.

Mesh File Formats

Meshes can be read in Nek5000 via the .rea file format (described here) or field file format.

Mesh Generators and Converters

Nek5000 is by default equipped with two mesh generators genbox and PRENEK. Additionally 2D meshes can be extruded using n2to3.

Meshes can also be provided by an external software

  • CUBIT can be loaded in Nek via MOAB.  Some short tutorials are provided below:
  • MeshKit has extensions to external libraries, such as CAMAL/triangle/tetgen/netgen, post-hex-mesh-boundary layer generation tool, and a custom tool (RGG) for generating complex reactor core geometries. See also the RGG GUI Users Guide for more info.
  • mshconvert is a Python utility for converting a fluent mesh (.msh) to an .rea file that can be read by Nek5000. It is developed by Mikael Mortensen at University of Oslo. (Thanks to KTH Royal Institute of Technology for the recommendation.)
  • foamToNek is a Python utility for converting OpenFOAM meshes to .rea files that can be read by Nek5000.  It is developed by Haomin Yuan at Argonne National Laboratory.

Any submissions from our users, such as mesh converters etc. are strongly encouraged. (please email Ron Rahaman (, or Oana Marin (