The Open Source CFD code dolfyn is accompanied by a preprocessor.

The preprocessor writes a geometry file in a format suitable for dolfyn. The input is a set of three files which describe the cells, vertices en the boundaries. Dolfyn reads the geometry file and a separate input file. In this input file the user sets numerical and model data, boundary conditions etc. The input file can be edited with any simple editor.

Launchpad is a software collaboration platform on which the software package is hosted.

Clicking on “browse the code” > “view revisions” > “download tarball” will download the latest version available.


Everything here is still under heavy development. Updates and changes are not ruled out; in matter of fact, expected.

Both codes can be compiled with any modern Fortran95 compiler. Be aware that the current Fortran77 subroutines have to be compiled with the same compiler. The codes were successfully tested using ifort and gfortran on Linux and using gfortran under MinGW on Windows.

Also, gmsh is the advised Finite Element Mesh generator. A separate code is provided to convert gmsh format to dolfyn input files.

Dolfyn writes out in VTK file format, suitable for postprocessors like VisIt.

Lastly, you will need a standard ascii/text editor (e.g. Atom, Notepad++, gedit, Vim).

Test Files

If you wish to take dolfyn for a test run, you can do so by using the files in this demo package:


As can be seen, the preprocessor only needs three simple files:

  • A file with cell definitions (*.cel)
  • A file with the vertices (*.vrt)
  • And the boundaries (*.bnd)

nr, i1, i2, i3, i4, i5, i6, i7, i8, id

With the cell number ‘nr’, and the 8 corner nodes of a hexaeder (i1 t/m i8). Each cell has a pointer to an id in a table. This ‘id’ is reserved for the future (for the time being set it to ‘1’).
The accompanying ‘format statement’ is a ‘free format’ (*).
Cell shapes are defined as:

  • Hexaeder: i1, i2, i3, i4, i5, i6, i7, i8
  • Prism or wedge: i1, i2, i3, i3, i5, i6, i7, i7
  • Pyramid: i1, i2, i3, i4, i5, i5, i5, i5
  • Tetraeder: i1, i2, i3, i3, i5, i5, i5, i5

nr, x, y, z

With the number ‘nr’ and it’s position in 3D (x, y, z).

The accompanying ‘format statement’ is: i9,6x,3g16.9

nr, i1, i2, i3, i4, id

With number ‘nr’ and the 4 corner nodes of a face of a hexaeder (i1 t/m i4). The boundaries point to an ‘id’ which values will be set in the control file (*.din). All boundary faces without an ‘id’ will be given the default id of ‘0’.
The accompanying ‘format statement’ is in ‘free format’ (*). Two variants are defined:

  • Quad: i1, i2, i3, i4
  • Tri: i1, i2, i3, i3


The files are in Portable Document Format (pdf). You can save them and open them with Adobe’s Acrobat Reader, or for example with Ghostview.


You need to know what to do. The codes and files are ‘as is’. The software and files are there to give you an impression only without any guarantee whatsoever.