Computational Fluid Dynamics

CFD may be the field where open source is strongest. The solvers here are used in aerospace, automotive and energy alongside commercial packages, and in some cases they are preferable — because you can modify the solver itself when the problem falls outside the standard.

The price is a steep learning curve. There is no wizard leading you through: you define the case in text files or a script, build the mesh in a separate tool, and post-process in a third. Anyone arriving from a commercial package will feel, at first, that they have lost their hands.

If you are starting out, two sensible routes: a cloud platform that runs CFD in the browser with a graphical interface, or beginning with a very simple case in an open solver and following the official tutorial step by step.