TL;DR
The flow5 project has been declared FOSS and recent updates link the codebase to the Gmsh SDK and refactor modeler and solver components into a library. Several meshing, analysis and UI changes were made across multiple point releases, including format changes to .fl5 files that affect backward compatibility.
What happened
Between late 2023 and January 2026 the flow5 project received a series of updates culminating in a formal FOSS declaration in v7.53 and a subsequent v7.54 change that ties the tool to the Gmsh SDK. The code was refactored to separate modeler and solver classes into a library, and all meshing interfaces were altered to support Gmsh in addition to the built-in mesher. The changelog lists multiple modelling and analysis adjustments: options to build fuselage meshes aligned to wing mid-camber, removal of some panel connections that slightly affect pitching moment, and a switch to an OCC-based evaluator for certain inertia calculations. Several UI, post-processing and analysis fixes were also applied across releases. Notably, the .fl5 project file format was modified in multiple releases, and newly saved files are not readable by older flow5 versions.
Why it matters
- Integration with the Gmsh SDK expands meshing backend options and could affect mesh quality and workflow choices.
- Refactoring core components into a library improves modularity and may ease maintenance or third-party reuse.
- The FOSS declaration (v7.53) can change how users access, modify and distribute the software.
- Repeated .fl5 format changes create migration and compatibility considerations for teams using mixed versions.
- Removal of IGES import/export and other interface changes could require adjustments to CAD workflows.
Key facts
- flow5 was stated to be FOSS in version 7.53 (January 1, 2026).
- Version 7.54 (January 1, 2026) linked flow5 to the Gmsh SDK and refactored modeler and solver classes into a library.
- Meshing interfaces were updated to use both the Gmsh library and the existing custom mesher.
- An option was added to create fuselage meshes conforming to the wings' mid-camber line; some panel connections were removed affecting pitching moment slightly.
- IGES import/export options were removed in v7.54 due to changes in symbol names in the OCC library.
- Inertia evaluation for xfl-type fuselages was changed to use OCC rather than the previous custom evaluator, with slight impacts on evaluations.
- v7.53 changed the default OpenGL context to 4.6 and modified the .fl5 project file format so newly saved files are not readable by older versions.
- Several analysis fixes and feature tweaks were made across releases, including enabling XFoil analyses (v7.53) and fixes to LLT velocity parameters.
- v7.50 listed features that were to become active when flow5 went open-source, such as on‑the‑fly viscous drag calculations and T6 polars.
What to watch next
- Whether features flagged to 'become active when flow5 goes open-source' (for example on‑the‑fly viscous drag using XFoil and T6 polars) are now enabled in practice.
- How users and downstream workflows respond to the removal of IGES import/export and the move to OCC for certain geometry evaluations.
- compatibility and migration efforts prompted by repeated changes to the .fl5 project file format (note: broader community adoption and forking are not confirmed in the source).
Quick glossary
- Gmsh SDK: A software library and toolkit used to generate meshes for numerical simulations; here it is integrated as an optional meshing backend.
- OCC: A geometry/CAD kernel used for modeling and geometric computations; the release notes indicate some evaluations were switched to use OCC.
- XFoil: A computational tool for aerofoil analysis; the notes reference enabling XFoil analyses and on‑the‑fly viscous drag options tied to XFoil.
- AVL: Aerodynamic analysis software referenced in the release notes for control and polar interoperability and comparisons.
- Mesher: A component that subdivides geometry into discrete elements (mesh) used by numerical solvers; flow5 supports a built‑in mesher and now Gmsh.
Reader FAQ
Is flow5 now open source?
The release notes for v7.53 state that flow5 is FOSS.
Will files saved in the latest flow5 work with older versions?
No; the notes warn that newly saved .fl5 files will not be readable by versions older than specific releases (v7.53 and earlier version notes also indicate format changes).
Does flow5 still support IGES import/export?
IGES import and export options were removed in v7.54 due to symbol name changes in the OCC library.
Are the features promised to activate on open-source now enabled?
Not confirmed in the source.
Release Notes flow5 v7.54, January 1st, 2026 General linked flow5 to the Gmsh SDK refactored the code to isolate modeler and solver classes into a library Modelling/Meshing all meshing interfaces…
Sources
- Flow5 released to open source
- feedback and suggestions (#3379) · Issue · gmsh/gmsh
- Gmsh: a three-dimensional finite element mesh generator with …
- Flow Go SDK
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