TL;DR
The flow5 project has been released as free and open-source software (declared in v7.53) and the most recent v7.54 ties the codebase to the Gmsh SDK while reorganizing solver and modeler code into a library. Several meshing and analysis interfaces were altered, some import/export options removed, and backward-incompatible project file changes were reiterated.
What happened
Across a sequence of late-2025 and early-2026 updates the developers of flow5 prepared the aerodynamic analysis tool for public-source release and updated core internals. In v7.53 (Jan 1, 2026) the project is declared FOSS and the release notes warn that newly saved .fl5 project files are not readable by older releases. The follow-up v7.54 (also dated Jan 1, 2026) links flow5 to the Gmsh SDK and refactors the code to separate modeler and solver classes into a reusable library. Meshing interfaces were rewritten to support Gmsh in addition to the original custom mesher, and a new option builds fuselage meshes conforming to wing mid-camber lines. The update also removes some panel connections (between flaps, fuselage and wing) with small effects on pitching moment, drops IGES import/export citing OCC symbol changes, and switches inertia evaluation for xfl-type fuselages to an OCC-based method. Minor analysis fixes, UI tweaks, post-processing corrections and broad code cleanup are also included.
Why it matters
- Open-source status (v7.53) lets users inspect, modify and redistribute the code under FOSS terms.
- Integration with Gmsh brings a widely used external meshing library, potentially improving mesh generation and interoperability.
- The refactor into a modeler/solver library could make the code easier to embed, test or extend by third parties.
- Project-file format changes and removed IGES support can disrupt existing workflows and require migration steps.
Key facts
- flow5 was declared FOSS in version 7.53 (release notes dated January 1, 2026).
- Version 7.54 (January 1, 2026) links flow5 to the Gmsh SDK and refactors modeler and solver classes into a library.
- Meshing interfaces were rewritten to use either the built-in mesher or the Gmsh library.
- A new option was added to construct fuselage meshes that conform to the wing's mid-camber line.
- Panel connections at flap edges and between fuselage and wings were removed; the notes report a slight impact on pitching moment.
- IGES import and export options were removed in v7.54 because symbol names changed in the OCC library.
- Inertia evaluation for xfl-type fuselages now uses OCC rather than the prior custom evaluator, with a slight effect on computed values.
- v7.53 and earlier releases warn that newly saved .fl5 files are not readable by older versions, indicating backward incompatibility of project files.
- Several analysis and UI fixes were applied in v7.54, including LLT velocity parameter fixes, an option to force hinge-location transitions in some calculations, and minor 3D LLT display corrections.
What to watch next
- Whether features that were previously flagged to 'become active when flow5 goes open-source' (for example, some viscous-on-the-fly analyses noted in earlier release notes) are now enabled: not confirmed in the source.
- Community adoption, forks and third-party contributions following the FOSS declaration: not confirmed in the source.
- Practical impacts of removed IGES support and the incompatible .fl5 file format on users' existing projects and toolchains.
Quick glossary
- Gmsh: An open-source 3D finite element mesh generator commonly used to create structured and unstructured meshes for simulation tools.
- OCC: A CAD kernel (Open CASCADE) used for geometry operations, CAD import/export and some geometric evaluations in engineering software.
- IGES: An older neutral file format for exchanging CAD geometry between different systems; support may be removed or limited in modern toolchains.
- XFoil: A software tool for airfoil analysis that is often used to compute viscous aerodynamic characteristics for foil sections.
- AVL: A software tool for aerodynamic and flight-dynamic analysis using vortex-lattice methods; often referenced for compatibility and benchmarking.
Reader FAQ
Is flow5 now open source?
Yes. The v7.53 release notes state that flow5 is FOSS.
Will older versions open files saved by the new releases?
No. The release notes warn that newly saved .fl5 project files will not be readable by versions older than the version that created them.
Has IGES support been removed?
Yes. v7.54 states IGES import and export options were removed due to changes in OCC symbol names.
Are the features marked earlier to 'become active when flow5 goes open-source' now available?
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
Related posts
- Upgrade your car with an 11-inch Android Auto display and built-in 4K dashcam
- BusterMQ: Thread-per-core NATS server written in Zig with io_uring
- NERD: A terse, machine-optimized programming language for LLM-authored code