: Reduced computation time for complex mesh grids by approximately 15% compared to v.2.20.

| Test Case | v2.20 Time (s) | v2.21 Time (s) | Speedup | Memory (v2.21) | |-----------|----------------|----------------|---------|----------------| | Lid-driven cavity (512x512 uniform) | 342 | 118 | 2.9x | 2.1 GB | | NACA0012 (150k cells, SST k-ω) | 890 | 412 | 2.16x | 4.7 GB | | Dam-break VOF (1M cells) | 2,150 | 688 | 3.12x | 9.8 GB |

The FF2D development team (currently 6 core contributors) has published a roadmap through 2026:

– The transition SST and VOF models make v2.21 publishable. Cite the forthcoming 2025 paper in the Journal of Open Source Software .

was released as a stability and compatibility milestone. Where previous versions (such as v.2.19 or v.2.20) may have struggled with specific memory allocations or newer operating system architectures, v.2.21 represented a maturation of the codebase. It is widely regarded by its user base as the "stable baseline"—a version reliable enough for production environments where consistency is paramount.