Enhancing the efficiency of a gravitational water vortex turbine through blade length and exit angle optimization

GWVTs make possible micro-hydropower at ultra-low heads where conventional turbines are impractical. This study targets the persistent gap of suboptimal runner design and outlet losses through the optimization of a radial closed-hub GWVT for reliable high-efficiency operation under low head. The contribution of this research is a compact, reproducible CFD-Taguchi L9 workflow ranking runner parameters by importance, linking vortex descriptors to performance; the research contribution is an engineering design map (N, L, β₁, β₂) that can be directly applied at low-head sites. Methods include the use of free-surface CFD (VOF, steady RANS k–ε, MRF) together with a mesh-independence study and a Taguchi L9 array to span the number of blades, N, blade length, L, entry angle, β₁, and exit angle, β₂. Simulations were run at Q ≈ 0.6 m³/s and H ≈ 0.86 m; torque/efficiency and flow fields (λ₂ iso-surfaces, VOF α=0.5) were analyzed. Results indicate torque plateaus from ≥0.8 million cells; a ≈2.22-million-cell grid offers a sound accuracy-cost trade-off. The main-effects ranking is L > β₂ > N ≈ β₁. The optimum (N=13, L=45°, β₁=11.51°, β₂=3°) provides 628 N·m and ≈58.8% efficiency (≈+89% torque vs. baseline), along with a deeper, more axisymmetric core with cleaner discharge. This implies that the most effective levers for performance are lengthening the blades and minimizing the exit angle. This workflow now provides a practical path to robust design. Confirmation runs, URANS/LES, and prototype testing will follow in due course, and generalization to field conditions will be carried out.