Numerical investigation into the hydrodynamic characteristics of water vortex turbines with varied blade angles

Water Vortex Hydro Turbines are a promising renewable energy solution for ultra-low-head applications, with performance strongly influenced by blade geometry in converting vortex-induced momentum into mechanical energy. This study numerically investigates the hydrodynamic characteristics including velocity distribution, air-core formation, and pressure gradient to determine the optimal blade angle using transient Computational Fluid Dynamics (CFD) with the Realizable k-ε turbulence model. A six-bladed turbine was analysed at blade angles of 75°, 90°, and 105° under a constant inlet velocity of 1 m/s. The results demonstrate that the 90° configuration delivers the best overall performance, with the maximum velocity increasing from 3.096 m/s (75°) to 4.376 m/s (90°), representing an improvement of approximately 41.4% and indicating a significantly stronger and more stable vortex structure. Although the 105° configuration reaches the highest peak velocity of 4.657 m/s, severe flow separation reduces flow stability and limits effective energy transfer. In terms of pressure, the 90° configuration produces the most favourable and symmetric gradient, with a maximum of 5777.397 Pa and a minimum of 3.154 Pa, compared to the more distorted distributions observed in the 75° and 105° cases (5741.087 Pa and 5892.066 Pa, respectively). Additionally, the 90° configuration generates a more compact and stable air-core, reducing hydraulic losses and enhancing fluid–blade interaction. Overall, the 90° blade angle provides the optimal balance between velocity magnitude, vortex stability, and pressure distribution, making it the most effective configuration for maximizing energy conversion in ultra-low-head water vortex hydro turbines.