Influence of Airfoil Curvature and Blade Angle on Vertical Axis Hydraulic Turbine Performance in Low Flow Conditions

The vertical axis hydrokinetic turbine is increasingly being used as a renewable energy device to harness tidal energy. In coastal regions with low tidal flow velocities, vertical-axis hydrokinetic turbines often exhibit low energy conversion efficiency, limiting their engineering applications. However, research in this field lacks systematic reviews and reliable solutions for improving efficiency. The paper, based on the traditional vertical axis hydrokinetic turbines, utilized numerical calculations and experimental methods to investigate the effects of blade helicity and airfoil curvature on the energy conversion efficiency of vertical axis hydrokinetic turbines in low flow velocity conditions. Additionally, an improved vertical-axis turbine model is proposed to enhance energy conversion efficiency in low-flow environments. The results indicate that increasing the blade helical angle and airfoil curvature can better optimize the flow conditions around the turbine, significantly improving the energy conversion efficiency of vertical axis turbines. The airfoil blade with a 20% curvature performs best at blade angle, with its power coefficient curve reaching higher peak values at several azimuth angles. At this point, the maximum efficiency reaches 24.42%. Compared to the conventional straight-blade design, the improved turbine model exhibits 6.13% increase in average energy capture efficiency, 3.70% increase in average dynamic torque, and 11.1% improvement in self-starting performance. Comparative analysis reveals that vertical-axis helical blade turbines exhibit superior hydrodynamic performance under low-flow conditions, effectively overcoming the limitations of conventional straight-blade turbines, including poor self-starting capability and low efficiency. This research provides valuable insights into improving the performance of vertical-axis turbines in low-flow environments and suggests innovative solutions for optimizing turbine design.