Study of the hydrodynamic characteristics of the blade based on a bionic hydrofoil at low flow velocity

The flow velocity of seawater is relatively low compared to wind speed; however, the density of seawater is much higher than that of wind, and its energy density is more than 800 times higher than that of wind energy. The traditional turbine hydrofoil design is usually based on the NACA airfoil, which is commonly used in wind power generation. However, owing to the significant differences in the fluid properties of water and wind, the energy capture efficiency of the blades is unstable under low-flow sea conditions. This study investigated the hydrofoils of blades under low-sea conditions and proposed a thin-arc, large-curvature hydrofoil based on the elytra of beetles and ladybirds flying at low Reynolds numbers. The NAGA-II multi-objective genetic algorithm combined with the CST method was used to parametrize and optimize the two hydrofoil curves, and the hydrodynamic performance of the optimized hydrofoil was tested and analyzed using the STAR-CCM + fluid simulation software. The results show that compared with the traditional NACA airfoil, the proposed thin-arch large-curvature hydrofoil has a better coefficient of lift and a higher coefficient of pressure under low flow velocity and high angle of attack conditions. Through a comprehensive comparison of several design schemes, the ladybird bionic hydrofoil with better lift-to-drag ratio stability was finally determined for turbine blade design. The hydrodynamic characteristics of a three-dimensional bionic blade were numerically simulated and experimentally tested. The results show that when the blade pitch angle is 15°, the design can achieve a higher power coefficient and lower thrust coefficient over a wider flow velocity range, indicating a more balanced design characteristic. This verifies the correctness and effectiveness of the proposed design method. •Proposes a novel thin-arc, large-curvature airfoil inspired by beetles and ladybirds for low Reynolds number flows.•Uses NAGA-II genetic algorithm and CST parameterization for multi-objective hydrofoil shape optimization.•Demonstrates superior lift and pressure coefficients at low speeds and large angles of attack.•Ladybird bionic hydrofoil improves blade design due to enhanced lift-to-drag stability.