Fish-tail-swing-inspired Geometric Optimization of Micro-turbine Blades Using Response Surface Methodology and Computational Fluid Dynamics

To improve the aerodynamic performance of micro air-driven turbine generator rotors, this study proposes a bio-inspired blade design method based on the tail-swing characteristics of carp. Unlike conventional bio-inspired approaches that primarily reproduce static biological contours, the proposed method translates different tail-swing postures into adjustable blade geometries. The swing angle, front arc angle, rear arc angle, and trailing-edge radius were selected as the design variables. A Box-Behnken design was used to generate 29 blade configurations, and transient CFD simulations were performed to determine the corresponding power coefficients. A response surface model was then established to quantify the individual and interaction effects of the geometric parameters on rotor aerodynamic performance and to identify the optimal blade configuration. The original rotor reached a peak power coefficient of 0.124 at TSR = 0.5. Among the 29 Box-Behnken design cases, the Case 15 rotor achieved a peak power coefficient of 0.315 at TSR = 0.8, representing a 154.0% improvement over the original rotor. The optimized rotor identified by the response surface model reached a peak power coefficient of 0.342 at TSR = 0.8, corresponding to a 175.8% improvement. Sensitivity analysis showed that the influence of the geometric parameters on the power coefficient followed the order: swing angle > rear arc angle > trailing-edge radius > front arc angle, with a significant interaction between the swing angle and rear arc angle. Flow-field analysis revealed that the bio-inspired blade configurations enlarged the high-pressure region over the middle and rear portions of the pressure surface while strengthening the corresponding low-pressure region on the suction surface, thereby increasing the pressure difference across the blade. The optimized blades also produced more continuous high-velocity flow within the inter-blade passages while reducing the extent of the low-velocity region near the trailing edge, promoting more continuous airflow acceleration and enhanced momentum transport. These findings provide a bio-inspired design strategy for improving the aerodynamic performance of micro air-driven turbine rotors and offer guidance for the aerodynamic optimization of small-scale rotating machinery.