Design and experimental validation of a novel asymmetric airfoil turbine with mechanical rectification for OWC systems: A comparison with an impulse turbine

Existing oscillating water column wave energy device designs have an inherent limitation whereby air turbines are forced to adopt symmetrical configurations to accommodate bidirectional airflow. The low starting torque of Wells turbines caused by symmetrical airfoils and the excessive airflow resistance in impulse turbines induced by stators are a direct consequence of this symmetrical limitation. To address this challenge, a novel asymmetric airfoil turbine is proposed that integrates the SG6043 asymmetric airfoil with a mechanical rectification structure based on a one-way clutch. By utilizing mechanical rectification to break the geometric symmetry constraint of the rotor, combined with Wilson's theory and an additive manufacturing approach, the aerodynamic correction and precision manufacturing of a micro-scale prototype operating at low Reynolds numbers were achieved. Comparative wave tank experiments demonstrate that, benefiting from the low damping characteristics of its open flow passages, the proposed turbine achieves linear impedance matching with the air chamber, effectively overcoming the power truncation phenomenon of a traditional impulse turbine under higher waves, specifically for wave steepness of ka ≥ 0.08 within the near-resonance wavenumber band. Under design conditions in scaled experiments, the peak electrical power of the asymmetric turbine increases exponentially with wave height, reaching approximately 2.4 times that of the impulse turbine under identical conditions. More significantly, even under the restricted half-cycle work condition utilizing only the exhalation stroke, its average output power still significantly surpasses that of the fully operational impulse turbine. This efficiency inversion strongly confirms the potential of the asymmetric lift-based rotor assisted by mechanical rectification for high-density energy capture far exceeding that of traditional configurations.