Experimental study on aerodynamic performance of mixed-flow air turbine for oscillating water column wave energy converter

Air turbine is a critical component of oscillating water column (OWC) wave energy converter (WEC). Most existing air turbines suffer from either low energy conversion efficiency or high manufacturing complexity. To address these drawbacks, this paper proposes a mixed-flow air turbine and conducts experimental research on the aerodynamic performance of an OWC WEC equipped with this turbine. The effects of regular waves, irregular waves, rotor speed, and air chamber-turbine coupling on the aerodynamic power and conversion efficiency of the device are investigated. The results show that under regular waves, the aerodynamic power and turbine output power of the device exhibit a double-peak characteristic. Under irregular waves, the power presents a single-peak pattern, and the effective energy capture bandwidth is slightly widened. As the wave height increases, the aerodynamic power rises while the conversion efficiency decreases, with the highest total efficiency achieved at a wave height of 5 cm (17.3% for regular waves and 18% for irregular waves). Increasing the rotor speed can improve the turbine output power but will strengthen the suppression of water column movement in the air chamber, so it is necessary to balance the matching with air chamber resonance. Experiments have verified that the mixed-flow air turbine demonstrates stable energy conversion capability under various wave conditions. The above findings provide support for the structural optimization and operation control strategy formulation of mixed-flow air turbines.