Flow-driven optimization of power augmenters for performance enhancement of Savonius-based power take-off in oscillating water column systems

Oscillating water column (OWC) devices are a promising technology for wave energy conversion, in which the efficiency of the power take-off (PTO) system plays a critical role. Savonius turbines are attractive candidates for OWC applications due to their mechanical simplicity, robustness, and inherent self-rectifying capability under bidirectional airflow; however, their aerodynamic performance is intrinsically limited. This work aims to enhance the performance of Savonius-based PTO systems through the aerodynamic optimization of external power augmenters. An experimental campaign was conducted on a scaled Savonius turbine operating under bidirectional, oscillatory airflow at two frequencies (0.1 and 1 Hz). A transient computational fluid dynamics (CFD) model based on a sliding mesh approach and dynamic fluid body interaction was developed and validated against experimental data. The numerical framework was then coupled with an optimization algorithm to refine the geometry of the power augmenters, with the objective of maximizing the turbine tip speed ratio. The optimized configuration showed a significant improvement in performance compared to both the bare turbine and the baseline power augmenter design. The maximum tip speed ratio increased by up to 52% at 1 Hz and 58.2% at 0.1 Hz, while the maximum power coefficient increased by up to 12.7%. Flow-field analysis revealed enhanced flow acceleration toward the driving scoop and reduced aerodynamic losses under both maximum and minimum thrust conditions. These results demonstrate the effectiveness of CFD-driven optimization for improving Savonius turbine PTO performance in OWC systems.