Effect of Blockage Ratio on the Performance of a Ducted Savonius Turbine for OWC Applications

Savonius turbines are widely used in energy recovery applications due to their simplicity and the advantage of being self-aligning with the flow. These turbines can be employed for wind energy harvesting in urban environments as well as for wave energy recovery when integrated into an Oscillating Water Column (OWC) system. Furthermore, the ducted Savonius concept could be particularly suitable for OWC wave energy devices, thanks to its structural simplicity. This study investigates the effects of the ducted turbine blockage ratio on the performance of the system under steady and oscillating flow conditions. Specifically, a two-bladed Savonius turbine was tested in a dedicated experimental setup with a controlled airflow velocity (5 m/s). Three different blockage ratios (72.25%, 81.00%, and 90.25%) at a fixed overlap ratio (OR = 1/3) were analysed by varying the turbine diameter within a ducted configuration. For each blockage ratio, different oscillation frequencies of the airflow were tested to simulate the unsteady behaviour of OWC systems. In total, the performance of several operating conditions was evaluated to demonstrate how the blockage ratio influences turbine behaviour as the flow oscillation frequency varies. The findings provide insights into optimizing ducted Savonius turbines for improved efficiency in wave energy applications.