Conceptual turbine design for Darrieus-Type wave energy converter

In this study, we designed a horizontal-axis Darrieus turbine for a wave energy converter (WEC) application, generating electricity from the naturally oscillating water near the breaking wave zone. The design goal is for a two-turbine system to provide sufficient power for the generator to achieve an average output power greater than 10 kW r.m.s. at 120 to 180 rpm. The developed full-scale turbines have an overall length and radius of 1580 mm and 1100 mm, respectively. Two 1:3 scale turbines were manufactured to evaluate their effectiveness in a test flume that simulates the expected underwater conditions. Each small-scale turbine was designed with three blades: one with a NACA6620 blade shape and the other with a NACA4420 blade shape. Both turbines were tested at various flow rates, and a stress test under a maximum speed of around 350 rpm was also performed. The speed obtained at different flow rates was recorded and used to determine the efficiency of each turbine. For the NACA6620 small-scale turbine, we achieved a normalized efficiency of about 20~23%, which leads us to conclude that further optimization is needed to reach our target efficiency of over 30%. Once a more optimized turbine and blade shape with higher efficiency should be developed, we plan to conduct field tests in the Seragaki littoral zone (Okinawa, Japan).