The Effect of Extra Mass Moment of Inertia on S-Shaped Vertical Axis Autorotation Current Turbine (VAACT)

This study examines how the extra mass moment of inertia affects the performance of the S-shaped Vertical Axis Autorotation Current Turbine (VAACT). Tests were performed at the Laboratory of Waves and Currents (LOC-COPPE/UFRJ) to obtain the efficiency curves of this geometry. The test facility has dimensions of 22 meters in length, 1.4 meters in width, and 0.5 meters in water depth, resulting in a blockage ratio of 21%. The experiments were performed by varying the moment of inertia from 0.0135 kg · m2 to 3.0 kg · m2 at Reynolds numbers ranging from 30,000 to 135,000. The power output was estimated using a weight-lifting approach, where the power is calculated by the time derivative of the weight’s potential energy. The results show that additional mass moment of inertia can improve the turbine’s power harvesting by about 60%. Moreover, the tests indicate that increasing the mass moment of inertia stabilizes VAACT’s dynamics and enables it to operate at the design tip speed ratio. Additionally, the analysis reveals that the turbine’s efficiency can reach 25% when operating at a tip speed ratio of 1.5, a Reynolds number of 90,000, and a dimensionless moment of inertia of 1.160. However, the turbine’s performance at higher Reynolds numbers is poor due to the high vortex-shedding observed in the wake.