The Effect of the Mass Moment of Inertia on Vertical Axis Current Turbines

Abstract

Abstract. This study examines how an increased mass moment of inertia affects the performance of the vertical axis current turbine (VACT). Increasing the moment of inertia of the rotor has been proposed as a potential strategy to improve torque stability and smooth power output under low flow conditions. This is made using the VAACT (vertical axis autorotation current turbine) with an S-shaped blade by performing tests 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 m in length, 1.4 m in width, and 0.5 m in water depth, resulting in a blockage ratio of 21%. The experiments varied the moment of inertia from 0.80kgm2 to 3.0kgm2 at Reynolds numbers ranging from 75,000 to 135,000. The power output was estimated using a weight-lifting power take-off (PTO), also known as mechanical PTO, where the power is calculated by the time derivative of the weight’s potential energy. The results show that additional mass moments of inertia can improve the turbine’s power harvesting by about 60% compared to the scenario without increased mass moment of inertia (Soares et al., 2023, “The Effect of Power Take-Off System on S-Shaped Vertical Axis Autorotation Current Turbine,” Proceedings of the ASME 2023 42nd International Conference on Ocean, Offshore and Arctic Engineering, Melbourne). Moreover, the tests indicate that increasing the mass moment of inertia stabilizes the turbine 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 0.75, a Reynolds number of 75,000, and a dimensionless moment of inertia of 1.160.