The Behavior of Vertical Axis Water Turbine With Flexible Blades: Self-Start, Ventilation, and Cavitation

Abstract

Three-bladed Darrieus-type vertical axis water turbine is a promising solution for producing electricity with minimal impact on the environment. Although considered a viable option, straight-bladed Darriues-type turbines have not been used commonly due to various operational issues; self-start and stall at low water speeds while ventilation and cavitation are limiting at high water speeds. In this study, the use of flexible blades with an aspect ratio of 2.21 is investigated at water velocities of 0.34, 0.51, 0.68, and 0.85 m/s experimentally. A stiffer turbine that has an 85–95 Shore A hardness blade starts to rotate at 0.51 m/s flow velocity. The more flexible turbine that has a 75–85 Shore A hardness blade starts to rotate at lower water velocities and experiences low rotational speeds resulting in an improved self-start. However, low rotation speed will cause a reduction in the coefficient of performance (Cp). High-speed imaging of the flow field also shows that a low tip speed ratio (TSR) helps to prevent the occurrence of ventilation and cavitation for the turbine with 75–85 Shore A hardness blades.