Development of a bidirectional horizontal-axis tidal stream tip-connected turbine

Abstract

Tidal current power generation offers predictable energy output but faces challenges such as low power density, structural requirements, and degradation due to corrosion and biofouling. In this study, a novel tip-connected turbine is proposed to address these issues. The turbine features an increased blade area to enhance torque under low flow velocity conditions and a tip-connected structure to improve blade strength and suppress tip vortices. In addition, a symmetrical hydrofoil is adopted to enable operation under reciprocating flow without yaw control. Based on a six-bladed horizontal-axis turbine designed using blade element momentum theory, two types of tip-connected turbines—ring-shaped and square-shaped—were developed. Performance tests and numerical simulations were conducted. The square-shaped turbine exhibited higher power coefficients than the ring-shaped turbine, with qualitative agreement between experiments and simulations. Comparison with two-stage turbines without tip connection confirmed that tip vortices are suppressed by the tip-connection structure. Flow analysis also showed reduced radial flow in the square-shaped turbine. These results demonstrate that appropriate design of blade shaft linearity and tip-connection geometry can improve turbine performance.