Three-dimensional numerical analysis on blade response of a vertical-axis tidal current turbine under operational conditions

Abstract

Tidal current as a large-scale renewable source of energy has received significant attention recently. The technology used to harvest energy from tidal current is called a tidal current turbine. Although some of the principles of wind turbine design are applicable to tidal current turbines, to ensure long-term reliability in tidal current turbines, designers must consider elements such as cavitation damage and corrosion. Depending on the orientation of axis, tidal current turbines can be classified as vertical-axis turbines or horizontal-axis turbines. Existing studies on the vertical-axis tidal current turbines focus more on the hydrodynamic aspects of the turbine rather than the structural aspects. This paper summarizes our recent efforts to study the integrated hydrodynamic and structural aspects of vertical-axis tidal current turbines. After reviewing existing methods for modeling tidal current turbines, we developed a hybrid approach that combines a discrete vortex method with a finite element method that can simulate the integrated hydrodynamic and structural response of a vertical-axis turbine. This hybrid method was employed to analyze a typical three-blade vertical-axis turbine. The power coefficient was used to evaluate the hydrodynamic performance, and critical deflection was considered to evaluate the structural reliability. A sensitivity analysis was also conducted with various turbine height-to-radius (H/R) ratios. The results indicated that both the power output and failure probability increase with the turbine height, suggesting a necessity for optimal design. The optimization of a three-blade vertical-axis turbine design using the hybrid method yielded a turbine H/R ratio of about 3.0 for reliable maximum power output.