Study on energy harvesting performance of a tidal current turbine based on three pitching circular motion hydrofoils using numerical method

If the pitching hydrofoil moves following a circular trajectory, the turbine can use multiple hydrofoils to capture energy from the current, which has the potential to improve efficiency. In this study, by solving Reynolds- averaged Navier-Stokes equation with Shear Stress Transport k-omega model, hydrodynamic performance of the new turbine with three hydrofoils was investigated. First, energy harvesting performance of the turbine with a wide range of motion parameters was studied. Then, based on the optimal operating condition, energy harvesting principle of the turbine was analyzed from the perspectives of vortex-body interactions, hydrodynamic forces and energy parameters. Finally, the fundamental reasons for the variation of efficiency with motion parameters were investigated. Results show that the maximum efficiency reaches about 50%, much higher than that of turbines of the same type with one hydrofoil and the vertical axis turbine. The turbine harvests energy mainly through the circular motion and the lift is the main driving force for the turbine to harvest energy. At the optimal motion parameters, the interactions between vortex and hydrofoil is favorable, which increases the positive work done by the lift and reduces the energy consumed by the horizontal force and pitch moment at specific moments, thereby improving the efficiency.