Numerical Study on the Energy Extraction Performance of Coupled Tandem Flapping Hydrofoils

Tidal current energy is a promising renewable energy source for future electricity supply. The flapping hydrofoil is regarded as a useful tool to extract the tidal current energy in shallow water. A concept of coupled tandem flapping hydrofoils under semi-activated mode was proposed in the present study. A two-dimensional numerical model, based on the computational fluid dynamics software ANSYS-Fluent, was established to investigate the power extraction performance of the coupled tandem flapping hydrofoils. The effects of the reduced frequency, pitching amplitude,moment of inertia, damping coefficient, and longitudinal distance between hydrofoils were studied. The vortices,pressure distribution, and kinetic characteristics of hydrofoils under various conditions were analyzed to reveal the interaction between the shedding vortex and hydrofoils. The energy extraction mechanism and hydrodynamic performance were analyzed. The positive interactions for energy harvesting were identified for improvements of the further performance. The peak values of efficiency and power coefficient were achieved at 0.69 and 2.13,respectively.