Numerical investigation of the power extraction mechanism of flapping foil tidal energy harvesting devices

The flapping foil hydrokinetics turbine is a new method to generate energy from incoming flow field. The numerical simulations have been performed computationally by using two-dimensional unsteady Reynolds-averaged Navier–Stokes equations. It was found that the maximum energy efficiency reached about 35.2% when the reduced frequency was 0.11; at this time, the foil experienced a light dynamic stall and two opposite-sign vorticities were shed from the foil per half of the cycle. This report also studied the energy extraction performance of flapping foil device and the correlation between the foil kinematic parameters and the flow fields around it at actual operating Reynolds number comprehensively. In addition, the vortex variation and the pressure coefficient distribution along the foil’s surface were used to demonstrate the mechanism of flapping foil energy generation turbine. The creation and shedding of the leading edge vortex played the critical role in energy transformation between the flow fluid and energy harvesting systems. Therefore, if the timing of the leading edge vortex generation and shedding is controlled, the energy extraction efficiency can be increased considerably