Fluid dynamics analysis of passive oscillating hydrofoils for tidal current energy extracting

A passive oscillating hydrofoil energy extracting technology that imitates the tail swinging of aquatic organisms to extract energy from flow field is presented in this paper, as an alternative to conventional rotating blades turbine. On the basis of analysis of the relationship between the movement characteristics of oscillating hydrofoil and the parameters including power coefficient, efficiency and reduced frequency, the device based on passive oscillating hydrofoil to extract tidal current energy is designed. The investigation is undertaken over a wide range of kinematic parameters including pitching amplitudes, heaving amplitudes and reduced frequency. The results reveal that the power extracted from the oncoming flow mainly comes from the heaving motion and the energy contribution from pitching motion is quite limited. Detailed examination of the motion parameters indicates that when the heaving amplitude reaches one chord length, the pitching amplitude reaches 70° and the reduced frequency reaches 0.11, the highest power extraction efficiency can reach 34.7%.