Abstract
Usage of tidal energy attracted great interest in the field of in-situ and long-term observation based on facilities such as offshore floats and subsurface buoys. However, the periodic variation in the current direction due to the tidal evolution limits complete utilizing of such power source since most of the turbines has a limited ability to orient with the current. In this study, in order to improve the power generation efficiency of the turbine in the tidal condition, a duct structure for the turbine, which realizes the self-adaptive orientation with respect to the current direction, is developed. The structure also leads to flow enhancement in the turbine for a more efficient energy conversion. The key geometric parameters that affect the hydrodynamic property of the duct structure are investigated through numerical simulation. Self-orientation and flow enhancement ability of the duct structure developed is confirmed by both laboratory-scale water-channel experiment and offshore test.