Abstract
Investigating the wake structure and its recovery of a twin-rotor tidal turbine is of great significance to the development of such a kind of tidal turbines. Experiments were carried out in the circulating flume by using the Acoustic Doppler Velocimetry to study the wake characteristics of a twin-rotor tidal turbine, considering impacts of rotor spacing and rotors rotation direction. The experimental results show that the near wake behind the rotor is independent of each other, while the wakes start mixing into one at certain distance downstream. With an increase of rotor spacing, the mixing position gradually approaches the turbine. The turbulence intensity on the central axis of the two rotors is obviously larger, which is caused by the mutual interference between the twin rotors and the blockage effect of pile. Different rotors rotation directions affect the recovery of flow velocity behind these two rotors.