Abstract
In the case of tidal turbine arrays, the spatial evolution pattern of turbine wakes affects the power performance of other turbines and the hydrodynamic environment of adjacent turbines. However, the evolution mechanism is unclear, particularly in terms of wake energy restoration process. Therefore, we investigated the wake spatial evolution mechanism of a tidal current turbine experimentally. The experiment used a porous disc to simulate the turbine rotor based on the equivalence principle of force. An acoustic Doppler velocimeter and a strain gauge measured the time-varying velocities and flow loads, respectively. The momentum loss generated a wake zone in the downstream with enhanced turbulence originating from the boundary shear layer. Initially, the velocity deficit in the wake core increased as the shear layer spread inwards. Moreover, the disc blockage accelerated the flow, generating high momentum transported into the wake zone. However, the wake expansion and turbulence dissipation were limited until the shear-induced turbulence appeared at the wake centre. The kinetic energy in the wake region recovered significantly in the range x = (2D, 3D). As the wake moved downstream, further energy restoration was observed in the entire wake region. However, the rate of energy transformation decreased beyond 7D downstream.