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A prerequisite in undertaking large-scale developments and utilisation of tidal current energy is to comprehend the hydrodynamic characteristics of the wake field of tidal current turbines. The wake of an upstream turbine can strongly affect the power output of downstream turbines and their arrangement. The structure of turbine wakes was investigated. One experiment was conducted on a two-bladed horizontal turbine in a laboratory flume. Actuator disc momentum theory, combined with Reynolds-averaged Navier–Stokes equations, was used to parameterise the tidal turbine. The numerical model was validated using experimental data. The degree of wake mixing improved when the axial distance was eight times the turbine diameter (8D) or larger. The influence of the arrangement and spacing of turbines was investigated at two tidal farms, one with three aligned turbines and one with seven staggered turbines. The incoming flow velocity of the downstream turbine was reduced by 31% when turbines were linearly aligned. The extent of influence of the third column was larger than that of the second column, indicating an expanding wake. Different lateral spaces of staggered turbines were analysed. Different distances between rows strongly influenced both the incoming velocity of downstream turbines and the expansion of the whole wake. The incoming flow of the third column reduced by 31, 17 and 16% with increasing lateral space. The flow velocity increased as water passed over the turbine tip. For staggered turbines, a centreline spacing of up to 1.5D for adjacent rows is recommended.

Two numerical wake model were established, one based on full geometry turbine and one based on actuator disc theory. The Actuator disc momentum theory assumes turbine as a constant sink of momentum in numerical domain. Results of numerical models were compared with experimental results, the experimental data is in good agreement with the simulation data. The difference between two models were analyzed in detail. The the difference between simulation results of actuator disc and test results are slightly larger in near wake region, the difference gradually decreased as the axial distance increased. The lack of the simulation of rotation of the model may lead this difference. The effect to wake recovery of blockage ratio was studied using numerical model based on actuator disc theory, 11 cases were studied, the results showed that the blockage ratio can heavily effect the recovery speed of turbine wake. Along the centerline, the degree of wake recovery decreased as the blockage ratio increased before X/D=10.8, and the degree of wake recovery increased as the blockage ratio increased after X/D=10.8.