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.

In this paper, based on the CFD software ANSYS-Fluent, two-dimensional numerical models are established to investigate the hydrodynamic performance of a self-starting H-Darrius vertical axis tidal turbine (VATT) array of three turbines in a triangular layout with 3D in axial and radial distance. Three main aspects are explored in this study: (1) the self-starting performance, power coefficient, flow fields, and blade force of the double-row VATT array, which are compared with a stand-alone turbine, (2) the wake development of the front and rear displacement turbines, and (3) the feasibility of the double-row self-starting VATT array in practical applications. It is found that the power coefficients of the three turbines in the array all improved compared with that of the stand-alone turbine, and as the load increased, the difference between the averaged power coefficient of the array and a stand-alone turbine was more obvious, with a maximum difference of 3%. The main effects of the front turbines on the rear turbine are energy utilization and turbine vibration. Due to the beam effect between the front turbines, the incident flow rate of the rear turbine increased to approximately 1.2 times the free flow rate. However, the greater rotational fluctuations of the rear turbine mean that although it had a higher power factor, it was more susceptible to fatigue damage. The wake of the rear turbine in the array had a much larger area of influence on both the length and width, but the velocity deficit recovered more quickly to over 95% at a distance of 10D behind it. The rate of wake velocity recovery is load-dependent for a stand-alone self-starting turbine, but this was not evident in the arrays. The positive torque of the turbine is mainly generated when the blade rotates through an azimuth angle from 45° to 160° and mainly benefits from the inner side of the blade. For the double-row three-turbine array, the axial and radial spacing of 3D is reasonable in practical applications.

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