Study on characteristics of turbine wake and the effect of array arrangement

Abstract

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.