Interactions between approaching flow and hydrokinetic turbines in a staggered layout

Laboratory experiments were conducted to investigate the interactions of the approaching flow and tidal turbine models in a multi-row array. Porous discs were employed to represent 10 horizontal axis turbines, which were arranged in a staggered configuration with four rows. The number of turbines decreased in the streamwise direction, so the 10 turbines formed an inverted triangle layout. An Acoustic doppler velocimeter and smart strain gauges were used to measure the flow velocity and thrust loads, respectively. The results show that the row-averaged efficiency primarily relies on the approaching flow velocity, which increases due to blockage effect, whereas decreases because of the wake velocity deficit. However, the local blockage effect is not apparent to the additional turbines deployed six turbine diameters downstream. As a result, the array performance is not improved as expected in a staggered configuration. Once the wakes superpose, the disadvantage of the wake shelter is reinforced while the advantage of the blockage acceleration is lost. The load instability becomes significant as the shear-induced turbulence is intensified, especially among the second-row turbines, but instability is ameliorated by wake overlapping. The study suggests that the streamwise inverted triangle configuration does not lead to as efficient array performance as expected.