Experimental study of wake characteristics in tidal turbine arrays

For the successful deployment of large scale tidal turbine arrays occupying a large part of tidal channels, understanding the effects of wake interaction in densely spaced arrays is of importance. A comprehensive set of experiments has been conducted with scaled tidal turbines to investigate the resulting wake characteristics in a number of different staggered array configurations with up to four turbines on a designated support frame. Wake velocity deficits and turbulence intensities at a number of locations within and downstream of the array are presented and in addition the flow field recordings from Particle Image Velocimetry (PIV) measurements are presented for visual investigation of the resulting wake field and wake characteristics along the array centre line. The experiments show that lateral and longitudinal spacing variations of the individual devices vary the resulting flow field downstream of the array section significantly. Lateral spacing can be optimised to result in beneficial flow effects that accelerate the downstream wake recovery. Very close spacing however leads to significantly reduced velocity recovery. Longitudinal spacing shows less significant influence, especially for configurations with wide lateral distances. Differences in wake velocity deficit of up to 10% have been identified and suggest array wake recovery in and downstream of staggered sections, in areas of lower ambient turbulence levels, to be more significantly influenced by the lateral spacing especially towards the front rows of the array. With every additional array section the increasing turbulence intensity within the array is anticipated to reduce this effect.