The flow field within a staggered hydrokinetic turbine array

Hydrokinetic turbines are expected to improve the power yield from tidal currents, but their combination alters the flow field, which will, in turn, affect the power efficiency of the turbine array. This study carried out laboratory experiment to investigate the signature of the disturbed flow and its spatial evolution. Ten discs were arranged in a staggered layout of four rows, forming a streamwise inverted triangle. The velocity decreases by 73% as the approach flow passes through the first row, while the gap flow accelerates, with an increase of nearly 25% and 15% for the lateral and vertical interval flow respectively. With wake superposition, the velocity deficit is boosted, about 90% behind the fourth row, while the blockage speed-up effect is weakened. The wake velocity behind the first row further drops, up to 85% at 2D downstream, but this behaviour disappears for the subsequent rows. The enhanced secondary flow enters wake zones as the shear layers spread inwards. It, however, is lateral asymmetry and migrates from one side to the other with new rows addition. The array wake recovers insignificantly in the course of overlapped wakes decaying. It narrows abruptly as the next row is added, with the velocity deficit redistribution.