Research of the array spacing effect on wake interaction of tidal stream turbines

Abstract

Understanding the wake interactions among turbines is important for developing efficient tidal farm configurations. The present study compares the power and wake generated by a 2-row by 1-column array separated at three lateral spacings with those of a single tidal stream turbine. According to the results, power fluctuations increase with the tip speed ratio, with mean values corresponding to the inverse-u shape prediction of the blade element methods. For a single turbine, the cloud diagram of the lateral velocity deficit follows a half-elliptical contour with its center at the hub and initial covertices at the tip. The twin turbines largely exhibit these symmetric transversal distributions; however, they are doubled, with wake fusion occurring at the mid-width and closer with turbines approximation. The superposition of Gaussian-type velocity distributions matches the experimental bimodal functions with horizontally decreasing heights only after x > 6D. Vertically, the TIx in all conditions displays two strong areas, just above and below the turbine, owing to the interaction of the tip with tower vortices and the free and bed surface. In the two-unit arrangement, the blockage effect and the velocity of the mid-passage flow increase with the lateral separation of the turbines. This has a direct effect on wake combination, width, and recovery.