Replacing wakes with streaks in wind turbine arrays

Abstract

Wind turbine wakes negatively affect downwind turbines in wind farms reducing their global efficiency. The reduction of wake-turbine interactions by actuating control on yaw angles and induction factors is an active area of research. In this study, the capability of spanwise-periodic rows of wind turbines with tilted rotors to reduce negative wake-turbine interactions is investigated through large-eddy simulations. It is shown that, by means of rotor tilt, it is possible to replace turbine far wakes with high-speed streaks where the streamwise velocity exceeds the freestream velocity at hub height. Considering three aligned rows of wind turbines, it is found that the global power extracted from the wind can be increased by tilting rotors of the upwind turbine rows, similarly to what is already known for the case of a single column of aligned turbines. It is further shown that global tilt-induced power gains can be significantly increased by operating the tilted turbines at higher induction rates. Power gains are further increased for higher ratios of rotor diameters and turbine spacings to the boundary layer height. All these findings are consistent with those of previous studies where streamwise streaks were artificially forced by means of spanwise-periodic rows of wall-mounted roughness elements in order to control canonical boundary layers for drag-reduction applications.