The fluid mechanics of active flow control at very large scales

Losses due to wake interactions between wind turbines can significantly reduce the power output of wind farms. The possibility of active flow control by wake deflection downstream of yawed horizontal-axis wind turbines has motivated research on the fluid mechanics involved. We summarize the findings of a wind tunnel study (Bastankhah & Porte-Agel, J. Fluid Mech., vol. 806, 2016, pp. 506-541) of the flow associated with a yawed model wind turbine, and the insights and modelling developments that have followed this important study.