  Reducing wake losses in wind farms by deflecting the wakes through turbine
yawing has been shown to be a feasible wind farm controls approach.
Nonetheless, the effectiveness of yawing depends not only on the degree of wake
deflection but also on the resulting shape of the wake. In this work, the
deflection and morphology of wakes behind a wind turbine operating in yawed
conditions are studied using wind tunnel experiments of a wind turbine modeled
as a porous disk in a uniform inflow. First, by measuring velocity
distributions at various downstream positions and comparing with prior studies,
we confirm that the non-rotating wind turbine model in yaw generates realistic
wake deflections. Second, we characterize the wake shape and make first
observations of what is termed a curled wake, displaying significant spanwise
asymmetry. The wake curling observed in the experiments is also reproduced
qualitatively in large eddy simulations using both actuator disk and actuator
line models. When a wind turbine is yawed for the benefit of downstream
turbines, the asymmetric shape of the wake must be taken into account since it
affects how much of it intersects the downstream turbines.
