Numerical simulations of asymmetrical wake flows of a yawed wind turbine

Active yaw angle control is one of the promising methods for wind farm power optimization, it is implemented by intentionally misaligning the upwind turbine to the incoming wind direction, as a result, the wake is deflected away from the downwind turbine, and the latter turbine can extract more energy from the un-waked flow. For an application of such an operational control, it is important to have a good knowledge about the wake characteristics by a yawed wind turbine. However, studies on the symmetry to yaw direction have not sufficiently covered until now. Hence, in this paper, numerous large eddy simulations are performed, to investigate the wake properties of wind turbines with same yaw angle magnitude but opposite directions, and to further explore the effects of asymmetry in wake steering on wind farm performance. We find that the wake shape and wake deflection magnitude are asymmetrical for positive and negative yaw angles. What’s more, clockwise and counter-clockwise upstream turbine yaw rotations do not produce equal benefits at the downstream wind turbines. More importantly, it is observed that rows of turbines compound the effects of the asymmetry in wake steering, the power gain in the positive yaw case greatly exceeds the negative one. According to the detailed analysis of the yawed turbine wake in oppositely signed yaw angles, we encourage to incorporate the effects of asymmetry in wake steering into the empirical engineering wake models used for designing wind farm controllers.