Wind turbine is the most frequently used device to extract the wind energy. Arising from the influences of various factors such as the high-frequency variation of incoming wind direction, it is difficult for the wind turbines to track the incoming wind timely. As a result of which, wind turbines inside the wind farm are commonly operated in a yaw state, known as yaw error, which can affect the wind farm performance. In the present work, taking a wind farm array with 12 NREL 5MW wind turbines as the research object, we conducted a series of large-eddy simulations under different incoming wind directions and surface roughness heights. The results reveal that yaw error can either increase the total power production or cause power loss of the wind farm array, depending on the change of wake effect. More seriously, the change in wind farm power caused by yaw error is not a small value, it can reach as much as 41.5% for the particular case considered here. This indicates that the influence of yaw error should be taken in wind farm power prediction in the real-world engineering.
Wind energy is one of the promising renewable resources with the advantages of pollution-free and low development cost. Horizontal axis wind turbine is the most frequently used device to absorb the wind energy (Chehouri et al, 2014). It is quite common that the wind turbine inside the wind farm operates in a yaw state, i.e., the rotor plane is not aligned with the incoming flow direction, arising from the following reasons: (1) The randomness of natural wind, which leads to a high-frequency change in inflow wind direction. (2) The lack of wind measuring instruments, which makes it impossible to provide accurate real-time wind monitoring data for all wind turbines inside the wind farm. (3) Wake effect and instantaneous turbulent structures in the atmospheric flow field, which can affect the wind measurement accuracy. (4) In order to ensure the stable operation of wind turbine, the yaw error threshold is commonly set in the real-world engineering, indicating that the yaw control action has a certain hysteresis.