Similarity of wake characteristics for yawed wind turbines of utility-scale

Abstract

This work is dedicated to studying the influence of yaw angle on the wake characteristics of a 2.5 MW utility-scale wind turbine using large-eddy simulations with the turbine's blades and nacelle parameterized as actuator surfaces. Four different yaw angles are simulated, i.e., $γ=0^{\circ},10^{\circ},20^{\circ},30^{\circ}$ for three different tip-speed ratios $λ= 7,8,9$. Similarities are observed for both time-averaged velocity fields and the turbulence statistics of turbine wakes. Specifically, it is found that the temporal average of the wake deflection, the velocity deficit and the transverse velocity, the Reynolds stresses, and the wake width defined using the velocity deficit can be properly scaled using the characteristic length and velocity scales depending on the thrust on the rotor and yaw angles. The width of the region influenced by the transverse velocity, the PDF of the instantaneous wake position, and the standard deviation of wake position and wake width, on the other hand, are scaled well using the rotor diameter independent of the yaw angles and tip-speed ratios. These results suggest that the wake of a yawed wind turbine can be decomposed into the streamwise and transverse components, and the turbine-added turbulence and the meandering motion of the wake can be decoupled from the wake deflection for the considered cases.