Wake Structure in Yawed Approaching Flows for an AxialFlow Wind Turbine

Abstract

Effects of yawed wind turbines on the wake structure are not fully understood. To obtain a better understanding, numerical studies of a smallscale threebladed horizontal axis wind turbine at tip speed ratio (TSR) = 6.7 with yaw angles of zero, 15 deg, 30 deg, and 45 deg have been carried out to investigate the wake characteristics of the turbine in the near and farwake. A hybrid approach coupling large eddy simulation (LES) with actuator line modeling (ALM) has been employed in the present study. The predicted results confirm the previous finding that the turbine wake is asymmetric under yawed approaching flows and the wake is inclined to the direction where the rotor is yawed. The present work further demonstrates that at high yaw angles the main wake may be divided into two smaller parallel wakes further downstream that are not symmetric suggesting a dependency on the turbine rotation direction. This study quantitatively explains how the nonuniform variations of radial velocity components at the turbine plane caused by the yawed flows result in the wake deflection and intersection of hub and blade tip vortices further downstream which leads to the wake splitting at high yaw angles.