Characteristics of wind turbine wakes for different blade designs

Abstract

In this work, we investigate the characteristics of wind turbine wakes for three different blade designs (i.e. the NREL-Ori, NREL-Root and NREL-Tip designs, where the NREL-Ori refers to the baseline offshore 5 MW wind turbine designed by the US National Renewable Energy Laboratory) under turbulent inflows using large-eddy simulations with the actuator surface model. The load on the blade is higher near the blade root/tip for the NREL-Root/NREL-Tip designs when compared with the NREL-Ori design, while their thrust coefficients are the same. The results show that the blade designs influence the velocity deficit in the near wake, turbulence kinetic energy and wake meandering (both amplitude and frequency). In the near-wake region, the magnitude of the velocity deficit from the NREL-Root design is higher. As for the turbulence kinetic energy, its maximum in the near wake is higher for the NREL-Tip design, while in the far wake, it is higher for the NREL-Root design. Analyses of the instantaneous spanwise wake centre positions show higher meandering amplitude for the NREL-Root design, with the magnitudes of the low-frequency components approximately the same as the other two designs under the same inflow. The dominant meandering frequencies from different designs are different, with lower values for the NREL-Root design for which the vortex structures near the hub of low frequency play leading roles, and higher values for the NREL-Tip design for which the flow structures of high frequency in the tip shear layer are more important.