Large-Eddy Simulations of wind turbine wakes in sheared inflows

Modern-day wind turbines are growing continuously in size and reach diameters of more than 200m in an effort to meet the fast growing demand for wind energy. As a consequence, the rotors are exposed to larger velocity variations in the approach flow due to the presence of shear, veer and turbulence. The shear of the ambient flow is an important effect that can impact the wake of a turbine twofold: one way is how the wake evolves in the sheared flow; the other way is by impacting the performance and loading of the turbine and, hence, the wake it produces. Both ways can affect the size, shape, spreading and recovery of the turbine wake and, consequently, impact on loads and power output of turbines located downstream. In this study, we analyzed the influence of different inflow wind shear configurations on the evolution of the wake behind the IEA 15MW reference wind turbine by means of high-resolution Large-Eddy Simulations. In order to isolate the shear effects, the mean and hub height wind speed of the inflow was kept constant by prescribing linear shear profiles without turbulence. The influence of Coriolis forces and thermal stratification are neglected. In addition, the effect of the imposed shear on the turbine's power and thrust, and the effect of including the nacelle in the simulation, were monitored.