Wind Turbine Wakes and Wind Farm Performance: a Wind Tunnel Study

Wind energy is growing in popularity and is becoming one of the most profitable sources of renewable energy, thus a deeper characterization of the interaction between atmospheric boundary layer and wind turbines is needed. In this study wind tunnel tests of wind turbine wakes are carried out through hot-wire anemometry and multi-hole pressure probes in order to analyse the development of wind turbine wakes. Tests were performed on three-bladed downscaled wind turbine models immersed in uniform flow with different turbulence levels. Moreover, tests were also performed with wind turbines immersed in boundary layers characterized by different turbulence profiles and surface aerodynamic roughness. Wind turbine wake is characterized by a strong velocity defect in the proximity of the rotor and its magnitude and cross-dimension are strictly dependent on wind turbine performance. The distance of recovery of the wakes and diffusion of turbulence are found to be strongly affected by turbulence level of the incoming flow. A higher turbulence level is typically detected downstream of each wind turbine for heights comparable to the top-tip of the blades, which can produce increased fatigue loads on the following wind turbines within a wind farm. The effect of the wind farm layout on power production is also investigated by testing aligned and staggered wind farms with varying streamwise and spanwise separation distances. These measurements are also being used to test and guide the development of improved parametrization of wind turbines in high-resolution numerical models, such as large-eddy simulations (LES).