Seasonal variability of Offshore Wind Turbine Wakes

Abstract

The seasonal variations in the stability of the offshore atmospheric boundary layer (ABL) are more significant than diurnal variations because of the high specific heat capacity of water. Atmospheric turbulence is strongly influenced by the atmospheric stability and therefore the variations in wind speed and atmospheric stability are important to wind turbine operations since they affect the power production and fatigue loading. In this study, wind turbine wakes in a wind farm are modelled using Large Eddy Simulation (LES). The air and ocean temperatures and wind speeds measured by a floating buoy are used to prescribe the surface heat flux and wind speed for the simulations. The results show that the wind farm efficiency in winter (unstable ABL) is approximately 20% higher than in summer (stable ABL). The dynamic loads of the upstream turbine were lower in summer due to the weaker ambient turbulence intensity of the stable ABL. The magnitudes of the dynamic loads in winter and summer are comparable, particularly in the high frequency range.