Observation and Large Eddy Simulation of Coastal Winds at Anholt Offshore Wind Farm

Abstract

LiDAR and wave buoy data from the Anholt offshore wind farm have been analysed to determine the seasonal variability of the coastal winds. The wind shear exponent and turbulence intensity were used to classify the atmospheric stability. The occurrence of a Low- Level Jet (LLJ) event in the offshore environment was also studied. Three different periods that represent near-neutral, unstable, and stable atmospheric stratification were chosen for comparison with Large Eddy Simulation (LES) results. The LiDAR data showed that the atmosphere can be typically classified as unstably stratified in summer, while near-neutral stratification was frequently observed in winter. These resulted in higher mean wind speeds, wind velocity shear and directional shear in winter with lower turbulence intensity (TI). The occurrence of LLJ was found to be highest at a wind speed of 6 m/s at 86 m height, and the most frequent maximum velocity in the LLJ was observed between approximately 126 m and 186 m. For the wave data analysis, sea surface roughness was calculated using the wave steepness method, and it was found to be generally less than 0.4 mm, while the wind and wave misalignment was frequently less than 30°. The LES results matched the LiDAR profiles well for all atmospheric conditions, even though LES slightly underestimated the Turbulent Kinetic Energy (TKE) and directional shear for near-neutral conditions.