Large-eddy simulation of an offshore wind farm under misaligned wind and wave conditions

The performance of offshore wind farms is significantly influenced by wind and sea state. This study employs large-eddy simulation (LES) with an actuator line model to investigate the effects of wind–wave angle and wave age on wind farm power production and wake characteristics. A range of wave ages (c/u_* ≈ 30, 60, and 90, where c is the wave phase speed and u_* is the airflow friction velocity) and wind–wave angles (α₀ = 0° – 180°) are examined. The results reveal that swell aligned with the wind direction (α₀ = 0°) markedly enhances both power production and wake recovery, with the highest improvement observed at c/u_* ≈ 90. Regarding the wind–wave angle effect, wind farm power output increases by approximately 50.8%, 55.3%, and 75.7% at α₀ = 45°, 90°, and 135°, respectively, whereas it decreases by 4.3% at α₀ = 180° compared to the no-swell case. This improvement is attributed to swell-induced wake deflection. Further analysis shows that lateral and oblique swells cause turbine wakes to deviate from the mean wind direction, resulting in noticeable lateral displacement of the wake trajectory. Additionally, low- and high-speed streaks emerge alongside the deflected wakes, coinciding with regions of elevated turbulent kinetic energy.