Numerical simulation on wake characteristics of wind turbines under different terrain parameters

The wake characteristics of wind turbines under different terrain geometric parameters (aspect ratio, relative height, horizontal scale) are conducted based on the large eddy simulation method combined with the actuated line model. The evolution of the interaction between terrain-induced separation flows and wake flows is analyzed. Results reveal that in hilly terrain with an aspect ratio of 1, the airflow is driven by terrain compression and acceleration effects to rise along the slope, reaching a maximum wind speed of about 16 m/s at the mountaintop. The critical slope for flow separation in complex terrain is about 0.3. In addition, the velocity losses across four hilltop terrains exhibit an M-shaped double-peak variation in the near-wake region, while displaying a U-shaped single-peak distribution in the far-wake region. The greatest difference between instantaneous and average velocity losses reached 31.8%. The velocity profile of the wind turbine wake at the mountain peak gradually decreases in the near-wake region, but gradually recovers in the mid-wake to far-wake region. The vortex characteristics in the near-wake region are dominated by terrain-induced separated flow, which gradually transitions to a significant coupling effect between the mountain terrain and the wind turbine wake. Moreover, the wind speed power spectral density reveals that terrain-induced separation vortices dominate in the near-wake region, while the far-wake region evolves into the coupled interaction between the wind turbine wake vortex and terrain vortices. The normalized frequency of 0.003 Hz corresponds to the dimensionless energy range of power spectral density, which ranges in magnitude from 10−5 to 10−4. The research results will provide valuable references for the micro-site selection and layout design of onshore wind farms.