The Impact of Ambient Turbulence on Wind Turbine Wakes

Wind turbine wakes and their interactions with atmospheric boundary layer (ABL) flows have a significant impact on the performance of wind turbines and wind farms, and thus it is essential to understand the flow dynamics imposed by ABL flows and wind turbine wakes. In this study, we focus on the impact of ambient turbulence on wind turbine wakes in the neutral ABL. Full rotor models, including the nacelle and tower, for the National Renewable Energy Laboratory (NREL) 5MW reference turbine were established. CFD simulations using a Reynolds-averaged Navier-Stokes (RANS) framework were carried out under various turbulence levels (low-turbulence case: 1%; medium-turbulence case: 5%; and high-turbulence case:13%, 20%) in the neutral ABL, and two turbulence closure schemes, Standard k-ɛ, and Reynolds Stress Models (RSM) were utilized in concert to achieve better effects. In addition, velocity deficit, wake dimensions and wake asymmetries were calculated and analysed. The simulation results show that the development of wind turbine wakes presents a certain dependency on the imposed level of turbulence. Higher ambient turbulence leads to faster wake recovery. In addition, obvious asymmetries were observed in near wake region.