Coupled effects of 3D wake expansion and terrain anisotropy on downstream wind turbine power performance and fatigue load

The power performance and fatigue load of downstream wind turbine (WTdown) under different terrain complexities (flat terrain, windward slope, and leeward slope) are directly related to the economic viability and safety of wind farms. For an efficient and accurate evaluation of power performance and fatigue load, a computational framework was developed based on the proposed 3DJG-CT wake model and aero-elastic-servo simulation for WT, which fully considers the coupling effects of wake expansion and terrain anisotropy. The fidelity of this simulation framework was verified by the rotor power design value and field-measured data under uniform inflow conditions. Comprehensive analysis of the power performance and fatigue load of WTdown at various relative positions was conducted in complex terrain with realistic varied configurations. Results show that the rotor power deficit rate in flat terrain cases ranges from 16.52 % to 54.71 %, increasing to 42.69 %–77.80 % in leeward slope cases at upstream velocities of 6–10 m/s. Comparative analysis of the results of the 1.5 MW and 5 MW WT indicates that the size effect of the turbine rotor significantly influences momentum mixing and wake expansion characteristics, thereby affecting the power recovery of WTdown. Increasing crosswise distance between WTs can enhance power output but also amplify the unbalanced aerodynamic load on WTdown. Due to terrain anisotropy and wake deflection, the damage equivalent load (DEL) at blade root of WTdown increases by an average of 136.57 % in windward slope cases compared to flat terrain cases. The fluctuation and magnitude of load alternately play the dominant contribution on DEL as the inflow velocity increases. Better guidance for power performance evaluation and fatigue estimation can be supplied during the development of complex terrain wind farms.