Abstract
The interaction between nearby wind turbines in a wind farm modifies the power and loads compared to their stand-alone values. The increased turbulence intensity and the modified turbulence structure at the downstream turbines creates higher fatigue loading, which can be mitigated by wind farm and/or wind turbine control. To alleviate loads and maximize power possible strategies such as wake steering, where the turbine is yawed to redirect the wake such that it does not impinge the downstream turbine, have been studied. The work presented here focuses on situations where the wake is nevertheless affecting the downstream turbine, and more specifically how high loads can be avoided by yawing the wake-affected turbine. The analysis is conducted on a 2.3 MW machine, and the flow field is simulated using the Dynamic Wake Meandering model. The study investigates the impact on power and loads for different longitudinal interspacing and turbulence intensities. Optimal yaw strategies are defined for above rated regions where no power loss occurs. The potential load alleviation for different load sensors are studied, but the presentation is focussed on the blade root flapwise fatigue loading. For full wake at 3D interspacing and turbulence intensity of 5 %, around 35 % of load reduction on the 1 Hz Damage Equivalent Loads can be achieved at high wind speeds. Smaller reductions are achieved for higher atmospheric turbulence; the analogue case with 15 % turbulence intensity shows 17 % potential alleviation. The alleviation on the wind turbine lifetime is also calculated and compared for different turbulence intensities and mean wind speeds. Small reductions are achieved for sites with low mean wind speed and high turbulence intensity, but high reductions, of around 19 %, are accomplished in low turbulence intensity with high mean wind speed.
Highlights
The competitiveness on the wind energy market has pushed the wind turbine industry to develop larger rotors, which yield higher power output
The increased turbulence intensity and the modified turbulence structure at the downstream turbines creates higher fatigue loading, which can be mitigated by wind farm and/or wind turbine control
The lifetime Damage Equivalent Loads (DELs) is presented for the normal operation case, where the wind turbine is aligned with the wind, see table 1
Summary
The competitiveness on the wind energy market has pushed the wind turbine industry to develop larger rotors, which yield higher power output. The control system of the turbine is evolving with the inclusion, for example, of lidar systems. The additional information provided by such sensors has the potential to be used by modern control systems to optimize power and/or reduce the wind turbine loading. Even though the final objective is the same, maximizing power while minimizing loads, different approaches have been presented in the literature. On a single wind turbine, strategies such as individual pitch control for load reduction is studied by [1], where it is demonstrated that a significant reduction in loading can be achieved using relatively straight forward control strategies.
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