Wind loads on horizontal-axis wind turbines on hilly terrains

Wind loads on wind turbines situated on hilly terrains are substantially different than for wind turbines on flat terrains. The terrain complexity may accordingly affect the fatigue load and service life of wind turbines. It is therefore the scope of the present study to carefully assess aerodynamic characteristics of wind turbines in complex terrain. Wind-tunnel experiments on small-scale models were designed and performed for this purpose. The horizontal-axis wind turbine model was studied because it is the commonly used type of wind turbines in open terrains. The focus was on the size and shape of the hill and the position of the wind turbine relative to the hill. In each case, a single wind-turbine model and a single hill model were concurrently analyzed. The main parameters of interest are the thrust force and the bending moment of the wind-turbine model. The results obtained indicate some important findings. The approach to wind-turbine modeling proved to be accurate and it is recommended for future applications. The effects of hills on wind loads on a wind-turbine model proved to be substantial. Created power is higher for wind turbines placed on a hill. Only twin and large hills channel airflow toward the blades, thus increasing the power coefficient. Compared to the wind turbine with the same rotor hub height situated on the flat terrain, this effect increases the power coefficient by 32% and the thrust force by 13%. The wind thrust force is larger on hilly terrains that yields an increase in the rotor shaft bending and bearing loads, and shorter service life of wind turbines. This effect increases by 18% when the wind turbine is located on a large hill.