Research on the Loads of NREL 5MW Wind Turbine under Stable Atmospheric Conditions

To study how the atmospheric turbulence affects the wind turbine, blade element momentum theory coupled with harmony superposition method was used to study the loads of NREL 5MW wind turbine based on the standard Von Karman spectrum and NWTC measured spectra with different atmospheric stability. The results show that the standard Von Karman spectrum overestimates power and thrust relative to NWTC spectrum. From a frequency domain perspective, there is a critical frequency linearly related to the tip speed ratio, which determines the range of turbulence scales that can affect the wind turbine. The wind-turbine loads are mainly affected by the low-frequency turbulent structure in the flow below the critical frequency and decoupled from the flow above the critical frequency. From an intuitive perspective, the low-frequency turbulence structure can't be effectively absorbed by the rotor, but is transformed into fatigue loads by the structure.