Spectral partition characteristics of wind turbine load response under different atmospheric stability

Abstract To study the unsteady wind turbine load response under the atmospheric boundary-layer turbulence, we use a measured spectral model from a field experiment to generate atmospheric turbulent flow under different stability and analyze the loads of a full-scale 5 MW wind turbine based on the blade element momentum theory. The results of the spectral analysis show that the measured spectral model has a −1 power law region with higher turbulent kinetic energy relative to other standard spectral models, which indicates an energy-dominant boundary-layer turbulence. By the spectral analysis of the wind-turbine loads, there are three critical frequency: energy-dominant frequency, decoupling frequency and wind-turbine rotation frequency. Below the energy-dominant frequency, power and thrust respond strongly to the energy-dominant boundary-layer turbulence. The modulation effect of the atmospheric boundary-layer turbulence on the unsteady wind-turbine response continues until the decoupling frequency. After that, the power and thrust are mainly influenced by the wind-turbine rotation frequency. The decoupling frequency is strongly correlated with the tip speed ratio, but is weakly influenced by the atmospheric stability. A mathematical model of decoupling frequency and tip speed ratio is also established, which can help to determine the range of turbulence scales that can influence the wind turbine performance.