Influence of atmospheric stability on the load spectra of wind turbines at alpha ventus

Abstract

Dependence between fatigue loads on a wind turbine located in an offshore wind farm and atmospheric stability was analysed by using measurement data of alpha ventus. An investigation of the fatigue load spectra of the wind turbines was performed enabling a detailed evaluation besides the damage equivalent load. Therefore, load spectra of a turbine in free-stream and a turbine experiencing wake inflow conditions were compared. Atmospheric stability was taken into account by means of the Bulk Richardson number. It was shown, how atmospheric stability affects load spectra of tower base and blade root bending moment. Hereby, it was found that few events of high fatigue loading increase the damage equivalent load (DEL) substantially, especially in unstable conditions.