Structural Assessment of Wind Turbine Inner Support Based on Confined Wind Conditions Including Fatigue Analysis

Abstract

Naturally when air passes through the wind turbine, the air flow is purely non-homogenous, unsteady and also turbulent. The wind speed is critical in the design of wind turbine blade and its support structures. The function of the inner core is to support the rotor blade for to prevent unwarranted deflection and to lower the vibration of the rotor blade. The inner core beam must be designed to be stiffer and must have moderate weight to allow smooth operation. To achieve the inner core design requirements, four main shapes were considered, namely: Rectangular shape, I-beam shape, Circular shape and finally the oval shaped beam. Structural steel, Stainless steel 304, Aluminium 2014-T6, Aluminium 6061-T6, aluminium 7071-T6, Aluminium/Silicon Carbide and the Cast Iron were considered. Rectangular beam shape was selected due to its minimum tip deflection and low weight. The overall cross section dimension of the beam/ inner core used is 110×260 mm with the thickness of 34 mm. The maximum or tip deflection was found to be approximately 34 mm. Fatigue analysis on the structural steel rectangular beam was analysed using S-N curve. When the rotor blades rotate, it experiences loads variation due to change of wind velocity. After due consideration, It is found that the maximum applied normal stress due to maximum wind velocity did not exceed the endurance limit of the material. Therefore it was concluded that the selected beam shape has infinite life as shown on Goodman diagram.