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

Abstract

When air passes through the wind turbine, the airflow is purely non-homogenous, unsteady and turbulent. The wind speed is critical in the design of wind turbine blades and its support structures. The function of the inner core is to support the rotor blade 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, I-beam, circular and oval-shaped beams. Structural steel, stainless steel 304, aluminium 2014-t6, aluminium 6061-t6, aluminium 7071-t6, aluminium/silicon carbide and cast iron were considered. The 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 by using the S-N curve. When the rotor blades rotate, it experiences load variation due to changes in 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's diagram.
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