Blade Dynamic Response for Downwind Turbines
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A MATLAB script has been developed to investigate dynamics in the blades of a 10 MW downstream wind turbine, with both a tubular- and a truss tower. The classical Beam element momentum method with additional correction factors are used to determine forces on the blade. Centrifugal loading have been applied by use of an iteration method. Blade dynamic response is investigated in terms of Modal analysis. In addition, the dynamic response of a blade with adjusted stiffness has been investigated. Three approaches to obtain the wind velocity field in the rotor plane are studied; averaged Blevins model with input from a study in ANSYS FLUENT, Wind files extracted from ANSYS FLUENT, and results from a small scale wind tunnel experiment. The three cases provide ambiguous results with regards to blade deflection and root flapwise bending moment. Results indicates that vortex shedding have large effect in a tubular tower configuration, but small effect in a truss tower configuration. Based the most the most trusted input, the wind tunnel case, the results indicates that a truss tower would provide more desired values in terms of root flapwise bending moment and fatigue loading.