Dynamic characterization of a free-freewind turbine blade assembly

Abstract

Accurate prediction of full-field dynamic stress-strain of rotating structures is needed (e.g. wind turbines or helicopter rotors) during operation for condition based monitoring and damage prognosis. In order to perform a dynamic stress-strain prediction of a wind turbine using empirical data, a validated numerical model is required. To understand the dynamic properties and develop a validated finite element model of a 3-bladed wind turbine, an experimental modal test has been conducted and is reported in this paper. Impact hammer modal testing was performed with three wind turbine blades mounted to a hub while supported in a free-free configuration to determine the assembly's resonant frequencies and mode shapes. The results reveal several closely spaced modes present within the turbine assembly. Furthermore, some experimentally derived modes of the multi-blade system can be predicted by determining the modes of an individual blade supported in a cantilevered boundary condition. © The Society for Experimental Mechanics, Inc. 2013.