Impact Testing of a Wind Turbine Blade

The rotor blade diameters of modern wind turbine generators are becoming larger and larger, making manufacturing, transport and installation of wind turbines more difficult than in the past. New challenges also arise with regard to structural dynamics. Therefore it is important to determine the resonance frequencies as early as possible in the design phase. Although design software considers the risk of blade resonance excited by rotating speed, a modal test is the only means to account for structural dynamic deviations from the model. Deviations can result from different influencing parameters during manufacturing and installation.

A team from m+p international was invited by a wind turbine company to do an impact test of a 60 m long wind turbine blade. m+p Analyzer was used to identify the modal parameters. The structure was excited by an impact hammer at various points in the vertical and horizontal direction. m+p VibMobile recorded the related force and accelerations signals.

As expected, the measurements showed the weak damping of the structure. To extract the modal parameters of such kind of weakly damped structures, m+p international improved the widely used Polyreference Time Domain Method (PTD) to Polyreference Least-Squares Complex Exponential Plus algorithm (PTD+). PTD+ can obtain significantly cleaner stabilization charts directly and improve the quality of the results of the modal identification process even for inexperienced users.