Experimental Observations of Flow-Induced Instabilities in Scaled Flexible Airfoils and Wind Turbine Blades

The study of flow induced instabilities such as flutter has become increasingly relevant in the modern wind turbine blades as they continue to grow longer and slender to achieve higher efficiencies. These designs, while suited for large scale offshore wind energy systems, can result in limit cycle oscillations due to bend-twist coupling resulting in immediate failure of the structure. We present a series of experiments conducted on small scale, non-rotating flexible airfoils with constant cross-section as well as wind turbine blades to observe the onset of flow induced instabilities and post critical behaviour. We maintain the same ratio of flapwise and torsional frequencies as that of the full-scale wind turbine blade using a flexible spine with segments of airfoils attached to it. We discuss the challenges involved with small scale experiments of industrial size wind turbine blades and how they can help inform larger scale experiments in deriving predictive models for these instabilities.