Flow-Induced Instabilities of Scaled Continuous 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 become longer 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 behavior. 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. The flexible airfoil exhibits large-amplitude oscillations and a sub-critical instability for a range of parameters. We also quantify the wind turbine blade displacement and the flow behavior around it as flow-induced instabilities are observed.