Abstract
Wind energy harvesters are emerging as a viable alternative to standard, large horizontal-axis wind turbines. This study continues a recent investigation on the operational features of a torsionalflutter-based apparatus, proposed by the author to extract wind energy. The apparatus is composed of a non-deformable, flapping blade-airfoil. A nonlinear torsional spring mechanism, either simulated by a Duffing model or a hybrid Duffing – van-der-Pol model, installed at equally spaced supports, enables limit-cycle, post-critical vibration. To enhance the output power, stochastic resonance principles are invoked through a novel, negative stiffness mechanism that is coupled to the eddy current device for energy conversion. The output power is explored by numerically solving the stochastic differential equation of the model, accounting for incoming flow turbulence. Three main harvester types with variable configuration are examined; the chord length of the blade-airfoil, used for energy harvesting, varies between 0.5 and 1 m; the spanwise-length-to-chord aspect ratio is four. The flapping frequency varies between 0.10 and 0.25 Hz. The study demonstrates that exploitation of negative stiffness mechanism can improve the performance of the harvester.
