Negative-Stiffness Torsional-Flutter Energy Harvester under Nonstationary, Moderate-Intensity Winds: New Results

Abstract This work focuses on a wind-based energy harvester that exploits angular vibrations, induced by torsional flutter on an airfoil-shaped object, to produce renewable energy. This device is proposed because of its simplicity and efficiency for installation on a building roof as a complement to other energy systems. There are two main novel aspects compared with previous studies. On one side, the work addresses the technical feasibility of the harvesting device in nonideal, nonstationary flow conditions, which are very common in urban environments with complex building geometry and obstacles. On the other hand, stochastic resonance principles are exploited to induce instability in this nonideal wind condition. Specifically, a negative-stiffness mechanism is embedded within the energy conversion system to enhance the operational performance. Numerical simulations are employed to examine vibrations of the apparatus and its propensity to energy conversion. The intensity of the nonstationary flow field is simulated by multiplying the reference wind speed by a time-varying function that simulates the passage of a sudden gust front. The idea is borrowed from the existing outflow models that are used to describe moderate-intensity thunderstorms. The results demonstrate that the output power of the harvester is low but can still be nonnegligible (about 50 mW) during transient gusty outflows accompanied by moderately high wind velocity (usually above 20 m / s ).