Abstract Summary
The recent increasing demand for electricity and renewable energy has encouraged the use of innovative wind-based methods for power extraction. Both macroscale systems (several hundred meters in scale), i.e., large onshore and offshore wind turbines, and micro-scale energy harvesters (few centimeters in scale) used for self-recharging sensors have been widely investigated in the literature. On the contrary, meso-scale devices at intermediate scales (few meters), are still an uncharted research and technology solution. This type of devices has promising potential for growth and innovation. This paper investigates the energy production of a meso-scale, wind-based energy harvester that exploits the torsional aeroelastic instability of a blade-airfoil. Torsional flutter is a single mode aeroelastic instability phenomenon, in which diverging angular vibration of a body occurs. The apparatus relies on a simple mechanism that uses pitch motion generated by fluid structure interaction to extract and convert airflow kinetic energy to electrical energy. The system is composed by a rigid blade-airfoil, connected to a support structure through a non-linear restoring force (spring-like) mechanism that enables the rotation about a reference axis. The proposed technology is designed to be efficient in the range of low and medium wind speeds (10-13 m/s) where, for example, horizontal-axis wind turbines and other harvesters are not efficient. Deterministic pre-flutter, incipient flutter and post critical vibrations of the apparatus have been already explored in a previous study. This work aims to further investigate the aeroelastic behavior of the system by examining the effect of turbulence, random experimental error and modeling simplifications of the aeroelastic forces at incipient flutter of the “flapping foil”. The analysis is conducted in the frequency domain using classical unsteady force models. Monte Carlo methods are explored to solve for the probability of incipient flutter speed. Several configurations with different position of the center of rotation are considered to improve the efficiency of the energy harvester.
