Parametric aerodynamic and aeroelastic study of a deformable flag-based energy harvester for powering low energy devices

Abstract

Extensive wind tunnel experiments were performed to find the optimal and most influential parameters for energy harvesting from piezoelectric membranes (thin elastic cantilevered plates), herein called flags. Four different piezoelectric flags were tested in conjunction with the seven different bluff bodies at various wind speeds and streamwise gaps between the bluff body and flag. Stiffness of the flags was also varied along with its length to assess the impact on harvested power. Various flapping modes are observed for different flags which correspond to the amount of harnessed power. The results revealed that altering the stiffness of flag can produce an increase of 29 and 31 times in power generation for long and short flags, respectively. It was found that the 120-degree bluff body produced the largest power with the capability to generate a strong wake region. Further analysis of the best performing flag (short and stiff) for various bluff bodies shows a remarkable increase of 661.2 % in generated power. This membrane shows rhythmic periodic flapping with higher modes of deformation in comparison to its other flag counterparts. These alternate flags show out-of-plane and twisting motion which wastes strain energy and causes a cancelation effect, reducing total energy output. The results show that in designing an efficient and reliable energy harvester, the flag’s stiffness and length as well as the shape of the bluff body play an important role. Furthermore, in comparison with the flutter phenomenon (i.e. a dynamic instability of the flag in the absence of a bluff body), the results with a bluff body demonstrate that higher energy generation can be achieved at a lower wind speed, thus paving the way for small and practical energy harvesting devices specifically in remote areas.