Computational and Experimental Study of Flow-Induced Vibration of a Plate/Beam Structure to Improve Performance of Wind Vibration Energy Harvester

Abstract

Wireless microelectromechanical systems (MEMS) are widely used in engineering applications and provide a solution to gather data from remote locations that are not easily accessible. However, traditional power sources like batteries or cables are not always suitable for powering these systems. As a result, the demand of small-scale self-powering systems has increased extensively. Various non-traditional sources of energy have been explored to satisfy the need and researchers have found that the wind-induced flutter in plane structures has great potential to utilize for small scale power generation. However, such developments are still in the laboratory testing stage, as the flutter is a high-velocity phenomenon, compare to that exists at the normal ambient conditions. Despite this, wind-induced flutter has the potential to provide an abundant source of energy for MEMS systems, and further research is warrented to develop and optimize this technology for practical applications. This study explores the unrevealed behavior of flutter of a flag-like structure under the influence of an additional wake field generated by an upstream obstruction. The objective of this research is to enhance the performance of a flutter-based energy harvester under practical ambient flow conditions. A comprehensive experimental investigation is conducted in a wind tunnel setting, and selected numerical simulations are utilized to comprehend the involved flow dynamics. A basic model of a flexible plane structure is considered for the study and its response against the flow under different flow regimes is investigated. Two dimensional numerical simulations including two-way coupling of fluid and structure at low Reynolds number environment are carried out. The primary purpose of the simulations is to understand the effect of additional wake on the modal vibration of a cantilevered structure. The vibration modes are further used to estimate corresponding energy harnessing by correlating induced strain with the piezoelectric transduction mechanism. Additional wake is iv introduced using four different geometries placed upstream: a square, an equilateral triangle, a cylinder, and a D-shape. The results indicate that, for a given flow velocity, different shapes induce different bending mode shapes in the structure. A comparison of energy harnessing with respect to different geometries highlights that the D-shape object yields a higher performance. Several wind tunnel experiments are performed on a laminated plane sheet test geometry under different flow conditions. First, a benchmark study of the flutter of the plane sheet is performed, followed by an investigation of the role of an additional wake from an upstream body. A high speed camera is used to visualize the mode shape of the structure through sequential image processing. The output is analyzed by a frequency spectrum calculated from the time history of the recorded vibration signal. It is found that the critical velocity significantly decreased due to the flow field generated by the upstream bluff body, ranging from 48% to 59%. Regarding different shapes of the body, the D-shape geometry caused the highest reduction in the critical velocity, at 58.19% compared to the benchmark study. To harvest energy, piezoelectric material (MFC) was used, and an output ranging from 0.20 mW to 0.23 mW was observed across an optimum load resistance in different cases. In terms of a nondimensional ratio (ε) of output to input power, a notable increase up to 14 times compared to the benchmark case is recorded from both the aspects of influence on the critical velocity of flutter and energy harnessing under additional wake flow field. The experimental study qualitatively confirmed the conjecture made through the numerical study. The work proposes a proof of concept applicable to all kinds of structures that undergo plane flutter and is beneficial to improve energy harvesting efficiency irrespective of the mode of transduction