Vortex Induced Vibration (VIV) Based Electro-mechanical Energy Harvesting System in Confined Space

Abstract

The increasing global demand for sustainable and efficient energy sources due to environmental concerns is pressing. Energy harvesting from fluid flows provides a promising option for renewable energy generation, and the development of self-sustaining devices is crucial for practical implementation. In this regard, the need to study the impact of varying the size of bound region on energy harvesting is necessary, which is significant for the optimal design of portable devices due to the establishment of boundary layer. Therefore, this experimental study aims to investigate the effect of changing the distance between wall boundaries on the performance of a piezoelectric-based energy harvester in generating electrical energy from fluid flow. A series of experiments were conducted to analyze the dynamical behavior of a piezoelectric flag due to gap variation and the impact of boundary layer thickness (δ) on its behavior. The setup involved placing inverted C-shaped (120-degree cut) and circular cylinders in a uniform fluid flow, utilizing the undulating motion of the piezo flag in the downstream vortices to harvest electrical energy. The distinct flapping modes were observed in the experimental results which can create varying degrees of coupling in the wake flow. The dynamic behavior of the piezoelectric flag was observed to be influenced by both the gap between cylinder and flag (Dx) and Cylinder to wall (Dy), leading to output power fluctuation. For each 𝑥∗ value, the power output levels were analyzed by experimentally varying Dx values from 1.0 to 5.0 for different values of Dy in terms of δ to find the optimal configuration. The cylindrical arrangement of both bluff bodies, characterized by Dy = 34.05δ and 𝑥∗ = 310 mm, exhibits a persistent pattern of peak power output within the range of 2.0 ≤ Dx ≤ 3.0 due to continuous flapping and significant amplitudes. The inverted C-shaped cylinder (120o cut) shows a maximum gain of 83% in power output compared to the circular cylinder. Furthermore, it is demonstrated that certain spanwise gaps lead to low energy production due to boundary viscous effects and poor coupling of wake flow. This study provides valuable insights into the development of more efficient and optimal sustainable devices for remote practical applications and renewable energy sources, reducing dependence on conventional sources.