Optimization of a Vortex-Induced Vibration-Based Energy Harvester by Lock-in Phenomenon Open Access
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This dissertation presents a study of small-scale, vortex-induced vibration-based wind energy harvesting structures consisting of a bluff-body with a piezoelectric-mounted cantilever beam. The purpose of these devices is to harness the significant wind energy existing in the boundary layers around naturally occurring and manmade structures. The rapid variation of pressure and velocity in the boundary layers around these structures can be tapped and used to power structural health monitoring systems or applied to border security sensors that consist of densely populated wireless sensor nodes, offering a reduction in the costs of battery replacement and wiring. The proposed device is a miniature, scalable wind harvesting device. This energy harvesting device couples three different physical domains: fluid, structural and electrical. The configuration consists of a bluff-body with a flexible piezoelectric cantilever attached to the trailing edge. As the cantilever beam vibrates due to shed vortices from the bluff body, the strain energy in its deformation is converted into electrical energy by piezoelectric transduction. This study employs the use of COMSOL multiphysics software using the fluid-structure interaction module for Computational Fluid Dynamics (CFD) modeling and simulations. The results from the CFD modeling are interfaced with MATLAB for further electromechanical simulations. A linearized dynamic mathematical electro-mechanical model of a vibrating cantilever beam associated with energy harvesting is also presented. Simulations are run for different characteristic dimensions, shapes for the bluff body, length-to-diameter ratio, and optimized for maximum power over a wide range of flow velocities. The harvester is optimized by the phenomenon of lock-in. Lock-in is defined to occur when the cantilever oscillates at the same frequency as the undisturbed wake behind the bluff body. The integrated fluid-structure interaction with the piezoelectric module is used to find the different non-dimensionless parameters that are important to study the energy harvesting model for higher efficiencies. The most optimized harvester design from this study, in terms of efficiency and range of lock-in bandwidth, is achieved by the D-shaped bluff body harvester, compared to cylindrical and pentagonal bluff bodies. The average total efficiency of the D-shaped bluff body between the lock-in bandwidth is found to be 0.0037.