Application Of Metasurface Bluff Body Structure In Flow-induced Vibration Energy Harvesting

To meet the self-power supply requirements of micro and small low-power devices such as wireless sensor networks,micro-electro-mechanical-systems and embedded monitoring systems,which are widely used in modern production and life,and solve the problems of limited energy density of traditional batteries and harmful to the environment,the collection of clean energy by flow-induced vibration piezoelectric energy harvester（FIVPEH）has become a current research hotspot.However,the energy harvesting efficiency of traditional FIVPEH still needs to be improved.According to the above research background,this paper introduces metasurface structure and quasi metasurface structure to improve the energy harvesting efficiency of FIVPEH based on the idea of topology and the concept of metasurface.In this paper,three-dimensional CFD simulation technology and theoretical solution model are combined to realize the modeling and calculation of FIVPEH system based on unconventional bluff body,which can accurately identify the aerodynamic parameters of unconventional bluff body.Firstly,according to the lumped parameter method and Kirchhoff current law,the theoretical models of vortex-induced vibration and galloping piezoelectric energy harvester are established,respectively.Then,the theoretical models are verified by wind tunnel experiments,and the effects of different metasurface structures and quasi metasurface structures on FIVPEH are discussed in detail.Furthermore,the vortex shedding processes are simulated to give further insights into the wake oscillating motions.Finally,based on the verified theoretical model,parametric analysis is carried out.The research work and main conclusions of this paper are as follows:（1）Four kinds of metasurface structures,namely,convex hemisphere,convex tri-prism,convex cylinder and convex prism are applied to the vortex-induced vibration piezoelectric energy harvester.The results show that the convex hemisphere and convex tri-prism metasurface structures can reduce Strouhal number S_t to enhance vortex-induced vibration,while the convex cylinder and convex prism metasurface structures can increase Strouhal number S_t to suppress vortex-induced vibration.Among them,the convex hemisphere metasurface structure has the best effect on promoting the piezoelectric energy harvesting of vortex-induced vibration.Compared with the typical VIVPEH with ordinary cylinder bluff body,the maximum voltage and displacement amplitude of Meta-VIVPEH with convex hemisphere metasurface bluff body are increased by 15.56%and 31.43%,respectively,and the energy harvesting bandwidth is widened by 63.64%.However,the convex prism metasurface structure has the strongest inhibitory effect on vortex-induced vibration.The maximum voltage and displacement amplitude of Meta-VIVPEH with convex prism metasurface bluff body are reduced by 29.42%and 17.98%,respectively.（2）Three kinds of metasurface structures,namely,convex cylinder,convex tri-prism and convex wedge,are applied to galloping piezoelectric energy harvester.The results show that these three metasurface structures can increase cubic coefficient A₃to enhance galloping oscillation.Among them,the convex cylinder metasurface structure has the best effect on promoting the piezoelectric energy harvesting of galloping.Further research shows that when the characteristic width of the convex part of the convex cylinder metasurface bluff body is fixed at 6 mm and the height h is 9 mm,the corresponding Meta-GPEH has the best performance.Compared with the typical GPEH with ordinary cuboid bluff body,the maximum vibration displacement and maximum output voltage amplitude are increased by 26.81%and 26.14%,respectively.（3）Two kinds of quasi metasurface structures,namely,bell-shaped and horn-shaped,are applied to flow-induced vibration piezoelectric energy harvester.The results show that the bell-shaped structure can suppress the vortex-induced vibration,while the horn-shaped structure can change the vibration mode of the bluff body from vortex-induced vibration to galloping,so as to promote the piezoelectric energy harvesting.Among them,compared with the typical VIVPEH,when the height h of the quasi metasurface structure is 12 mm,the maximum vibration displacement and maximum output voltage amplitude of the corresponding Bell-VIVPEH are reduced by83.73%and 85.19%,respectively,while the maximum vibration displacement and maximum output voltage amplitude of the corresponding Horn-GPEH are increased by138.07%and 100.92%,respectively.（4）For vortex-induced vibration and galloping piezoelectric energy harvesters,the output power can be significantly improved by increasing the electromechanical coupling strength and adjusting the resistance load to the optimal value.However,when the electromechanical coupling strength increases to a certain extent,the power output reaches a saturation state,and the coupling strength is very large.Therefore,from the perspective of economic benefits,a piezoelectric element with moderate coupling coefficient should be selected for practical application.