Investigation On Galloping Piezoelectric Energy Harvester Output Characteristics And Vibration Response Considering Surface Roughness Of Bluff Body

The galloping piezoelectric energy harvester is a device which converts low-velocity water energy from the environment into electrical energy and can serve as an important complement to fluid energy utilization methods.Which consists of cantilever beam,piezoelectric sheet and bluff body.Current research on galloping piezoelectric energy harvesters mainly focuses on changing the bluff body shape to improve the energy harvesting performance and the nonlinearity caused by it,while the influence of bluff body surface roughness on the output characteristics of energy harvesters and the vibration response of bluff body is still unclear.This paper conducts an investigation on the galloping piezoelectric energy harvester in water flow considering the surface roughness of bluff body by mathematical modeling,experimental tests and numerical simulations,and the main work and conclusions are as follows:(1)Based on the extended Hamilton’s principle and Gauss law,the mechanical governing equation and electrical governing equation of galloping piezoelectric energy harvester were established respectively,and the galloping force considering the additional mass of water flow was proposed by the quasi-steady-state assumption,so that the piegewise distributed parameter model of galloping piezoelectric energy harvester considering the flow-solid-electric coupling was established.The analytical solutions of the output voltage,power and onset velocity of energy capturer,and the vibration displacement and frequency of elliptical cylinder were finally obtained by using Galerkin procedure to discretize the displacement of cantilever beam.(2)The experimental system of circulating open channel was established,and the variation of the output power with the elliptical cylinder short diameter and the load resistance were studied by pre-test.The results show that the system had an optimal resistance;the harvester output increased with the decreasing short diameter,and the output power of the elliptical piezoelectric energy harvester with short diameters of 25 mm and 20 mm was 328.88 and 797.77 times that of the cylinder when the flow velocity is 0.6 m/s,respectively.(3)By combining the experimental and model results,the effect of the surface roughness of bluff body on the output characteristics including the output voltage,power and onset velocity of the harvester,and the vibration response including the vibration displacement and vibration frequency of elliptical bluff body was investigated;The significance of the surface roughness of bluff body in the destabilization process was further analyzed,and the effect of surface roughness on the optimal load resistance was studied using the validated mathematical model.The results show that the output power and the amplitude of elliptical bluff body of galloping piezoelectric energy harvester decreased with the increasing surface roughness.The decrease ratio of output power decreased with the increasing flow velocity,while the decrease ratio of amplitude was not affected by velocity.When the flow velocity increased from 0.49 m/s to 0.55 m/s,the decrease ratio of output power corresponding to elliptical cylinder for 20 mm and 25 mm short diameter decreased from 51.8%and 88.1%to 41.5%and 54.5%,respectively;while the decrease ratio of amplitude of both elliptical cylinders was maintained at 22.05%and 31.08%,respectively.Moreover,the increasing surface roughness improves the onset velocity of energy harvester and affected the optimal resistance of system,without changing the vibration frequency of bluff body.(4)The numerical simulation of flow around a elliptical cylinder considering the surface roughness was carried out,to investigate the effect of surface roughness on the flow velocity and pressure in flow field,the vortex shedding from both sides of elliptical bluff body and the lift force acting on bluff body.The results show that the existence of surface roughness reduces the lift force and pressure difference on bluff body,and also reduces the strength and area of the shedding vortex from both sides of elliptical cylinder,which is caused by that the existence of surface roughness reduces the impact of water flow on bluff body,and because of the water viscosity,more water particles are adsorbed on rough surface in the same time,causing the accelerated water flow to slow down,then leading to a negative pressure rise,a reduce of the strength and area of shedding vortex,and eventually resulting in a weakened vibration.The investigation results can provide guidance for structural optimization of piezoelectric energy harvesters operating in natural water flow,and have reference for vibration reduction of large-span flexible devices in flow fields.