Numerical Simulation Of Piezoelectric Energy Capture Device Based On Fluid-structure Interaction

In recent years,piezoelectric energy harvesting has been widely studied as a new type of energy conversion method.In this paper,the phenomenon of periodic shedding Karman vortex street will be formed when the fluid passes through the bluff body.When the shedding vortex street acts on the piezoelectric vibrator,the piezoelectric vibrator will bend and vibrate to generate electricity.In this paper,the effects of Reynolds number,the length of piezoelectric vibrator,the distance between piezoelectric vibrator and bluff body,the shape of bluff body,the stiffness ratio of piezoelectric vibrator substrate to piezoelectric layer,and the mass at the free end of piezoelectric vibrator on the energy capture performance of the device are studied by numerical simulation.Firstly,the natural frequencies and vibration modes of the cantilever beam are studied by theoretical derivation and numerical simulation,and the influence of the fluid environment and the free end mass on its vibration characteristics is studied.It is found that the larger the fluid density is,the larger the resonant frequency of the cantilever decreases;The first three natural frequencies of the cantilever beam also decrease with the increase of the mass attached to the free end,and the first one decreases the most.In addition,the vortex shedding,lift drag coefficient and St number of the flow around the cylinder,semi cylinder,square cylinder and baffle are studied by numerical simulation.It is found that the vortex shedding frequency of the cylinder and semi cylinder is larger than that of the baffle,and the vortex shedding frequency of the square cylinder is the smallest.Before the main research,the accuracy of the two-way fluid structure coupling simulation is verified by comparing the experiments and simulation cases in many literatures.It is found that with the increase of Reynolds number,the maximum open circuit voltage increases,and the maximum amplitude and frequency of the piezoelectric oscillator also increase.In the study of the influence of bluff body shape on energy capture,it is found that under the same Reynolds number and piezoelectric oscillator conditions,the open circuit voltage produced by baffle is the largest,followed by square cylinder.The results show that the vibration frequencies of the piezoelectric vibrator are almost the same under four different bluff bodies: square cylinder,cylinder,semi cylinder and baffle.When the length of the piezoelectric vibrator is from 2 to 8 times of the characteristic size of the bluff body,the maximum open circuit voltage first increases and then decreases.When the length of the piezoelectric vibrator is 4 times of the characteristic size of the bluff body,the maximum output voltage occurs.When the distance between the piezoelectric vibrator and the bluff body is 0 and 1 times of the characteristic size of the bluff body,the piezoelectric vibrator has a large open circuit voltage.When the distance continues to increase,the voltage will gradually decrease.In order to study the influence of the stiffness ratio of substrate to piezoelectric layer on the energy capture characteristics,the piezoelectric oscillator amplitude decreases with the increase of the stiffness ratio,and the maximum open circuit voltage first increases and then decreases with the increase of the stiffness ratio of substrate to piezoelectric layer.In addition,pasting a mass at the free end of the piezoelectric vibrator can effectively improve the energy capture performance such as output voltage.