Experimental And CFD Simulation Studies Of Flow-Induced Vibration Piezoelectric Energy Harvesting System With Rotation Angles

With the continuous maturity and development of Wireless Sensor Networks(WSNs)technology,its application market prospects in commercial and industrial fields are very expansive.Sensor nodes are usually powered by batteries with limited energy storage,which severely limits the long-term operation of WSNs.Flow-induced vibration piezoelectric energy harvesters are designed to efficiently harvest wind energy from the environment to provide long-term and sustainable power supply for low-power devices,with the advantages of high energy density,simple structure,and long service life.It can effectively meet the power supply requirements of small and low-power devices such as WSNs and Micro Electro Mechanical Systems(MEMS).However,piezoelectric energy harvesters also suffer from low power output due to volume constraints.To improve the energy harvesting efficiency of the energy harvester,this paper designed a multi rotation angles vortex-induced vibration(VIV)-galloping coupling piezoelectric energy harvester,a multi rotation angles square cylinder flowinduced vibration piezoelectric energy harvester,and a circular cylinder flow-induced vibration piezoelectric energy harvester with multi rotation angles splitters.The vibration response and voltage output of the energy harvesters under different wind speeds and different rotation angles were studied through wind tunnel experiments,and then the experimental results were explained from the perspective of internal mechanism through computational fluid dynamics(CFD)simulation.The main conclusions of this paper are as follows:(1)The VIV and galloping of the energy harvester can be activated at the same time with the appropriate design of the cross-sectional shape of the bluff body.The research shows that the VIV-galloping coupling energy harvester can combine the advantages of galloping and VIV,showing a special "hump" phenomenon,resulting in significantly enhanced energy harvesting.Compared with the conventional galloping and VIV energy harvesters,the maximum voltage output of the VIV-galloping coupling energy harvester with “BB1 α = 0°” is increased by 9.8% and 71.34%,respectively.Especially for the "hump" region,the voltage output can be increased by 53.93%compared with the galloping energy harvester.At the same time,it is found that different rotation angles can significantly affect the vibrational behavior of the energy harvester,resulting in different energy harvesting performances despite the same crosssectional shape.(2)By changing the rotation angles of the square cylinder bluff body in the galloping piezoelectric energy harvester,a multi rotation angles square cylinder flowinduced vibration piezoelectric energy harvester can be formed.Studies have shown that the angle of rotation is critical to vibration response and the voltage and power output of the energy harvester.In the range of α = 0° ～ 10°,the energy harvester exhibits galloping,and the energy harvester exhibits the best output power performance whenα = 10°,compared with the conventional galloping energy harvester,the maximum output power is increased by 29.5%.The VIV of the energy harvester occurs in the range of α = 15° ～ 45°,and the optimal rotation angle of the energy harvester in this range is α = 45°.(3)Symmetrical splitters with different rotation angles are installed on the cylindrical bluff body of the VIV energy harvester to form a multi rotation angles splitters piezoelectric energy harvester.Studies have shown that the proper installation position of the splitters plays a key role in increasing the output voltage.The maximum voltage of the conventional VIV energy harvester is limited to 2.37 V.Installing symmetrical splitters with a rotation angle of 60 on the cylindrical bluff body can change the vibration response of the energy harvester from VIV to galloping vibration.For cylinder with symmetrical splitters,the output voltage is increased by 188.61%compared with the VIV energy harvester.CFD simulations found that the combined effect of primary large-scale vortices(PV)and secondary small-scale vortices(SV)plays an important role in the transition from VIV to galloping.