| Wind energy has significant advantages such as wide distribution,abundant storage capacity,sustainability and no pollution.Wind vibration generated by wind flowing through solids has a broad prospect of development and application because of its abundant energy storage.Piezoelectric energy harvesters are widely used for wind vibration energy harvesting because they can convert mechanical vibration energy generated by structures into electrical energy for self-powering of small sensors and microelectromechanical systems.In order to improve the output efficiency and stability of the piezoelectric energy harvester,this paper proposes a new piezoelectric energy harvester with vibration induced by the wake flow of elliptical cylinder,and on the basis of summarizing the current situation of domestic and foreign research,a research scheme of piezoelectric energy harvesting with different aspect ratios of elliptical cylinder wake flow excitation is proposed.The research contents of this paper are as follows:(1)A mathematical model of the wind-induced vibration piezoelectric energy harvester is established.In order to analyze the performance of the energy harvester,the mechanical control equation and electrical control equation are derived based on the Euler-Bernoulli beam theory using the extended Hamiltonian principle and Gauss’s law.The aerodynamic forces generated by a non-stream lined bluff body system during How around are calculated.The model simplification was carried out by the method of electromechanical decoupling,and the approximate analytical expressions of the onset wind speed and output voltage and power were finally obtained.(2)The design of the test experimental setup of the energy harvester was carried out in a closed-ended DC low-speed wind tunnel.The output of the piezoelectric energy harvester withinduced vibration is affected by the wind speed,the shape of the interference cylinder and the bluff body,and the spacing ratio,etc.Therefore,in this paper,four elliptical cylinders with different cross-sectional shapes of the aspect ratio AR=1,0.8,0.6 and 0.4 are selected as the interference cylinder from the viewpoint of aerodynamic design,and a funnel-shaped column is selected as the downstream bluff body.The flow field characteristics were calculated by numerical simulation for the elliptical cylindrical case with different cross-sectional shapes of the upstream interference cylinder,and the lift forces were monitored.The comparison is used to test the correctness of the parameter selection.(3)The effects of different wind speeds and different spacing ratio on the performance of the energy harvester under four different cross-sectional shapes of elliptical cylindrical wake were tested,and the proposed model was verified.The experimental results show that the prediction curves of the model match with the experimental results.From the output data,the bluff body has an obvious induced galloping phenomenon.According to the variation law of the output power with the aspect ratio,the distance between the interference cylinder and the bluff body is clearly divided into three different fluid regions:the proximity interference region,the induced galloping region and the wake interference region,in which the maximum output power of the energy harvester is located in the induced galloping region.The maximum output power densities under wake excitation of the four types of interference cylinder are 4752 W/m~3,4182 W/m~3,7190 W/m~3,and 10930 W/m~3,The output power of the elliptical cylindrical wake with AR=0.4 is 2.3 times higher than that of the cylindrical wake.As a result,the output power of the bluff body with elliptical cylindrical is significantly higher compared to the case with cylindrical and the system has a higher output power density and better acquisition performance as the aspect ratio decreases.(4)The vibration stability of the system was analyzed by means of Phase portraits and the variation coefficient for maximum amplitude of variation curves.The results show that not only the output power is higher the induced galloping region and in the case of the smaller the aspect ratio,but also the vibration stability of the bluff body is better at this time.The experimental parameters were optimized by the verified mathematical model,and the effects of different external load resistances on the energy output power density,and the effects of the width of the windward side of the bluff body on the aerodynamic force were analyzed and compared.The results show that at larger wind speeds,the piezoelectric energy harvester under the influence of the elliptical cylinder(0<AR<1)wake has a strong tendency to vary under the influence of resistance compared to the cylindrical one(AR=1),and the aerodynamic force on the downstream bluff body tends to increase as the width of the flow projection plane.This result provides a theoretical basis for the selection of the optimal resistance value and the width of the flow projection plane of the bluff body. |
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