Investigation On Structural And Aerodynamic Optimization Of Wind-Induced-Vibration Energy Harvester

With the rapid development of the micro-electro-mechanical system and communication technology,multifunctional and low-power micro sensors have been developed significantly.They have essential needs in the fields of transportation,environment,civil engineering,etc.,and have been widely used in environmental monitoring,early fire warning,health monitoring,smart city,and other scenes.At present,the most of micro-electro-mechanical systems use traditional chemical batteries as energy input.However,chemical batteries have limited-service life and result in environmental pollution.Moreover,batteries are hard to be replaced when they are located at bridge tower and the top of high-rise structures.Wind energy widely exists in the natural environment as one of the clean energies.Micro wind-induced vibration energy harvesters convert the wind energy in the working environment into electric energy.Piezoelectric wind energy harvester(WEH)has considerable advantages,such as high energy density,easy processing and integration,and easy miniaturization.Vortex-induced vibration(VIV)and galloping are two crucial types of wind-induced vibrations,which can excite piezoelectric WEH and hence generate power through the piezoelectric effect.Therefore,wind-induced-vibration energy harvester is potential to solve micro-electro-mechanical system and sensors power supply problem.The majority of the existing piezoelectric WEHs are designed based on the ideal wind velocity and specific wind direction.However,the wind velocity and direction in natural wind environments are time-varying and uncontrollable.The variation of wind environment significantly affects the vibration and energy harvesting performance of wind energy harvesters.The VIV-based wind energy harvester is usually sensitive to wind direction and only has a narrow range of working wind velocity.The energy conversion efficiency of wind-induced vibration of galloping-based wind energy harvester needs to be improved.This thesis aims to optimize the structure and aerodynamic shape of the wind-induced vibration energy harvesting system to enhance its energy harvesting efficiency.The main contents of this thesis are follows:1.An omnidirectional piezoelectric wind energy harvester based on VIVs is researched and developed.Based on the self-built wind tunnel test platform,the influences of the combined piezoelectric beam frequency parameters on the vibration and output power of wind energy harvester are analyzed.The performances of piezoelectric VIV-based wind energy harvester with one degree of freedom and that with two degrees of freedom are compared for different wind directions.Compared with the single degree of freedom wind energy harvester with a narrow range of working wind velocity,the omnidirectional wind energy harvester generates abundant power in all wind directions.2.Based on the CFD numerical simulation,the amplitude,output power,aerodynamic force and wake flow characteristics are analyzed.The accuracy of the numerical simulation is verified by comparing with the wind tunnel test results.According to the aerodynamic force and wake flow,the vibration mechanism of the piezoelectric VIV-based wind energy harvester is analyzed.3.The nonlinear magnetic force is applied to the VIV-based wind energy harvester with two degrees of freedom.The theoretical model of the VIV-based energy harvester considering magnetic force has been developed.The accuracy of the theoretical method is verified by the results from wind tunnel test.The lock-in wind velocity range is broadened.The performance of the wind energy harvester is enhanced in the low wind velocity environment.4.The aerodynamic shape of the bluff body at the end of the galloping-based wind energy harvester is optimized.The optimization object is an arc-tail bluff body.According to the tested output power,the Kriging-based surrogate model is constructed,which fits the sampling points well.The surrogate model accurately represents the change of comprehensive output power with aerodynamic shape parameters,improving the accuracy and efficiency of aerodynamic shape optimization.Compared with the prism bluff body wind energy harvester,the output power of the wind energy harvester is doubled by optimizing the aerodynamic shape of the bluff body.The effects of aerodynamic shape modification on the output power,force and flow field are summarized.5.According to the CST parametric method,the geometric characteristics of windward and leeward surfaces are represented.The aerodynamic shape with galloping characteristics is determined.Based on the class function,the aerodynamic shape can be finely described by the shape function.Based on wind tunnel test and numerical simulation,the effects of aerodynamic shape modification on the output power,force and flow field are investigated.The optimal galloping bluff shape is obtained,in terms of the aerodynamic performance.A systematic scheme is formed for galloping aerodynamic shape optimization.The results of bluff body optimization can be extended to the flow induced vibration energy harvesting in ocean and river.