Topology Equivalent Aerodynamic Design And Performance Analysis Of Galloping Piezoelectric Energy Harvester

Under the conflict between the use of fossil energy and environmental problems,wind energy is regarded as a universal clean energy because of its advantages of high content,wide distribution,renewable and pollution-free.Moreover,such technologies are developing continuously with the deepening of these problems in the world.As a new type of self-power device,piezoelectric energy harvester can easily convert clean renewable energy(wind energy,hydro-energy,etc.)in the surrounding environment into electricity.Moreover,with the characteristics of long life,small size no regional restrictions and high energy density,this harvester shows significant advantages in the renewable development.In this thesis,the energy conversion part of galloping cantilever piezoelectric wind energy harvester is designed in the respect of aerodynamic performance,and their comparative study is carried out by wind tunnel experiment,numerical simulation and so on.The main research contents are as follows:(1)Aiming at the problem of weak output power of square,the aerodynamic structure design of bluff body is carried out from square to triangle to funnel-shape.The reattachment phenomenon occurred because of the exiting rear side causes the side force fluctuation and even weakens the vibration amplitude.By combining the rear end and properly increasing the size ratio,the vortex shedding can be coordinated and the pressure drag is reduced.On the basis of triangle,the symmetrical points on the both sides near the windward are concave inward to form a funnel shape,so as to achieve the consistency of the direction between side and lift force,meanwhile enhance the structure non-streamline characteristic.(2)Based on galloping cantilever piezoelectric energy harvester,the mechanical and electric governing equations are respectively established through Hamilton's principle and Gauss's law firstly,and the galloping aerodynamic force in the process of vibration is calculated.Galerkin discrete method is introduced to reduce the order of the whole mechanical and electric governing equations.Then the equivalent structure method,which can realize the equal substitution of mechanical effect to electrical effect,is used to decouple and merge the governing equations.Finally,the analytical solutions of the onset speed and output power density of the system are obtained to predict the influence of different parameters on system performance.(3)The performance of the designed bluff bodies is tested by numerical simulation and wind tunnel test,and the mathematical model is verified.It is found by numerical simulation that the lift coefficients of funnel-shape,triangular and square bluff bodies are 6,4,0.8,respectively.It can also be seen from the pressure and velocity counters that the intensity of vortex and the pressure difference on the both sides for funnel-shape bluff body is the largest,followed by triangular,and the square is the smallest.According to the result of wind tunnel experiment,the onset speed of funnel-shape,triangle and square are respectively 7 m/s,9 m/s and 13 m/s.the maximum output power density of funnel-shape bluff body is 2 times of that of triangle and 11 times of that of square.The funnel-shape energy harvester has the characteristics of wider harvesting range,higher output power and more stable system voltage amplitude and frequency,which reveals its best harvesting performance.(4)Because of high agreement between model solution and experimental data,the influence of the external load resistance,the mass and length of bluff body,the thickness of cantilever and system's electrical damping on the onset speed and output power density of the system is analyzed The results show that no matter how the parameters change,the order of superiority and inferior for different energy harvesters always be maintained.Its order of harvesting performance is consistent with the experimental results.Their output power density is respectively nearly 3.9631 mW/cm3,1.8909 mW/cm3 and 0.2203 mW/cm3 under the optimal electric damping.It is also found that the optimal resistance value for different energy harvesters are almost the same.But the change trend of mass and length of bluff body for optimization between onset and power density is opposite,so the trade-off about mass and length of bluff body should be implemented for the design of the optimal harvester.