Investigation Of Aeroelastic Vibration And Harvesting Characteristic Of Airfoil-based Flutter Piezoelectric Energy Harvesters

With the increasing shortage of energy and the extensive application of microelectromechanical system,the traditional chemical battery as an energy source has caused the environmental pollution and required the regular replacement,and the problem of continuous supply energy has become a prominent contradiction.As a potential alternative clean energy source forms,vibration energy harvesters can continuously and stablely supply energy for low-power microelectromechanical system.Energy harvesting technology can transform the vibration energy in the nature into the useful electric energy,therein,vibration sources include wind energy,water energy,mechanical vibration energy,etc.Due to the widespread sources and easy acquisition of wind energy,this paper proposes the airfoil-based flutter piezoelectric energy harvesters for the lower airflow velocity in the nature,which can be applied into aerospace,forest warning,bridge structural monitoring,weather forecasting,etc.,and possesses the important practical significance and widespread application prospect.Based on the working principle of airfoil-based flutter,the airfoil could easily take place the oscillation motion that perpendiculars to the incoming airflow and torsion motion around the elastic shaft.For effectively capturing lower airflow velocity wind energy,a torsion oscillation motions airfoil-based flutter piezoelectric energy harvester is designed.For further decreasing the flutter onset of velocity and improving the harvesting characteristic,a torsion oscillation motions airfoil-based flutter piezoelectric energy harvesters attached with rods and an airfoil oscillation torsion and flap torsion motions airfoil-based flutter piezoelectric energy harvester are designed.The effects of airfoil section shapes and structural parameters of piezoelectric energy harvester on aerodynamic performance and aeroelastic vibration are analyzed,and the optimal airfoil section shapes and structural parameters are obtained.Based on the two dimensional theory of the airfoil and adopting the Hamilton principle,a mathematical model of structure-electric coupled fields of piezoelectric energy harvester is established.Adopting the quasi-steady,unsteady and dynamic stall aerodynamic models,the mathematical model of fluid-structure-electric coupled fields of two degrees of freedom(DOF)torsion oscillation motions airfoil-based flutter piezoelectric energy harvester is derived,and the influences of structural parameters on the aeroelastic vibration and harvesting characteristic are studied.The unsteady aerodynamic model is used to derive the mathematical model of the airfoil-based flutter piezoelectric energy harvester with three DOF airfoil oscillation torsion and flap torsion motions,and the vibration response and harvesting characteristic are studied theoretically.The sensitivity of system output to the stiffness coefficients in airfoil oscillation and torsion DOF is much higher than that of flap torsion DOF.The smaller airfoil torsional stiffness coefficient and the larger airfoil oscillation and flap torsional stiffness coefficient are,the larger aeroelastic vibration response and the better harvesting characteristic can be obtained.The finite element simulation model of multi-physical fields of two DOF airfoilbased flutter piezoelectric energy harvester is established by using the computational fluid dynamics,and the mathematical equation of two DOF motions is derived.The influences of the structural parameters of piezoelectric energy harvester on the flow field characteristics,aeroelastic vibration and harvesting characteristic are numerically analyzed.The coupled effect in oscillation and torsion DOF is explained,and the flow field around the airfoil and harvesting characteristic are obtained.The simulation model of two DOF piezoelectric energy harvesters attached with rods is established,which obtained that the attached rods change the flow field pattern and enhance the aerodynamic performance.The aeroelastic vibration of piezoelectric energy harvester attached with square rod is obviously higher than that of D-shape and without rods.The finite element simulation model of three DOF airfoil-based flutter piezoelectric energy harvester is established,the mathematical equation of three DOF motions is derived,and the effects of the flap installation angles on the flow field characteristics,aeroelastic vibration and harvesting characteristic of the piezoelectric energy harvester are numerically simulated.A decrease of the flap installation angle results in promoting the vortex shedding at the trailing-edge of the airfoil,increasing the aeroelastic vibration,and thus improving the harvesting characteristic.A wind tunnel experimental platform is designed and the experimental prototypes of two DOF airfoil-based flutter piezoelectric energy harvester,two DOF airfoil-based flutter piezoelectric energy harvesters attacted with rods and three DOF airfoil-based flutter piezoelectric energy harvester are fabricated.The effects of the structural parameters and airflow velocity on the aeroelastic vibration and harvesting characteristic are investigated,the effectiveness of two DOF mathematical and simulation models is verified,and the unsteady aerodynamic model can accurately obtain the vibration characteristics and evaluate the harvesting characteristic.It is verified that the piezoelectric energy harvesters attached with square and D-shape rods can reduce the flutter onset of velocity and improve the harvesting characteristic over those without rods.When the airflow velocity is 16.84 m/s,the output voltage and output power of piezoelectric energy harvester attached with square rod can be up to 15.14 V and 0.765 m W,respectively.Comparved with the no attached piezoelectric energy harvester,the enhancement ratios of output power of the piezoelectric energy harvester attached with square rod are all more than 40.5%,and a maximum enhancement ratio is up to 469.7%at 11.1 m/s.The effectiveness of three DOF mathematical and simulation models is verified,and the influences of the flap installation angle on vibration response and harvesting characteristic with three DOF piezoelectric energy harvester are experimentally analyzed.With the decrease of the flap installation angle,the aeroelastic vibration is enhanced and thus the harvesting characteristic is improved.The energy harvesting and vibration suppression can be achieved simultaneously by selecting the appropriate flap installation angle.The energy collecting and storaging circuit is designed.When three DOF piezoelectric energy harvester is charged for 90 s at 16.84 m/s,the capacitor voltage is 1.83 V,and the discharged time for driving the pedometer is up to139 s.