The Influence Of Structural Parameters And Body Movement On The Performance Of Flapping Wing

Flapping-wing Micro Air Vehicle(FMAV)has great potential for development in terms of flight efficiency,maneuverability,and bionic concealment,and is one of the best choices for carrying out reconnaissance and monitoring tasks in the future.At present,FMAV has low aerodynamic efficiency and can still not fly as efficiently as the flying creatures in nature.One of the main reasons is the lack of high-precision aerodynamic calculation method accounting for complex and flexible structures and the influence of the body movement,which results in inability to design efficient flapping wing.In response to above challenges,the dissertation firstly develops two kinds of aerodynamic calculation method for flexible flapping wing based on measured structural parameters: CFD/CSD and PFSI.Based on CFD/CSD method,the design method of low-power-required flexible flapping wing is developed.In order to study the influence of body movement on flapping flight,a calculation method coupled CFD/CSD with rigid body dynamics is developed and a calculation method coupled PFSI with multi body dynamics is developed which can more accurately model the movement of body and flapping wing.Above methods are validated by high speed camera experiment,wind tunnel experiment and flight test.In addition,the structural optimization design of the flapping wing with both flapping and gliding ability is carried out based on the CFD/CSD and method of surrogate-based optimization.The effect of the flexibility of the flapping wing and the movement of the body on the longitudinal stability are also studied.The detailed contents and conclusions are presented below.(1)Two kinds of aerodynamic calculation method for flexible flapping wing is developed based on measured structural parameters.One is realized by loosely coupling the computational fluid dynamics(CFD)solver with the computational structural dynamics(CSD)software ABAQUS with higher computational accuracy but higher computational cost;The other coupling method is realized by tightly coupling two-dimensional incompressible unsteady airfoil theory with the structural dynamics equation of the flapping wing.In the process of modeling the complex flexible flapping wing structure,this method measures and validates the structural parameters through structural static loading experiments,structural modal measurement experiments and high-speed camera experiments,which fully guarantees accuracy of structural modeling.In terms of aerodynamic calculation,in order to meet different computational requirements,two coupling methods between aerodynamic and structure are developed with different computational accuracy and computational costs.The calculated results are in good agreement with the experimental results,which verifies the accuracy of the calculation method.(2)The design method of low-power-required flexible flapping wing is developed.According to the relationship between the aircraft trim state and the power required for flapping wings,the design goal of the low-power-required flapping wing is determined.Then,several schemes for improving the static thrust and static propulsion efficiency by increasing the ratio of the flapping frequency to the structural modal frequency(frequency ratio)are studied.It is found that the modification of diameter and cross sectional parameters of the carbon rods at the outer side of the flapping wing does not work.Then the effect of the mass distribution of carbon rod on the aerodynamic performance is carried out.By changing the mass distribution of outer rod,the ratio between the flapping frequency and modal frequency is increased,so that the static thrust and static thrust efficiency can be increased at large scale at the same time.Through CFD / CSD computational method,the mass distribution of outer carbon rod is determined and the lift and thrust is improved simultaneously.(3)In order to further improve the accuracy of the calculation method,this paper considers the influence of body movement on the aerodynamic characteristics of flapping wings.Firstly,a coupling method of CFD/CSD/Eo RBD(equation of single rigid body)is developed,and the influence of the body movement on the aerodynamic characteristics of flapping wing flight is studied.The influence of the ratio of the flapping wing mass to the mass of the whole aircraft(referred as mass ratio of flapping wing)on the amplitude of body movement and aerodynamic characteristics is studied.In order to further realize the accurate modeling of inertial force of flapping wing,a coupling method(PFSI/Eo MD)between aerodynamic,structure and flight dynamics based on the multi-body dynamic model is developed.Based on the multi-body dynamic model,the open loop free flight of FMAV is simulated.(4)The newly designed low-power-required flapping wing is tested by flight tests.Three flight tests show that the newly designed flapping wing can save about 13% of power consumption under the same flight speed and flight conditions.Through the acquisition and identification of flight test data,the amplitudes of the flying and pitching movements of the body are obtained and compared with the calculated values.The calculated results are in good agreement with the flight test results,which verifies the correctness of the CFD/CSD/Eo RBD coupling calculation method and achieves the goal of further improving the calculation accuracy for the flapping wing.(5)Based on the CFD/CSD coupling method,the structural optimization design of the flapping wing with both flapping and gliding ability is carried out.Firstly,the flight model suitable for flapping and gliding flight is established based on the assumption that the kinetic energy is unchanged while the potential energy is changed during the whole flight.Based on the surrogate-based optimization using Kriging model,the structural parameters such as elastic modulus and density are optimized.The consuming energy of optimized structure can save more than 30% during flapping and gliding flight theoretically.(6)The longitudinal stability of the flapping wing MAV is systematically studied.The effect of the flexibility of the flapping wing and the movement of the body on the longitudinal stability are studied.The results show that the flexibility of the flapping wing can change the longitudinal stability of the vehicle with rigid flapping wing,which concludes that the flexibility may change the longitudinal stability of the flapping wing in some cases.The effect of body movement on longitudinal stability is studied based on two stability analysis methods.The first method which called averaged method is used to analyze the longitudinal stability of the flapping wing MAV neglecting the movement of the body,while the Floquet method is utilized to analyze the longitudinal stability considering the body's movement.By comparing the corresponding results of the two methods,it is found that the averaged method cannot be applied due to the remarkable movement of the FMAV's body,and it is necessary to use the Floquet method.Based on the pitch damping effect of horizontal tail,a kind of design method for bionic landing gear suitable for FMAV is proposed.