Aerodynamic Analysis And Experimental Investigation Of A Bird-like Flapping-wing Aircraft

The bird-like flapping-wing air vehicle belongs to the bionic field.Its mode of flight is similar to that of birds in nature.It mainly depends on the flapping up and down of wings to generate lift and thrust so as to maintain its flight.The bird-like flapping-wing aircraft has better concealment and flexibility,and is mainly used for reconnaissance and rescue missions.At present,the flapping-wing aircraft transmission mechanism,aerodynamic characteristics and flight control have become the three main aspects of the research.This type of flight has broadened the variety of aircraft.This paper mainly summarizes the previous research achievements and the difficulties and hot spots in the research of flapping-wing air vehicle,and concludes the physiological structure of birds,the mechanism of bird flight and the flight mode of birds.So the paper provides a bionic basis for the definition of the following equation.Traditionally,flapping-wing models are mostly two-dimensional,and it is a whole from the wing root to the wing tip,which is the typical rigid wing.This paper proposes a new three-dimensional flapping-wing model.The wings are divided into inner and outer wings.The inner wing is defined as the rigid wing and the outer wing is defined as the flexibility wing.The multi-section modeling for the wing is carried out by the modeling thought of approximate flexibility,and the flapping angle and pitch angle of each little section wing are defined respectively,and the bending angle is added between the outer wing and the inner wing,so as to establish a three-dimensional flapping-wing model with "flapping-pitching-bending".In view of the shortcomings of Insufficient lift due to complete symmetry on the traditional flapping wings in the process of flapping up and down,the quick-return characteristics is added in the flapping of the new model and the time of flapping down is prolonged so as to prolong the positive lift action time and increase the net lift of flapping wings in a flapping cycle.The CFD fluid software was used to analyze the aerodynamic characteristics of the model.The influence rules of the elevation of the fuselage,flapping frequency,inflow velocity and amplitude of flapping angle on the aerodynamic characteristics of the flapping-wing air vehicle are analyzed in detail from the aspects of lift coefficient,thrustcoefficient,as well as the average lift coefficient and average thrust coefficient and the rules are explained theoretically.From the perspective of the flow cloud image,the flow of the flapping wing is analyzed.The influences of flapping on the flow around the flapping wing are analyzed respectively from the aspects of the spanwise pressure cloud image,spanwise velocity cloud image,the contour vortex map and static pressure cloud images,and the aerodynamic characteristics of the flapping wing is analyzed from the flow cloud image.Then the flow cloud image and the lift coefficient curve are combined to analyze the influence of the flow velocity and the flapping frequency on the flow.Compared with the experiment,a simulation highly similar to the experimental prototype is established,and the influence of the flapping frequency on the aerodynamic characteristics of the simulation is simulated.The three dimensional force sensor,data acquisition card and other equipment are purchased according to the prototype,an experimental platform is set up and data acquisition software is debuged.The actual measurements of lift and thrust of the flapping-wing aircraft are carried out and the influence of flapping frequency on the lift and thrust is carefully analyzed.Besides,the experimental data is compared with the simulation data obtained from the established model.After that,it is found that the rule of the simulation data is roughly similar to the rule of data measured experimentally.Thus the correctness of the simulation model and rationality of the simulation program are verified.