Aerodynamic Characteristics Analysis Of Three-dimensional Dragonfly Wing Flutter Based On Fluid Structure Coupling

The excellent flying ability of dragonflies makes them the most suitable bionic objects for the study of micro flapping-wing vehicles.The dragonfly flaps rapidly and twists its wings while generating an unstable air flow that changes with time.The thrust generated by the interaction with the wings can make the dragonfly fly for a long distance and complete various maneuvering flights.With the continuous development of computational fluid dynamics and the continuous updating of experimental technology and equipment,people can conduct in-depth research on the flight mechanism of dragonflies,and the research on the flight mechanism of dragonflies will play a vital role in the development of new bionic micro air vehicles.This paper takes the dragonfly right front wing with the same outer contour as the object to establish a flat plate model,and uses fluid-structure interaction,overlapping grid technology and computational fluid dynamics method to study the aerodynamic characteristics of the dragonfly flexible wing flapping forward under different conditions.The main research contents of this paper are as follows:Firstly,in order to reveal the unique flight motion mechanism of dragonfly,this paper studies and analyzes the aerodynamic characteristics of dragonfly flexible wing flapping forward flight,and constructs dragonfly front wing with reference to the parameter characteristics of dragonfly front wing.Model.The numerical simulation of the flow field state of the dragonfly front wing flapping was carried out,and the variation characteristics of the lift-drag coefficient of the flexible wing during flapping were obtained under different incoming flow velocities.During flapping,the flexible wing under aerodynamic action will bend and deform in the spanwise direction and passively twist in the chord direction in a flapping cycle.Compared with the rigid wing,the flexible deformation makes the peak value of the lift coefficient increase significantly,and the change of the highly flexible wing lags behind the rigid wing half cycle;the drag coefficient and thrust coefficient are basically unchanged at low incoming velocity,and the maximum thrust coefficient is basically unchanged.The increase was significant,indicating that the flexible wings were significantly helpful for dragonflies to flutter and take off.Secondly,in order to explore the aerodynamic performance of the dragonfly front wing when the flexibility is in flapping forward flight,this paper realizes two different flexibility distributions of the dragonfly front wing by changing the Young’s modulus function of the solid region of the dragonfly front wing.The results show that under the condition of uniform flexibility distribution,the curve of the lift coefficient and drag coefficient of the flexible wing when the Young’s modulus is too small lags behind the half-cycle of the rigid wing and adds drag to the flight,but as the Young’s modulus gradually increases.The increase means that the flexibility gradually decreases,the resistance on the front wing of the dragonfly decreases,the obtained thrust increases,and the momentum increment,acceleration and time-average thrust coefficient that the thrust gives the dragonfly forward flight first increase and then decrease.When flapping forward,the flexible wing with reasonable non-uniform flexible distribution significantly increases the peak thrust coefficient and the time-average thrust coefficient,and gives the dragonfly front wing a larger momentum increment and acceleration.Compared with the rigid wing of the dragonfly front wing with the two flexible distribution methods,the dragonfly front wing can obtain better aerodynamic performance when the flexibility is non-uniformly distributed.In order to explore the change of the aerodynamic performance of the dragonfly front wing under different motion modes,the aerodynamic performance of the two-dimensional dragonfly wing section under different motion modes was first calculated,and it was concluded that in the two-dimensional case,with different flapping planes within a reasonable range With the increase of,the aerodynamic performance will gradually improve;compared with the law of the influence of the flapping plane on the aerodynamic performance,the influence of the degree of freedom on the aerodynamic performance is more complicated than that of different flapping planes.From the preliminary conclusions obtained in the two-dimensional case,the aerodynamic performance of the three-dimensional dragonfly wing under the same flapping plane and different degrees of freedom is calculated,and it is concluded that when the torsion function is a simple harmonic function,the two degrees of freedom in one cycle The aerodynamic performance is better in part of the time period;when the torsion function is a piecewise function,the overall aerodynamic performance of two degrees of freedom in one cycle is significantly better than that of a single degree of freedom.