Aerodynamic Performance Analysis Of Four-wing Flapping Aircraft

Flapping-wing aircraft is a kind of bionic aircraft.Unlike traditional fixed-wing and rotorcraft,the flapping-wing aircraft is mainly carried out by flapping,folding and twisting of two wings.It has the characteristics of high flexibility and strong concealment.It is often used in investigation and rescue,and has a good prospect of development.At present,during the research of two-wing flapping aircraft,it is found that the wing layout and motion mode of the two-wing flapping wing aircraft are single,which leads to the stability is not good enough and the lift and thrust can not be produced continuously and efficiently.The four-wing flapping wing aircraft adds a pair of wings and changes the wing layout.By adjusting the motion of the four wings,the stability can be improved effectively,and at the same time,the lift and thrust can be sustained and efficiently generated.Therefore,the research on four-wing flapping aircraft is of great significance.First of all,the wing structure characteristics of four-wing insects and birds are compared,and the flight modes of four-wing insects are summarized.At the same time,according to the basic theory of vortex and the rise mechanism of flapping wing aircraft in flight is summarized,which provides theoretical basis for the definition of the motion equation of two four-wing flapping wing aircraft as follows.Then,two models of four-wing flapping aircraft are proposed,one is the motion model of a dragonfly four-wing flapping aircraft based on the motion of dragonfly,and the other is a motion model of a four-wing flapping aircraft based on the motion mechanism of a bee's wing in flight.The wing deflection movement of the wing about the y-axis is added on the basis of the traditional wing motion model,which makes the trajectory of the airfoil tip change from the original "?" to the "8".A three-dimensional flapping wing model with three motions of "flutter-torsion-deflection" is established,which is closer to the trajectory of the actual bird and insect wings.In order to study the influence of flexible deformation of wing on flapping airfoil conveniently,the flexible deformation of wing is simplified by using approximate flexibility idea.The wing is segmented and the equation of motion is defined respectively,so that the wing has a certain degree of flexibility.Aiming at the disadvantage of traditional flapping area and plane symmetry of fuselage,the lifting force is insufficient.In the newmodel,the initial angle of flutter is added to change the sweep area between the plane of the fuselage and the area below the plane of the fuselage when the wing flutters,so that the moving area of the wing is larger than that of the plane of the fuselage.Increase positive lift.Finally,the four wing flapping wing model is simulated by CFD software.The flutter initial angle,torsion angle,wind speed,flutter frequency,fuselage angle of attack,wing flexibility and wing phase difference are analyzed in detail.The effects of the mean lift coefficient and the average thrust coefficient on the aerodynamic characteristics of the four-wing flapping-wing aircraft are discussed and these laws are theoretically explained.The changes of flow field on the surface of two kinds of four-wing flapping aircraft during the flutter process were observed from the aspects of spanned swirl cloud image,spread velocity cloud image,fuselage hydrostatic cloud image and whole body isovorticity image.The aerodynamic characteristics of two four wing flapping wings are analyzed by using the flow field mechanism,and the flight characteristics of two four wing flapping wings are obtained.