The Mechanism Of High Lift On Insects Flying

With the rapid development of micro nano technology and micro electro mechanical systems(MEMS),people began to design micro air vehicles(MAVs).MAVs has many advantages compared with the conventional aircraft and have an extremely broad application in military and civilian field.Although the MAVs has made considerable progress,but there is still a long way to go in practical application.As a new type of aircraft,MAVs face many unique challenges,as its structure,aerodynamic mechanism,flight mode,control methods have a great change.Insects and MAVs are fly in the same Reynolds number domain.Insects obtained good flight skills in range of their flight Reynolds number after a long period of natural selection.They can take full advantage of unsteady aerodynamic mechanism to obtain high lift force.Research into insect flight can help to solve the problems encountered by MAVs in stable and unstable flight conditions.Insects in the free flight need to modulate some flight parameters to deal with various unstable air condition to ensure stable flight and other more complex flight.The flexible deformation of the flapping wing has important influence on the aerodynamic characteristics of the flapping wing.However,the comprehensive of the basic aerodynamic mechanism of flexible deformation is still not clear.This paper numerically simulated the flapping wing by using the dynamic mesh method in the computational fluid dynamics software fluent.Studied the influence of flapping wing's translation amplitude,rotation amplitude,flapping frequency and flexible deformation on lift and drag force.Obtain the lift-coefficient and drag-coefficient and vorticity distribution of the flapping wing under three different conditions,and analyze the aerodynamic characteristics and the variation of flow field.The velocity vector of several typical moments under different flexible deformations are presented.Study about the influence of flapping-wing's translation amplitude,rotation amplitude and flapping frequency shows: the flapping wing's translational amplitude can affect the amplitude of leading edge vortex?trailing edge vortex and wake.Increasing the translational amplitude of the flapping wing can effectively increase lift force and improve the aerodynamic characteristics of the flapping wing.The symmetrical rotation amplitude variations have little effect on lift force or drag force.Change the flapping frequency can greatly change the amplitude of leading edge vortex,trailing edge vortex and wake and greatly increased the pressure difference on flapping wing upper and lower surface.Increasing the flapping frequency can effectively increase lift force.It is found that the chordwise deformation of flapping-wing can change the peak value of instantaneous lift coefficient,but it has little effect on the drag coefficient.The results show that moderate chordwise deformation can increase instantaneous lift force and obtain a large lift force,but excessive chordwise deformation will lead to a decrease of instantaneous lift force,which will adversely affect the aerodynamic characteristics of flapping-wing flight.