Effects Of Flapping Parameters On Asymmetric Flapping Double Wings Of Dragonfly

Flapping-wing is a common flight method adopted by insects in nature.A flapping air vehicle is a new type of aircraft that achieves flight by imitating the flapping wing of insects.It generates lift and thrust at the same time by flapping of wings with advantages of high flight efficiency and good maneuverability.It has broad application prospects in military and civilian applications.However,the currently developed flapping air vehicle is still not practical because of its low aerodynamic lift,poor maneuverability and controllability.The aerodynamic characteristics of flapping wing are the key to stable flight and control of flapping air vehicle.Therefore,it is of great significance to analyze the influence of various flapping parameters on the flight status and aerodynamic characteristics of flapping wing.The dragonflies have always been samples of flapping air vehicle because of their superb flying skills.Experimental observations have found their wings flapping are obviously asymmetrical when climbing or other special flight status.Aiming at aerodynamic characteristics of the asymmetrical flapping,this paper studies the influence of flapping parameters on the aerodynamic characteristics in asymmetrical flapping with numerical simulation method.First,model of the dragonfly is established,then time asymmetry,asymmetry in attack angle and amplitude are simulated,and the downstroke time ratio,attack angle of downstroke,attack angle of upstroke and unilateral amplitude on the time-averaged and instantaneous aerodynamic characteristics,wing surface pressure and vorticity distribution when flapping asymmetrically.The results show that leading edge vortices increase obviously and time average lift is increased with the decrease of the downstroke time ratio.However,time average thrust decreases rapidly and pitching moment increases rapidly.The growth of leading edge vortices are directly affected by angle of attack.Time average lift increases with the increase of downstroke angle of attack,Time average thrust increases with the increase of upstroke angle of attack.The change of unilateral flapping amplitude obviously changes the leading edge vortex size on the wing surface in the downstroke,thus affecting the force and moment in the process of flapping and changing the flying direction of dragonflies.This paper studies the aerodynamic characteristics of asymmetric flapping of compound wings when different flapping parameters change.Deepen the understanding of the aerodynamic characteristics of the flapping wing and provide a theoretical reference for the design of the flapping air vehicle.