Study On Unsteady Aerodynamic Characteristics Of Bionic Flapping-wing Aircraft

The bionic flapping-wing aircraft is designed to imitate the flight mechanism of birds or insects.The difference between the fixed-wing aircraft and the rotor-wing aircraft is that its power is mainly derived from the flapping-wing motion,which gathers the rise,hover and propulsion in a flapping-wing mechanism to produce upward lift and forward thrust.It is relatively small in size,light in weight,can take off in situ and small site,with good mobility,low energy consumption and high efficiency.This paper makes a comprehensive analysis of the research status of the existing bionic flapping-wing aircraft prototype and its aerodynamics theory at home and abroad.From the aerodynamic characteristics of the aircraft,the wing mechanism modeling and kinematics analysis,numerical calculation analysis and experimental research are carried out.The planar four-link mechanism is used as the flapping-wing mechanism of the aircraft,and the motion equation of the flapping-wing mechanism of the bionic flapping-wing aircraft is established and analyzed according to the geometric relationship of the mechanism,and the wing model is established byusing thin-wing theory and leaf element theory.The computational fluid dynamics(Computational Fluid Dynamics,CFD)simulation is based on the ANSYS fluent software platform,using Navier-Stokes as the main control equation,selecting Spalart-Allmaras turbulence model,and dynamic grid technique.The numerical simulation results of flow field under local air flow condition are obtained by solving the unsteady aerodynamics problem.On this basis,the aerodynamic force and aerodynamic efficiency of the whole wing plane are calculated by numerical calculation.In view of the plunging motion,the study reveals the relationship between different flapping frequency,wind speed parameter,reduction frequency,Reynolds number,flapping amplitude,wing expansion length and flight aerodynamic characteristics,which indicates that reasonable adjustment of parameters plays an important role in the effective flight of bionic flapping-wing aircraft.The numerical simulation of incompressible unsteady flow field is completed for the superposition pitch motion with variable flapping frequency and pitching amplitude.The flow field distribution around airfoil at different times in a period is shown by simulating the motion trajectory in a period.The prototype is manufactured based on the whole mechanism scheme.Due to the limitation of hand-made craftwork,it is necessary for each tested several times to ensure stable flight.The analysis of numerical results in this part provides some reference for the further research of the aircraft.In order to carry on the experimental analysis of the aerodynamiccharacteristics of the bionic flapping-wing aircraft,the test platform is built.Firstly,using static force measuring system,the aerodynamic characteristics with relatively low flapping frequency are studied.The results show that the static thrust of bionic flapping-wing aircraft is increasing with the increasing of flapping frequency,and the frequency spectrum of abnormal frequency fluctuation is analyzed further.Secondly,the aerodynamic characteristics of the attitude sensor with relatively high flapping frequency are studied experimentally.According to the data collected under different conditions,the analysis results show that the space attitude sensor is feasible.