Numerical Study On Aerodynamic Characteristics Of Flapping-wing Air Vehicle In Atmospheric Boundary Layer

Flapping-wing air vehicle is a bionic robot that imitates the flight mode of birds or insects in nature.Among all kinds of Micro Air Vehicles(MAV),flapping-wing air vehicle has many advantages,such as high sensitivity,energy saving,environmental protection and zero-noise,which are favoured by scientists all over the world.At present,the basic principle of flapping-wing air vehicle flight,wing structure and flutter mode simulation are studied deeply at home and abroad.At the same time,some flapping-wing air vehicles that can fly independently have come out,and they are fully noticed by the world.However,most researchers focus their research on the structure of flapping-wing air vehicle,thus ignoring the impact of the external real flow field environment,as a result,these flapping-wing air vehicles only possess fly-ability,but show the weakest point in a slight breeze.Therefore,based on the previous research results and the theory of computational fluid dynamics,the variation of lift and drag coefficients of flapping-wing air vehicle in real working environment,namely in the atmospheric boundary layer is obtained by numerical calculation of its aerodynamic characteristics,which provides a useful reference for further practicality of flapping-wing air vehicle.Based on the flight mechanism of birds and the research of predecessors,the author using the pigeons as the bionic research object,established the wing model and the flapping model according to its size and flight characteristics,and used Adams/View to make wings.The simulation of the wing flapping mechanism obtains the characteristic curve of the wing flapping.The angular velocity equation of the wing flapping is obtained by the discrete Fourier fitting method,which is the basic work for the secondary development of the dynamic mesh.Because the flow field of the atmospheric boundary layer is complex and the calculation domain is large,the traditional dynamic mesh update calculation efficiency is not high when performing the numerical calculation of the aerodynamic characteristics of the flapping-wing air vehicle.To this end,the author will use the sliding mesh in the field of wind turbine research instead of dynamic mesh update,and establish the same flow field environment parameters to calculate the aerodynamic characteristics of the flapping-wing air vehicle.The comparative analysis is based on the sliding mesh and dynamic mesh update.The calculation results of both prove that the sliding mesh has applicability to the study of the aerodynamic characteristics of the flapping-wing air vehicle.On the basis of previous research,based on the SIMPLE algorithm and the RNG k-? turbulence model,the aerodynamic characteristics of the flapping-wing air vehicle in the cruise state are numerically based on the flow field environment in which the flapping-wing air vehicle actually operates in the atmospheric boundary layer.Calculate and obtain the average lift and drag coefficient of the flapping-wing air vehicle.And under the same parameters,the current numerical calculation results in the conventional wind tunnel with the uniform wind profile as the inlet boundary condition are generally compared with the current design stage of the flapping-wing air vehicle.By analyzing the working height,flapping frequency,inlet wind-speed,flapping amplitude,angle of attack and geomorphic conditions on the aerodynamic characteristics of the flapping-wing air vehicle,and the difference in aerodynamic characteristics between the flapping-wing air vehicle in the atmospheric boundary layer and the conventional wind tunnel in the experimental stage is very obvious.Designing a flapping-wing air vehicle for the future has a practical significance that cannot be ignored.