Reserch On Flight Mechanisms Of Honeybees Based On Wind Tunnel Experiments

The Micro Aerial Vehicle (MAV), which can fulfil tasks that the normal aircraft cannot perform in the complex topography and bad environment, has a series of advantages,such as smaller volume, lower power dissipation and higher maneuverability, and can bewidely applied to military reconnaissance, aerial photograph and environmental monitoring.Consequently, flapping flight has important theoretical value and application prospect.Honeybee is chosen for the study object of the paper, and the flapping flight mechanisms ofhoneybees have been systematically studied with wind tunnel experiments and numericalsimulations. Main works are as follows:(1) Low-speed wind tunnel used for flow field visualization of insects had beendesigned and manufactured. In order to improve the flow field quality of wind tunnel, theoptimum sizes of test section, diffuser section and contraction section of wind tunnelaccording to characteristics of flow field were researched and determined, while witozinskycurve selected as contraction curve. Honeycombs and nylon screens were added in settlingchamber and power section of wind tunnel to reduce turbulence intensity and ensure flowsteady. The designed smoke device was installed in the tunnel, and high-speed cameras andlights were arranged reasonably, thus developing an intact experimental system of flowfield visualization.(2) Flow field visualization experiments of honeybees flapping were conducted by thelow-speed smoke wind tunnel. With the help of model established and imagessynchronously shot by two high-speed cameras, characteristics of wing flapping wereobtained, including flow field structures of far field and near field. Vortex evolution ofhoneybees’ flapping flight was researched, and influence of wake vortices on inducedvelocity was qualitatively analyzed. The flow visualization experiment showed that:continuous vortex wakes of wing tip formed vortex tube during downstroke; downstrokestop vortex and upstroke starting vortex were generated during supination; vorticitydirections of forewing and hindwing was opposite caused by the deformation along thechord; and leading edge vortex was the most obvious and the size of leading edge vortex was increasing from wing root to tip at the end of downstroke. During the end ofdownstroke there was a vortex wing, which was composed of the leading vortices along thespan, wake vortex tube of wing tip vortices, and wing root vortices wake, on left and rightwing respectively. Vortex ring lift estimated was larger than the weight of honeybee,suggesting that lift generated by wing flapping can support honeybee to fly with some extraweight.(3) A honeybee model and its coordinate system were established, with kinematicequations of the model wing provided based on the regular patterns of honeybees’ flappingwing. The flow field of honeybee flapping was solved by dynamic mesh technique. Resultsof post processing of flow field indicated that leading edge vortex, wing tip vortex, wingroot vortex and trailing edge vortex appeared on wings. Numerical simulation resultsverified the conclusions of wind tunnel experiment that: at the end of downstroke, the sizeof leading edge vortex was increasing from wing root to tip and leading edge vortex metwing tip vortex; at the end of downstroke, downstroke stop vortex appeared at the trailingedge, which would decrease the lift, while at the beginning of upstroke, upstroke startingvortex at trailing edge increaseed the lift; on left (right) wing, wing tip vortex wakes, wingroot vortex wakes and wing surface vorticity constituted the intact vortex ring which wascircular. The numerical simulation results still indicated that wing rotation made the size ofleading edge vortex maximum at the end of upstroke (downstroke), and at the end ofupstroke wing tip vortex wake, wing root vortex wake and wing boundary vortex met toform the Ear-like vortex ring. In the centers of the upstroke and downstroke vortex ring, thedownward jet vertical to the vortex ring plane appeared.(4) According to the wing entities of honeybee, the coordinate system of honeybeewing model was established to define lift, thrust, aerodynamic power and inertial power.Aerodynamics and powers of single-wing model, double-wing model and integral of thehoneybee model were compared through numerical simulations, indicating that theinteraction effects of aerodynamic characteristics on single wing can be neglected.Meanwhile, through altering working conditions, such as frequency, maximum flappingangle, mid-stroke attack angle，reverse timing and position of rotation axis, the varyingpattern of aerodynamic forces and power of the single wing model were obtained by simulations. Current work aims to make contribution to research and manufacturing of thebio-inspired micro flapping-wing aerial vehicle.