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The Importance of Flapping Kinematic Parameters in the Facilitation of the Different flight Modes of Dragonflies

Journal of Bionic Engineering 2021年第2期18卷 419-427页

作者： Xiaohui Liu Csaba Hefler Wei Shyy Huihe Qiu Department of Mechanical and Aerospace Engineering The Hong Kong University of Science and TechnologyHong Kong SARChina

To better understand dragonflies’remarkable flapping wing aerodynamic performance,we measured the kinematic parameters of the wings in two different flight modes(Normal flight Mode(NFM)and Escape flight Mode(EFM)).When the specimens switched from normal to escape mode the flapping frequency was invariant,but the stroke plane of the wings was more horizontally *** flapping of both wings was adjusted to be more ventral with a change of the pitching angle that resulted in a larger angle of attack during downstroke and smaller during upstroke to affect the flow directions and the added mass ***,the phasing between the fore and hind pair of wings varies between two flight modes,which affects the wing-wing interaction as well as body *** is found that the momentum stream in the wake of EFM is qualitatively different from that in *** change of the stroke plane angle and the varied pitching angle of the wings diverts the momentum downwards,while the smaller flapping amplitude and less phase difference between the wings compresses the momentum *** seems that in order to achieve greater flight maneuverability a flight vehicle needs to actively control positional angle as well as the pitching angle of the flapping wings.

关键词： wing kinematics flight mode dragonfly flight aerodynamics

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AERODYNAMIC FORCE AND FLOW STRUCTURES OF TWO AIRFOILS IN FLAPPING MOTIONS

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Acta Mechanica Sinica 2001年第4期17卷 310-331页

作者：兰世隆孙茂 Institute of Fluid Mechanics Beijing University of Aeronautics & AstronauticsBeijing 100083China

Aerodynamic force and flow structures of two airfoils in a tandem configuration in flapping motions axe studied, by solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between the fore- and aft-airfoil flapping cycles are considered. It is shown that: (1) in the case of no interaction (single airfoil), the time average of the vertical force coefficient over the downstroke is 2.74, which is about 3 times as large as the maximum steady-state lift coefficient of a dragonfly wing; the time average of the horizontal force coefficient is 1.97, which is also large. The reasons for the large force coefficients are the acceleration at the beginning of a stroke, the delayed stall and the 'pitching-up' motion near the end of the stroke. (2) In the cases of two-airfoils, the time-variations of the force and moment coefficients on each airfoil are broadly similar to that of the single airfoil in that the vertical force is mainly produced in downstroke and the horizontal force in upstroke, but very large differences exist due to the interaction. (3) For in-phase stroking, the major differences caused by the interaction are that the vertical force on FA in downstroke is increased and the horizontal force on FA in upstroke decreased. As a result, the magnitude of the resultant force is almost unchanged but it inclines less forward. (4) For counter stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased. As a result, the magnitude of the resultant force is decreased by about 20 percent but its direction is almost unchanged. (5) For 90 degrees -phase-difference stroking, the major differences axe that the vertical force on AA in downstroke and the horizontal force on FA in upstroke axe decreased greatly and the horizontal force on AA in upstroke increased. As a result, the magnitude of the resultant force is decreased by about 28% and it inclines more forward. (6)

关键词： dragonfly flight two airfoils flapping motion Navier-Stokes simulation

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