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      Effects of Stroke Deviation on Aerodynamic Force Production of a Flapping Wing

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      AIAA Journal
      American Institute of Aeronautics and Astronautics

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          Abstract

          The effects of stroke deviation of a flapping model insect wing on its aerodynamic force production are studied by solving the Navier–Stokes equations. Stroke deviation of a flapping wing often takes the forms of various out-of-plane wing-tip trajectories that depend on the time variation of the stroke deviation angle. In the present paper, four typical wing-tip trajectories, referred to as cases A–D, were used to investigate the effect of stroke deviation by comparing the aerodynamic forces, flows, and power requirements of the flapping wings with and without stroke deviation. The stroke deviation has remarkable influences on the time course of the aerodynamic force of a flapping wing. The influences could be explained by two mechanisms: one is the added-rotation effect, which is introduced by the deviation angle of the wing; the other is the change in effective angle of attack of the wing, which is due to the angular speed of the deviation. In general, the stroke deviation only produces a small effect on the cycle-mean aerodynamic forces, because the changes due to stroke deviation could be roughly offset in a wingbeat cycle. The analysis of power requirements shows that stroke deviation will generally lead to an increase in energy consumption for insect flights, indicating that insects should have the tendency to maintain the flapping motion in a plane for hovering or low-speed flight, as is observed in nature.

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          Most cited references54

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          Wing rotation and the aerodynamic basis of insect flight.

          The enhanced aerodynamic performance of insects results from an interaction of three distinct yet interactive mechanisms: delayed stall, rotational circulation, and wake capture. Delayed stall functions during the translational portions of the stroke, when the wings sweep through the air with a large angle of attack. In contrast, rotational circulation and wake capture generate aerodynamic forces during stroke reversals, when the wings rapidly rotate and change direction. In addition to contributing to the lift required to keep an insect aloft, these two rotational mechanisms provide a potent means by which the animal can modulate the direction and magnitude of flight forces during steering maneuvers. A comprehensive theory incorporating both translational and rotational mechanisms may explain the diverse patterns of wing motion displayed by different species of insects.
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            Leading-edge vortices in insect flight

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              Spanwise flow and the attachment of the leading-edge vortex on insect wings.

              The flow structure that is largely responsible for the good performance of insect wings has recently been identified as a leading-edge vortex. But because such vortices become detached from a wing in two-dimensional flow, an unknown mechanism must keep them attached to (three-dimensional) flapping wings. The current explanation, analogous to a mechanism operating on delta-wing aircraft, is that spanwise flow through a spiral vortex drains energy from the vortex core. We have tested this hypothesis by systematically mapping the flow generated by a dynamically scaled model insect while simultaneously measuring the resulting aerodynamic forces. Here we report that, at the Reynolds numbers matching the flows relevant for most insects, flapping wings do not generate a spiral vortex akin to that produced by delta-wing aircraft. We also find that limiting spanwise flow with fences and edge baffles does not cause detachment of the leading-edge vortex. The data support an alternative hypothesis-that downward flow induced by tip vortices limits the growth of the leading-edge vortex.
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                Author and article information

                Journal
                aiaaj
                AIAA Journal
                AIAA Journal
                American Institute of Aeronautics and Astronautics
                0001-1452
                1533-385X
                27 October 2017
                January 2018
                : 56
                : 1
                : 25-35
                Affiliations
                Guizhou Normal University , 550025 Guiyang, People’s Republic of China
                Beihang University , 100191 Beijing, People’s Republic of China
                Author notes
                [*]

                School of Mechanical and Electrical Engineering.

                [†]

                School of Energy and Power Engineering; dugang@ 123456buaa.edu.cn . (Corresponding Author).

                [‡]

                Institute of Fluid Mechanics.

                Article
                J055739 J055739
                10.2514/1.J055739
                e10e8df4-72fe-4678-b945-c29bc73590e0
                Copyright © 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. All requests for copying and permission to reprint should be submitted to CCC at www.copyright.com; employ the ISSN 0001-1452 (print) or 1533-385X (online) to initiate your request. See also AIAA Rights and Permissions www.aiaa.org/randp.
                History
                : 1 November 2016
                : 14 June 2017
                : 13 September 2017
                Page count
                Figures: 11, Tables: 1
                Funding
                Funded by: Phd Startup Research Fund Project
                Award ID: 2014
                Funded by: Science & Technology Fund Program of Guizhou Province of China
                Award ID: [2016]1103
                Funded by: National Natural Science Foundation of China10.13039/501100001809
                Award ID: 11572026
                Categories
                Regular Article

                Engineering,Physics,Mechanical engineering,Space Physics
                Engineering, Physics, Mechanical engineering, Space Physics

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