Effect of leading-edge curvature on the aerodynamics of insect wings

The Lighthill-Weis-Fogh clap-fling-sweep mechanism is a movement used by some insects to improve their flight performance. As first suggested by Lighthill (1973), this mechanism allows large circulations around the wings to be established immediately as they start to move. Initially, the wings are clapped. Then they fling open like a book, and a non-zero circulation is established around each of them. Thus one wing can be considered as the starting vortex for the other. Then they sweep apart, carrying these bound vortices and generating lift. Since the insect wings have relatively low aspect ratio and rotate, 3d effects are important, such as spanwise flow and stabilization of the leading edge vortices (Maxworthy, 2007). To explore these effects, we perform direct numerical simulations of flapping wings, using a pseudo-spectral method with volume penalization. Comparing 2d and 3d simulations for the same setup clarifies the role of the three-dimensionality of the wake. Our results show that the 2d approximation describes very well the flow during fling, when the wings are near, but 3d effects become crucial when the wings move far apart. Possible extensions of the numerical method for modeling the interaction with thin elastic wings using FSI will also be presented.

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The Functional Role of Wing Corrugations in Living Systems

Journal of Fluids Engineering ◽

10.1115/1.3242550 ◽

1986 ◽

Vol 108 (1) ◽

pp. 93-97 ◽

Cited By ~ 22

Author(s):

R. H. Buckholz

Keyword(s):

Reynolds Number ◽

Functional Role ◽

Separated Flow ◽

Leading Edge ◽

Flow Region ◽

Wing Surface ◽

Living Systems ◽

Recirculation Region ◽

Insect Wings

Questions concerning the functional role of spanwise wing corrugation in living systems are experimentally investigated. Attention was initially directed to this problem by observation of the irregular shape of many insect wings as well as other studies indicating higher lift on these wings. First, a flow visualization scheme was used to observe and photograph streamlines around two different wing sections. One of these, a sheet metal model with geometry matching that of a butterfly wing, was studied at a chord Reynolds number of 1500 and at a Reynolds number of 80 based on corrugation depth. A steady-state recirculation region near the model leading edge was found, and the separated flow region above this recirculation zone formed a laminar reattachment to the model. A second thicker wing was corrugated on the upper surface. Closed streamlines inside these upper surface corrugations were photographed at Reynolds numbers of 8000 and 3800 based on chord length, and 200 and 90 based on corrugation depth. Reductions in pressures on the corrugated upper wing surface relative to a smooth upper wing surface were then measured.

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A scaling law for the lift of hovering insects

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.568 ◽

2015 ◽

Vol 782 ◽

pp. 479-490 ◽

Cited By ~ 14

Author(s):

Jeongsu Lee ◽

Haecheon Choi ◽

Ho-Young Kim

Keyword(s):

Scaling Law ◽

Measurement Data ◽

Leading Edge ◽

Micro Air Vehicles ◽

Structure Comparison ◽

Theoretical Understanding ◽

Vortical Structures ◽

Insect Wings ◽

Simple Scaling ◽

Edge Vortex

Insect hovering is one of the most fascinating acrobatic flight modes in nature, and its aerodynamics has been intensively studied, mainly through computational approaches. While the numerical analyses have revealed detailed vortical structures around flapping wings and resulting forces for specific hovering conditions, theoretical understanding of a simple unified mechanism enabling the insects to be airborne is still incomplete. Here, we construct a scaling law for the lift of hovering insects through relatively simple scaling arguments of the strength of the leading edge vortex and the momentum induced by the vortical structure. Comparison of our theory with the measurement data of 35 species of insects confirms that the scaling law captures the essential physics of lift generation of hovering insects. Our results offer a simple yet powerful guideline for biologists who seek the evolutionary direction of the shape and kinematics of insect wings, and for engineers who design flapping-based micro air vehicles.

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The Importance of Torsion in the Design of Insect Wings

Journal of Experimental Biology ◽

10.1242/jeb.140.1.137 ◽

1988 ◽

Vol 140 (1) ◽

pp. 137-160 ◽

Cited By ~ 10

Author(s):

A. ROLAND ENNOS

Keyword(s):

Leading Edge ◽

Mechanical Tests ◽

Inertial Effects ◽

Aerodynamic Forces ◽

Great Resistance ◽

Aerodynamic Efficiency ◽

Insect Wing ◽

Wing Model ◽

Insect Wings ◽

Set Up

A model insect wing is described in which spars of corrugated membrane which incorporate stiffening veins branch serially from a V-section leading edge spar. The mechanical behaviour of this model is analysed. The open, corrugated spars possess great resistance to bending, but are compliant in torsion. Torsion of the leading edge spar will result in torsion and relative movement of the rear spars. As a result camber will automatically be set up in the wing as it twists. Aerodynamic forces produced during the wing strokes will result in torsion and camber of the wing which should improve its aerodynamic efficiency. The effects of varying parameters of the wing model are examined. For given wing torsion, higher camber is given by spars branching from the leading edge at a lower angle, by spars which curve posteriorly, and by spars which diverge from each other. Wings of three species of flies were each subjected to two series of mechanical tests. Application of a force behind the torsional axis caused the wings to twist and to develop camber. Immobilizing basal regions of the leading edge greatly reduced compliance to torsion and camber, as predicted by the theoretical model. Aerodynamic forces produced during a half-stroke are sufficient to produce observed values of torsion and camber, and to maintain changes in pitch caused by inertial effects at stroke reversal.

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Forewings match the formation of leading-edge vortices and dominate aerodynamic force production in revolving insect wings

Bioinspiration & Biomimetics ◽

10.1088/1748-3190/aa94d7 ◽

2017 ◽

Vol 13 (1) ◽

pp. 016009 ◽

Cited By ~ 8

Author(s):

Di Chen ◽

Dmitry Kolomenskiy ◽

Toshiyuki Nakata ◽

Hao Liu

Keyword(s):

Aerodynamic Force ◽

Force Production ◽

Leading Edge ◽

Insect Wings ◽

Leading Edge Vortices

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The aerodynamics of hovering insect flight. IV. Aerodynamic mechanisms

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1984.0052 ◽

1984 ◽

Vol 305 (1122) ◽

pp. 79-113 ◽

Cited By ~ 289

Keyword(s):

Insect Flight ◽

Experimental Studies ◽

Leading Edge ◽

Reynolds Numbers ◽

Recirculating Flow ◽

Insect Wings ◽

Animal Flight ◽

Edge Separation ◽

Theoretical Considerations ◽

Sharp Leading Edge

Theoretical considerations and available experimental studies are combined for a discussion on the aerodynamic mechanisms of lift generation in hovering animal flight. A comparison of steady-state thin-aerofoil theory with measured lift coefficients reveals that leading edge separation bubbles are likely to be a prominent feature in insect flight. Insect wings show a gradual stall that is characteristic for thin profiles at Reynolds numbers (Re) less than about 105. In this type of stall, flow separates at the sharp leading edge and then re-attaches downstream to the upper wing surface, producing a region of limited separation enclosing a recirculating flow. The resulting leading edge bubble enhances the camber and thickness of the thin profile, improving lift at low Re. Some of the results for bird wing profiles indicate that the complications of leading edge bubbles might even be found in the fast forward flight of birds.

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