Review of the physics of enhancing vortex lift by unsteady excitation

Wu, J.; Vakili, Ahmad

doi:10.1016/0376-0421(91)90001-k

Cited by 74 publications

(29 citation statements)

References 110 publications

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“…However, the other flow mechanisms are totally distinct. The delta wings are static; the sweepback of the wing is the most significant factor responsible for the flow field behaviors, as it allows the incoming flow to have a velocity component along the leading edge, which transports the leading-edge vorticity outward and thus stabilizes the primary vortex of the LEV system (Wu et al, 1991). Unlike the delta wing, flapping wings are highly dynamic; the revolving nature of the flapping motion creates the linear spanwise distribution of the wing speed, which induces the spanwise pressure gradient, centrifugal acceleration and the Coriolis acceleration (Van Den Berg and Ellington, 1997).…”

Section: The Lev Systems On Flapping Wings and Sweepback Fixed Wingsmentioning

confidence: 99%

Three-dimensional flow structures and evolution of the leading-edge vortices on a flapping wing

Yuan

Shen

2008

Journal of Experimental Biology

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SUMMARYFollowing the identification and confirmation of the substructures of the leading-edge vortex (LEV) system on flapping wings, it is apparent that the actual LEV structures could be more complex than had been estimated in previous investigations. In this experimental study, we reveal for the first time the detailed three-dimensional (3-D) flow structures and evolution of the LEVs on a flapping wing in the hovering condition at high Reynolds number (Re=1624). This was accomplished by utilizing an electromechanical model dragonfly wing flapping in a water tank (mid-stroke angle of attack=60°) and applying phase-lock based multi-slice digital stereoscopic particle image velocimetry (DSPIV) to measure the target flow fields at three typical stroke phases: at 0.125T (T=stroke period), when the wing was accelerating; at 0.25T, when the wing had maximum speed; and at 0.375T, when the wing was decelerating. The result shows that the LEV system is a collection of four vortical elements: one primary vortex and three minor vortices, instead of a single conical or tube-like vortex as reported or hypothesized in previous studies. These vortical elements are highly time-dependent in structure and show distinct ʻstay propertiesʼ at different spanwise sections. The spanwise flows are also time-dependent, not only in the velocity magnitude but also in direction.

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Section: The Lev Systems On Flapping Wings and Sweepback Fixed Wingsmentioning

confidence: 99%

Three-dimensional flow structures and evolution of the leading-edge vortices on a flapping wing

Yuan

Shen

2008

Journal of Experimental Biology

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“…Miller and Peskin argue that mean lift, but not drag, produced by a single, isolated wing decreases with decreasing Reynolds number, due to the prolonged attachment of the trailing edge vortex, which they termed 'vortex symmetry'. This effect may be explained by noting that if the leading and trailing edge vortices move together there is no change in the moment of vorticity and thus no lift generated in the direction orthogonal to motion (Wu at al., 1991). This symmetry deteriorates at Reynolds numbers above approximately 32.…”

Section: Vortex Symmetry and Reynolds Number Effectmentioning

confidence: 99%

The aerodynamic effects of wing–wing interaction in flapping insect wings

Lehmann

Sane

Dickinson

2005

Journal of Experimental Biology

177

156

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SUMMARY We employed a dynamically scaled mechanical model of the small fruit fly Drosophila melanogaster (Reynolds number 100–200) to investigate force enhancement due to contralateral wing interactions during stroke reversal (the `clap-and-fling'). The results suggest that lift enhancement during clap-and-fling requires an angular separation between the two wings of no more than 10–12°. Within the limitations of the robotic apparatus, the clap-and-fling augmented total lift production by up to 17%, but depended strongly on stroke kinematics. The time course of the interaction between the wings was quite complex. For example, wing interaction attenuated total force during the initial part of the wing clap, but slightly enhanced force at the end of the clap phase. We measured two temporally transient peaks of both lift and drag enhancement during the fling phase: a prominent peak during the initial phase of the fling motion, which accounts for most of the benefit in lift production, and a smaller peak of force enhancement at the end fling when the wings started to move apart. A detailed digital particle image velocimetry (DPIV) analysis during clap-and-fling showed that the most obvious effect of the bilateral `image' wing on flow occurs during the early phase of the fling, due to a strong fluid influx between the wings as they separate. The DPIV analysis revealed, moreover, that circulation induced by a leading edge vortex (LEV) during the early fling phase was smaller than predicted by inviscid two-dimensional analytical models, whereas circulation of LEV nearly matched the predictions of Weis-Fogh's inviscid model at late fling phase. In addition, the presence of the image wing presumably causes subtle modifications in both the wake capture and viscous forces. Collectively, these effects explain some of the changes in total force and lift production during the fling. Quite surprisingly, the effect of clap-and-fling is not restricted to the dorsal part of the stroke cycle but extends to the beginning of upstroke, suggesting that the presence of the image wing distorts the gross wake structure throughout the stroke cycle.

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“…Our scope is restricted to fluid-dynamical and control issues and, for brevity, we must omit many details. Further information is available in several reviews [2][3][4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Control of vortex shedding on two- and three-dimensional aerofoils

Colonius

Williams

2011

Phil. Trans. R. Soc. A.

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We review and expand on the control of separated flows over flat plates and aerofoils at low Reynolds numbers associated with micro air vehicles. Experimental observations of the steady-state and transient lift response to actuation, and its dependence on the actuator, aerofoil geometry and flow conditions, are discussed and an attempt is made to unify them in terms of their excitation of periodic and transient vortex shedding. We also examine strategies for closed-loop flow and flight control using actuation of leading-edge vortices.

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Review of the physics of enhancing vortex lift by unsteady excitation

Cited by 74 publications

References 110 publications

Three-dimensional flow structures and evolution of the leading-edge vortices on a flapping wing

Three-dimensional flow structures and evolution of the leading-edge vortices on a flapping wing

The aerodynamic effects of wing–wing interaction in flapping insect wings

Control of vortex shedding on two- and three-dimensional aerofoils

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