Lunate-tail swimming propulsion. Part 2. Performance analysis

Karpouzian, G.; Spedding, Geoffrey; Cheng, H. K.

doi:10.1017/s0022112090001318

Cited by 66 publications

(39 citation statements)

References 14 publications

(23 reference statements)

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“…The moderate aspect ratio, three-dimensional foil in Martin et al [80] produced steady and unsteady lift forces comparable to those experienced by the two-dimensional foil employed by Read et al [98]. This demonstrates once more that end-effects are less important in unsteady foils than steady foil, in accordance with the findings in [51], [14], and [25].…”

Section: E Maneuvering Foilssupporting

confidence: 70%

“…The effect of the aspect ratio on the forces is reduced as the reduced frequency increases, because the tip vortices are of alternating sign, hence the induced velocities are significantly reduced. This observation, first made by Karpouzian et al [51], was also reported in the numerical study of Cheng et al [14]. Recent detailed data on three-dimensional foils [80] show little degradation of propulsive performance for moderate aspect ratio foils, compared with the results for two-dimensional foils.…”

Section: B Steadily Oscillating Three-dimensional Foilssupporting

confidence: 69%

“…The tails of some of the fastest swimming animals closely resemble high aspect ratio foils. As a result, flapping foils have been studied extensively using theoretical and numerical techniques [72], [137], [138], [74], [13], [51], [83], [114], [115], [94], [95], and experimentally [109], [17], [68], [6], [98].…”

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confidence: 99%

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Review of Experimental Work in Biomimetic Foils

Triantafyllou

Techet

Hover

2004

IEEE J. Oceanic Eng.

402

196

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Abstract-Significant progress has been made in understanding some of the basic mechanisms of force production and flow manipulation in oscillating foils for underwater use. Biomimetic observations, however, show that there is a lot more to be learned, since many of the functions and details of fish fins remain unexplored.This review focuses primarily on experimental studies on some of the, at least partially understood, mechanisms, which include 1) the formation of streets of vortices around and behind two-and three-dimensional propulsive oscillating foils; 2) the formation of vortical structures around and behind two-and three-dimensional foils used for maneuvering, hovering, or fast-starting; 3) the formation of leading-edge vortices in flapping foils, under steady flapping or transient conditions; 4) the interaction of foils with oncoming, externally generated vorticity; multiple foils, or foils operating near a body or wall.Index Terms-Biomimetics, fish swimming, flapping foil propulsion. I. OVERVIEW OF LITERATURE BIOMIMETIC studies and observations from fish and cetaceans have provided a wealth of information on the kinematics, i.e., how these animals employ their flapping tails and several fins to produce propulsive and maneuvering forces (see reviews in [123] The fluid mechanics and force mechanics of foils have been investigated with the goal of understanding the principles of this different paradigm of propulsion and maneuvering, so as to apply it to enhance existing technology. The tails of some of the fastest swimming animals closely resemble high aspect ratio foils. As a result, flapping foils have been studied extensively using theoretical and numerical techniques [72] II. BASIC PARAMETERS AND DEFINITIONSIn a foil with maximum chord length and maximum span , moving at steady speed , and at an angle of attack , the parameters of relevance are (a) the geometric shape (rectangular, delta-shaped, etc.); (b) the aspect ratio (AR), defined to be equal to the ratio of an average span over an average chord; (c) the angle of attack ; and (d) the Reynolds number , where is the kinematic viscosity of the fluid.

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Section: E Maneuvering Foilssupporting

confidence: 70%

Section: B Steadily Oscillating Three-dimensional Foilssupporting

confidence: 69%

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Review of Experimental Work in Biomimetic Foils

Triantafyllou

Techet

Hover

2004

IEEE J. Oceanic Eng.

402

196

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“…The lunate planform has been shown to be efficient in analytical models of unsteady, low amplitude propulsion (Lighthill, 1970;Cheng and Murillo, 1984;Karpouzian et al, 1990), originally applied to bony fish, sharks, whales and dolphins. The rigidity of the wings may indicate an attempt to maintain this efficient shape in straight and turning flight.…”

Section: Discussionmentioning

confidence: 99%

Vortex wake and flight kinematics of a swift in cruising flight in a wind tunnel

Henningsson

Spedding

Hedenström

2008

Journal of Experimental Biology

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SUMMARY In this paper we describe the flight characteristics of a swift (Apus apus) in cruising flight at three different flight speeds (8.0, 8.4 and 9.2 m s–1) in a low turbulence wind tunnel. The wingbeat kinematics were recorded by high-speed filming and the wake of the bird was visualized by digital particle image velocimetry (DPIV). Certain flight characteristics of the swift differ from those of previously studied species. As the flight speed increases, the angular velocity of the wingbeat remains constant, and so as the wingbeat amplitude increases, the frequency decreases accordingly, as though the flight muscles were contracting at a fixed rate. The wings are also comparatively inflexible and are flexed or retracted rather little during the upstroke. The upstroke is always aerodynamically active and this is reflected in the wake, where shedding of spanwise vorticity occurs throughout the wingbeat. Although the wake superficially resembles those of other birds in cruising flight, with a pair of trailing wingtip vortices connected by spanwise vortices, the continuous shedding of first positive vorticity during the downstroke and then negative vorticity during the upstroke suggests a wing whose circulation is gradually increasing and then decreasing during the wingbeat cycle. The wake (and implied wing aerodynamics)are not well described by discrete vortex loop models, but a new wake-based model, where incremental spanwise and streamwise variations of the wake impulse are integrated over the wingbeat, shows good agreement of the vertical momentum flux with the required weight support. The total drag was also estimated from the wake alone, and the calculated lift:drag ratio of approximately 13 for flapping flight is the highest measured yet for birds.

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“…The maintenance of a small local angle of attack along a flapping wing is analogous to control of the proportional feathering parameter identified by Lighthill (Lighthill, 1969;Lighthill, 1970) for efficient propulsion in oscillating fins, and extended to threedimensional geometries (Karpouzian et al, 1990). In birds, St is allowed to vary with U, so that both f and A can be maintained almost constant.…”

Section: What Fixes the Strouhal Number?mentioning

confidence: 99%

The implications of low-speed fixed-wing aerofoil measurements on the analysis and performance of flapping bird wings

Spedding

Hedenström

McArthur

et al. 2008

Journal of Experimental Biology

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, where Re is a measure of the relative importance of inertia and viscosity) that includes regimes where standard aerofoil performance is difficult to predict, compute or measure, with large performance jumps in response to small changes in geometry or environmental conditions. A comparison of measurements of fixed wing performance as a function of Re, combined with quantitative flow visualisation techniques, shows that, surprisingly, wakes of flapping bird wings at moderate flight speeds admit to certain simplifications where their basic properties can be understood through quasi-steady analysis. Indeed, a commonly cited measure of the relative flapping frequency, or wake unsteadiness, the Strouhal number, is seen to be approximately constant in accordance with a simple requirement for maintaining a moderate local angle of attack on the wing. Together, the measurements imply a fine control of boundary layer separation on the wings, with implications for control strategies and wing shape selection by natural and artificial fliers.

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Lunate-tail swimming propulsion. Part 2. Performance analysis

Cited by 66 publications

References 14 publications

Review of Experimental Work in Biomimetic Foils

Review of Experimental Work in Biomimetic Foils

Vortex wake and flight kinematics of a swift in cruising flight in a wind tunnel

The implications of low-speed fixed-wing aerofoil measurements on the analysis and performance of flapping bird wings

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