On the relationship between efficiency and wake structure of a batoid-inspired oscillating fin

Dewey, Peter A.; Carriou, Antoine; Smits, Alexander J.

doi:10.1017/jfm.2011.472

Cited by 82 publications

(65 citation statements)

References 35 publications

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“…Third, batoids are increasingly serving as subjects for robotic models of aquatic propulsion (e.g. Blevins and Lauder, 2013;Cloitre et al, 2012;Dewey et al, 2012;Krishnamurthy et al, 2010;Moored et al, 2011a,b;Park et al, 2016), and yet threedimensional biological data on how the wing moves are extremely limited. Such data are needed to provide a template for programming robotic ray wing surface motions, and we aim to provide a new kinematic data set on wing-based aquatic propulsion for this purpose.…”

Section: Introductionmentioning

confidence: 99%

Batoid locomotion: effects of speed on pectoral fin deformation in the little skate, Leucoraja erinacea

Santo

Blevins

Lauder

2017

Journal of Experimental Biology

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Most batoids have a unique swimming mode in which thrust is generated by either oscillating or undulating expanded pectoral fins that form a disc. Only one previous study of the freshwater stingray has quantified three-dimensional motions of the wing, and no comparable data are available for marine batoid species that may differ considerably in their mode of locomotion. Here, we investigate threedimensional kinematics of the pectoral wing of the little skate, Leucoraja erinacea, swimming steadily at two speeds [1 and 2 body lengths (BL) s]. We measured the motion of nine points in three dimensions during wing oscillation and determined that there are significant differences in movement amplitude among wing locations, as well as significant differences as speed increases in body angle, wing beat frequency and speed of the traveling wave on the wing. In addition, we analyzed differences in wing curvature with swimming speed. At 1 BL s −1 , the pectoral wing is convex in shape during the downstroke along the medio-lateral fin midline, but at 2 BL s −1 the pectoral fin at this location cups into the flow, indicating active curvature control and fin stiffening. Wing kinematics of the little skate differed considerably from previous work on the freshwater stingray, which does not show active cupping of the whole fin on the downstroke.

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Section: Introductionmentioning

confidence: 99%

Batoid locomotion: effects of speed on pectoral fin deformation in the little skate, Leucoraja erinacea

Santo

Blevins

Lauder

2017

Journal of Experimental Biology

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“…At high St, after it is shed a vortex is not convected away fast enough to make space for a new one; successively shed vortices are closely spaced leading to dipole formation and jet inclination (Godoy-Diana et al 2009). Analogous to this in case of three-dimensional flows, recently (Dewey, Carriou & Smits 2012) observed the formation of bifurcated jets when the vortex rings self-induce velocities enough to pull the rings away from the centreline of the flow field. For rigid as well as flexible heaving foils, Heathcote & Gursul (2007) find that the inclination angle of the jet reduces with decrease in St (i.e.…”

Section: Introductionmentioning

confidence: 63%

Flexibility in flapping foil suppresses meandering of induced jet in absence of free stream

Shinde

Arakeri

2014

J. Fluid Mech.

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Thrust-generating flapping foils are known to produce jets inclined to the free stream at high Strouhal numbers St = fA/U ∞ , where f is the frequency and A is the amplitude of flapping and U ∞ is the free-stream velocity. Our experiments, in the limiting case of St → ∞ (zero free-stream speed), show that a purely oscillatory pitching motion of a chordwise flexible foil produces a coherent jet composed of a reverse Bénard-Kármán vortex street along the centreline, albeit over a specific range of effective flap stiffnesses. We obtain flexibility by attaching a thin flap to the trailing edge of a rigid NACA0015 foil; length of flap is 0.79 c where c is rigid foil chord length. It is the time-varying deflections of the flexible flap that suppress the meandering found in the jets produced by a pitching rigid foil for zero free-stream condition. Recent experiments (Marais et al., J. Fluid Mech., vol. 710, 2012, p. 659) have also shown that the flexibility increases the St at which non-deflected jets are obtained. Analysing the near-wake vortex dynamics from flow visualization and particle image velocimetry (PIV) measurements, we identify the mechanisms by which flexibility suppresses jet deflection and meandering. A convenient characterization of flap deformation, caused by fluid-flap interaction, is through a non-dimensional 'effective stiffness', EI * = 8 EI/(ρ V 2 TE max s f c 3 f /2), representing the inverse of the flap deflection due to the fluid-dynamic loading; here, EI is the bending stiffness of flap, ρ is fluid density, V TE max is the maximum velocity of rigid foil trailing edge, s f is span and c f is chord length of the flexible flap. By varying the amplitude and frequency of pitching, we obtain a variation in EI * over nearly two orders of magnitude and show that only moderate EI * (0.1 EI * 1) generates a sustained, coherent, orderly jet. Relatively 'stiff' flaps (EI * 1), including the extreme case of no flap, produce meandering jets, whereas highly 'flexible' flaps (EI * 0.1) produce spread-out jets. Obtained from the measured mean velocity fields, we present values of thrust coefficients for the cases for which orderly jets are observed.

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“…In self-propelled cases, the transition from single row to double row wake structure seems to occur as the vortex spacing decreases past a critical value, corresponding with increasing St. We expect that if the ribbon fin swam at higher St, a similar double row wake structure would develop. Other studies of heaving and pitching foils in an imposed flow show that changes in the effective angle of attack also can cause the transition from single row to double row wake structure (Blondeaux et al, 2005;Dewey et al, 2012).…”

Section: Wake Structure In Terms Of St and ηmentioning

confidence: 99%

Undulating fins produce off-axis thrust and flow structures

Neveln

Bale

Bhalla

et al. 2013

Journal of Experimental Biology

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While wake structures of many forms of swimming and flying are well characterized, the wake generated by a freely swimming undulating fin has not yet been analyzed. These elongated fins allow fish to achieve enhanced agility exemplified by the forward, backward and vertical swimming capabilities of knifefish, and also have potential applications in the design of more maneuverable underwater vehicles. We present the flow structure of an undulating robotic fin model using particle image velocimetry to measure fluid velocity fields in the wake. We supplement the experimental robotic work with highfidelity computational fluid dynamics, simulating the hydrodynamics of both a virtual fish, whose fin kinematics and fin plus body morphology are measured from a freely swimming knifefish, and a virtual rendering of our robot. Our results indicate that a series of linked vortex tubes is shed off the long edge of the fin as the undulatory wave travels lengthwise along the fin. A jet at an oblique angle to the fin is associated with the successive vortex tubes, propelling the fish forward. The vortex structure bears similarity to the linked vortex ring structure trailing the oscillating caudal fin of a carangiform swimmer, though the vortex rings are distorted because of the undulatory kinematics of the elongated fin.

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On the relationship between efficiency and wake structure of a batoid-inspired oscillating fin

Cited by 82 publications

References 35 publications

Batoid locomotion: effects of speed on pectoral fin deformation in the little skate, Leucoraja erinacea

Batoid locomotion: effects of speed on pectoral fin deformation in the little skate, Leucoraja erinacea

Flexibility in flapping foil suppresses meandering of induced jet in absence of free stream

Undulating fins produce off-axis thrust and flow structures

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