Flowfield measurements in the wake of a robotic lamprey

Hultmark, Marcus; Leftwich, Megan C.; Smits, Alexander J.

doi:10.1007/978-3-642-11633-9_5

Cited by 16 publications

(47 citation statements)

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“…Instead of convecting downstream as a cohesive element, only these small vortices are present in the wake. Their similar strengths and uniform (Fig.9) [after Hultmark et al (Hultmark et al, 2007)]. Unlike in the present study, the tail flexes substantially but actively, and does not deform appreciably in response to fluid forces.…”

Section: Wake Structuresupporting

confidence: 74%

“…For all but the resonant frequency experiment, the frequency was constant at 0.56Hz. This Strouhal number is higher than that of the silver lamprey in steady swimming, which is close to 0.35 (Hultmark et al, 2007).…”

Section: Methodsmentioning

confidence: 48%

“…The robot was adapted from that used by Hultmark et al (Hultmark et al, 2007) and Leftwich and Smits (Leftwich and Smits, 2011) by replacing the original stiff tail with a custom-made flexible tail. Fig.1 shows the entire robot with the padding, waterproof skin and tail removed.…”

Section: Methodsmentioning

confidence: 99%

“…Further details of the robot construction, operation and kinematics can be found in Hultmark et al (Hultmark et al, 2007) and Leftwich and Smits (Leftwich and Smits, 2011).…”

Section: Methodsmentioning

confidence: 99%

“…We investigated of the role of tail flexibility in anguilliform swimming using the robotic lamprey described by Hultmark et al (Hultmark et al, 2007) and Leftwich and Smits (Leftwich and Smits, 2011). The stiff, actively controlled tail used in these earlier studies was replaced by a passively flexible tail with a morphology modeled on computer tomography (CT) scans of the silver lamprey.…”

Section: Introductionmentioning

confidence: 99%

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Wake structures behind a swimming robotic lamprey with a passively flexible tail

Leftwich

Tytell

Cohen

et al. 2012

Journal of Experimental Biology

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SUMMARYA robotic lamprey, based on the silver lamprey, Ichthyomyzon unicuspis, was used to investigate the influence of passive tail flexibility on the wake structure and thrust production during anguilliform swimming. A programmable microcomputer actuated 11 servomotors that produce a traveling wave along the length of the lamprey body. The waveform was based on kinematic studies of living lamprey, and the shape of the tail was taken from a computer tomography scan of the silver lamprey. The tail was constructed of flexible PVC gel, and nylon inserts were used to change its degree of flexibility. Particle image velocimetry measurements using three different levels of passive flexibility show that the large-scale structure of the wake is dominated by the formation of two pairs of vortices per shedding cycle, as seen in the case of a tail that flexed actively according to a predefined kinematic pattern, and did not bend in response to fluid forces. When the tail is passively flexible, however, the large structures are composed of a number of smaller vortices, and the wake loses coherence as the degree of flexibility increases. Momentum balance calculations indicate that, at a given tailbeat frequency, increasing the tail flexibility yields less net force, but changing the cycle frequency to match the resonant frequency of the tail increases the force production.

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Section: Wake Structuresupporting

confidence: 74%

Section: Methodsmentioning

confidence: 48%

Section: Methodsmentioning

confidence: 99%

“…Further details of the robot construction, operation and kinematics can be found in Hultmark et al (Hultmark et al, 2007) and Leftwich and Smits (Leftwich and Smits, 2011).…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Wake structures behind a swimming robotic lamprey with a passively flexible tail

Leftwich

Tytell

Cohen

et al. 2012

Journal of Experimental Biology

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The unsteady three-dimensional wake produced by a trapezoidal pitching panel

2011

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Particle image velocimetry (PIV) is used to investigate the three-dimensional wakes of rigid pitching panels with a trapezoidal geometry, chosen to model idealized fish caudal fins. Experiments are performed for Strouhal numbers from 0.17 to 0.56 for two different trailing edge pitching amplitudes. A Lagrangian coherent structure (LCS) analysis is employed to investigate the formation and evolution of the panel wake. A classic reverse von Kármán vortex street pattern is observed along the mid-span of the near wake, but the vortices realign and exhibit strong interactions near the spanwise edges of the wake. At higher Strouhal numbers, the complexity of the wake increases downstream of the trailing edge as the spanwise vortices spread transversely and lose coherence as the wake splits. This wake transition is shown to correspond to a qualitative change in the LCS pattern surrounding each vortex core, and can be identified as a quantitative event that is not dependent on arbitrary threshold levels. The location of this transition is observed to depend on both the pitching amplitude and free stream velocity, but is not constant for a fixed Strouhal number. On the panel surface, the trapezoidal planform geometry is observed to create additional vortices along the swept edges that retain coherence for low Strouhal numbers or high sweep angles. These additional swept-edge structures are conjectured to add to the complex three-dimensional flow near the tips of the panel.

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Scaling the propulsive performance of heaving flexible panels

2013

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We present an experimental investigation of flexible panels actuated with heave oscillations at their leading edge. Results are presented from kinematic video analysis, particle image velocimetry, and direct force measurements. Both the trailing edge amplitude and the mode shapes of the panel are found to scale with dimensionless parameters originating from the Euler–Bernoulli beam equation. The time-averaged net thrust increases with heaving frequency, but experiences localized boosts near resonant frequencies where the trailing edge amplitude is maximized. These boosts correspond to local maxima in the propulsive efficiency. For a constant heave amplitude, the time-averaged net thrust coefficient is shown to be a function of Strouhal number over a wide range of conditions. It appears, therefore, that self-propelled swimming (zero net thrust) only occurs over a small range of Strouhal numbers. Under these near-constant Strouhal number conditions, the propulsive economy increases with higher flexibilities and slower swimming speeds.

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Flowfield measurements in the wake of a robotic lamprey

Cited by 16 publications

References 0 publications

Wake structures behind a swimming robotic lamprey with a passively flexible tail

Wake structures behind a swimming robotic lamprey with a passively flexible tail

The unsteady three-dimensional wake produced by a trapezoidal pitching panel

Scaling the propulsive performance of heaving flexible panels

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