Effect of the stiffness, inertia and oscillation kinematics on the thrust generation and efficiency of an oscillating-foil propulsion system

Richards, Andrew J.; Oshkai, Peter

doi:10.1016/j.jfluidstructs.2015.07.003

Cited by 16 publications

(9 citation statements)

References 21 publications

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“…To make it visible, the time variation of the thrust coefficient of f * = 0.17 was locally amplified, as shown in Figure 9a. Therefore, it is evident that the reduced frequency has a significant effect on the propulsion performance of the flapping hydrofoil, and the same conclusion can be found in [41,42]. We also note that there is a phase difference between the evolution of the thrust coefficient for f * = 0.17 and f * = 0.68.…”

Section: The Influence Of the Reduced Frequencysupporting

confidence: 78%

Numerical Investigation of the Semi-Active Flapping Foil of the Wave Glider

Zou

et al. 2019

JMSE

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A numerical investigation is conducted to study the propulsive performance of the semi-active flapping foil of the wave glider, where the heaving smotion is fully prescribed, and the pitching motion is determined by the hydrodynamic force and torsion spring. A mesh for two-dimensional NACA0012 foil with the Reynolds number Re = 42000 is produced, and a dynamic mesh and sliding interface are used in the computation. The influences of reduced frequency, spring stiffness, and critical pitching amplitude on the hydrodynamic characteristics of semi-active flapping foil are systematically investigated. We find that there is a critical reduced frequency: When the reduced frequency is lower than the critical value, the propulsive performance of flapping foil can be improved exponentially, and when the reduced frequency is higher than the critical value, the semi-active flapping foil cannot provide an effective thrust. For a greater reduced frequency, there is an optimal spring stiffness value, which corresponds to the maximum value of the output power coefficient. For a lower reduced frequency, the mean value of the output power coefficient monotonically decreases as the spring stiffness increases. We also notice that the propulsive efficiency of flapping foil monotonically decreases as the spring stiffness increases. Finally, we find that the appropriate critical pitching amplitude can improve the propulsive performance of semi-active flapping foil, especially for greater heaving amplitudes.

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Section: The Influence Of the Reduced Frequencysupporting

confidence: 78%

Numerical Investigation of the Semi-Active Flapping Foil of the Wave Glider

Zou

et al. 2019

JMSE

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“…As a model, we still consider a passive elastic body where the actuation is localized at one extremity as defined by equation (4.1). Practical examples of such systems have been investigated recently experimentally [51,88,90,92,[95][96][97] and numerically [66,86,89,98]. Equation (4.1) can be written in the weak amplitude approximation, except for the dissipation term, which holds due to the high transversal velocities involved along the body.…”

Section: Propagating Fish-like Kinematics Of a Passive Slender Elastimentioning

confidence: 99%

On the diverse roles of fluid dynamic drag in animal swimming and flying

Godoy-Diana¹,

Thiria²

2018

J. R. Soc. Interface.

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Questions of energy dissipation or friction appear immediately when addressing the problem of a body moving in a fluid. For the most simple problems, involving a constant steady propulsive force on the body, a straightforward relation can be established balancing this driving force with a skin friction or form drag, depending on the Reynolds number and body geometry. This elementary relation closes the full dynamical problem and sets, for instance, average cruising velocity or energy cost. In the case of finite-sized and time-deformable bodies though, such as flapping flyers or undulatory swimmers, the comprehension of driving/dissipation interactions is not straightforward. The intrinsic unsteadiness of the flapping and deforming animal bodies complicates the usual application of classical fluid dynamic forces balance. One of the complications is because the shape of the body is indeed changing in time, accelerating and decelerating perpetually, but also because the role of drag (more specifically the role of the local drag) has two different facets, contributing at the same time to global dissipation and to driving forces. This causes situations where a strong drag is not necessarily equivalent to inefficient systems. A lot of living systems are precisely using strong sources of drag to optimize their performance. In addition to revisiting classical results under the light of recent research on these questions, we discuss in this review the crucial role of drag from another point of view that concerns the fluid-structure interaction problem of animal locomotion. We consider, in particular, the dynamic subtleties brought by the quadratic drag that resists transverse motions of a flexible body or appendage performing complex kinematics, such as the phase dynamics of a flexible flapping wing, the propagative nature of the bending wave in undulatory swimmers, or the surprising relevance of drag-based resistive thrust in inertial swimmers.

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“…6,7 Concentrating on the theoretical aspects of fish propulsion, Lighthill established the slender-body theory for deformable bodies to make thrust calculations. 8,9 The effect of appendage flexibility has since been investigated in pitching movements, 10,11 heaving motions, [12][13][14][15][16] and a mix of them both 17,18 or by confining the swimmer in the vicinity of a wall. 19 For all the studies mentioned, the thrust is notably enhanced when the foils are forced near their resonant frequencies.…”

Section: Introductionmentioning

confidence: 99%

Study of the thrust–drag balance with a swimming robotic fish

et al. 2018

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A robotic fish is used to test the validity of a simplification made in the context of fish locomotion. With this artificial aquatic swimmer, we verify that the momentum equation results from a simple balance between a thrust and a drag that can be treated independently in the small amplitude regime. The thrust produced by the flexible robot is proportional to A 2 f 2 , where A and f are the respective tailbeat amplitude and oscillation frequency, irrespective of whether or not f coincides with the resonant frequency of the fish. The drag is proportional to U 2 0 , where U 0 is the swimming velocity. These three physical quantities set the value of the Strouhal number in this regime. For larger amplitudes, we found that the drag coefficient is not constant but increases quadratically with the fin amplitude. As a consequence, the achieved locomotion velocity decreases, or the Strouhal number increases, as a function of the fin amplitude.

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Effect of the stiffness, inertia and oscillation kinematics on the thrust generation and efficiency of an oscillating-foil propulsion system

Cited by 16 publications

References 21 publications

Numerical Investigation of the Semi-Active Flapping Foil of the Wave Glider

Numerical Investigation of the Semi-Active Flapping Foil of the Wave Glider

On the diverse roles of fluid dynamic drag in animal swimming and flying

Study of the thrust–drag balance with a swimming robotic fish

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