On the role of added mass and vorticity release for self-propelled aquatic locomotion

Paniccia, Damiano; Graziani, G.; Lugni, Claudio; Piva, R.

doi:10.1017/jfm.2021.375

Cited by 14 publications

(8 citation statements)

References 49 publications

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“…As anticipated above, for small pitch angles, i.e. for going to one, the prediction of the asymptotic velocity equal to c is confirmed by the numerical results which also show how the locomotion speed is practically independent of the trailing edge amplitude , as for undulatory swimming in the specific case of inviscid flows 31 . For zero resistance, the Froude efficiency continuously decreases up to a null value at steady state where the net thrust is going to vanish.…”

Section: Resultssupporting

confidence: 78%

“…It follows that the total impulse , which does not suffer the poor convergence of the momentum over an unbounded domain 42 , 43 and whose time derivative gives the forces exchanged between the body and the surrounding fluid, may be expressed as the sum of the potential and vortical impulses, and , as where the bound vorticity due to , properly added to the released vorticity , gives the additional vorticity introduced by Lighthill. The mathematical model, described in detail for undulatory free swimming in Paniccia et al 31 , has been partially reported in the Supplementary Material and properly reshaped for the axial oscillatory swimming given by a flapping foil in the presence of a virtual body. The flow solutions are obtained by a simple inviscid procedure easily extendable to a classical vortex method by introducing the diffusion of the vorticity as detailed in a previous paper 44 .…”

Section: Methodsmentioning

confidence: 99%

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The performance of a flapping foil for a self-propelled fishlike body

Paniccia

Padovani

Graziani

et al. 2021

Sci Rep

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Several fish species propel by oscillating the tail, while the remaining part of the body essentially contributes to the overall drag. Since in this case thrust and drag are in a way separable, most attention was focused on the study of propulsive efficiency for flapping foils under a prescribed stream. We claim here that the swimming performance should be evaluated, as for undulating fish whose drag and thrust are severely entangled, by turning to self-propelled locomotion to find the proper speed and the cost of transport for a given fishlike body. As a major finding, the minimum value of this quantity corresponds to a locomotion speed in a range markedly different from the one associated with the optimal efficiency of the propulsor. A large value of the feathering parameter characterizes the minimum cost of transport while the optimal efficiency is related to a large effective angle of attack. We adopt here a simple two-dimensional model for both inviscid and viscous flows to proof the above statements in the case of self-propelled axial swimming. We believe that such an easy approach gives a way for a direct extension to fully free swimming and to real-life configurations.

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Section: Resultssupporting

confidence: 78%

Section: Methodsmentioning

confidence: 99%

The performance of a flapping foil for a self-propelled fishlike body

Paniccia

Padovani

Graziani

et al. 2021

Sci Rep

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show abstract

“…For the undulating swimmer, the added mass plays a dominant role in the propulsive performance (Lighthill 1970, Candelier, Boyer & Leroyer 2011, Eloy, 2012, Paniccia et al. 2021). In the elongated-body theory (Lighthill 1970), the added mass per unit length at the foil trailing edge can be calculated from a curvilinear coordinate system as ρ h 2 /4, where h denotes the thickness of the foil and is assumed to be smaller enough, i.e.…”

Section: Resultsmentioning

confidence: 99%

Hydrodynamic performance of slender swimmer: effect of travelling wavelength

2022

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The impact of Strouhal number St (= 0.1–1.0), Reynolds number Re (= 50–2000) and dimensionless wavelength λ (= 0.5–2.0) on the hydrodynamic performance of a travelling wavy foil of a constant length is extensively investigated. The relationship of time-mean thrust with St, Re and λ is presented, suggesting that the propulsive force increases with increasing St, Re and λ. As such, the drag–thrust boundary advances as these parameters increase. A shorter λ makes the thrust steadier while a longer λ enhances the maximum instantaneous thrust. The latter is beneficial for prey to escape from a predator. The fluid added mass caused by the foil oscillation increases with St and λ but declines with Re (<500). Seven types of wake structures produced by the foil are identified, discussed and connected to thrust generation, showing how St, Re and λ affect the fluid dynamics, wake transition, vortex strength, wake jet, velocity, added mass, added damping, power input, efficiency and pressure profiles. The outcome of this work renders a physical basis for understanding the swimming of aquatic animals.

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“…We may then express and , via a Helmholtz decomposition, in terms of their potential and vortical contributions as and , where the added mass effects are embedded within the potential impulses and while the vortical impulses and are related to the vortex sheet around the body and to the vortices shed into the wake 33 – 35 . A complete and detailed description of the procedure can be found in Paniccia et al 36 , where all the steps up to the final system of equations written in the body fixed frame are reported to obtain the two linear velocity components U and V and the angular velocity where the added mass coefficients , which are usually fully embedded into the forcing terms for standard CFD simulations 37 , are here easily obtained by the following definition In the above system the potential impulses have been split into some terms related to the unknown rigid body motions, which are expressed through the added mass coefficients, and other terms with the subscript sh , due to the shape deformation, which remain on the r.h.s. of the equations together with the vortical contribution.…”

Section: Methodsmentioning

confidence: 99%

The fish ability to accelerate and suddenly turn in fast maneuvers

Paniccia

Graziani

Lugni

et al. 2022

Sci Rep

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Velocity burst and quick turning are performed by fish during fast maneuvers which might be essential to their survival along pray–predator encounters. The parameters to evaluate these truly unsteady motions are totally different from the ones for cruising gaits since a very large acceleration, up to several times the gravity, and an extreme turning capability, in less than one body length, are now the primary requests. Such impressive performances, still poorly understood, are not common to other living beings and are clearly related to the interaction with the aquatic environment. Hence, we focus our attention on the water set in motion by the body, giving rise to the relevant added mass and the associated phenomena in transient conditions, which may unveil the secret of the great maneuverability observed in nature. Many previous studies were almost exclusively concentrated on the vortical wake, whose account, certainly dominant at steady state, is not sufficient to explain the entangled transient phenomena. A simple two-dimensional impulse model with concentrated vorticity is used for the self-propulsion of a deformable body in an unbounded fluid domain, to single out the potential and the vortical impulses and to highlight their interplay induced by recoil motions.

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On the role of added mass and vorticity release for self-propelled aquatic locomotion

Abstract: Abstract

Cited by 14 publications

References 49 publications

The performance of a flapping foil for a self-propelled fishlike body

The performance of a flapping foil for a self-propelled fishlike body

Hydrodynamic performance of slender swimmer: effect of travelling wavelength

The fish ability to accelerate and suddenly turn in fast maneuvers

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