Specialization of tuna: A numerical study on the function of caudal keels

Zhang, Jun-Duo; Sung, Hyung Jin; Huang, Wei‐Xi

doi:10.1063/5.0029340

Cited by 26 publications

(17 citation statements)

References 68 publications

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“…2017) and numerical studies (Wang et al. 2020; Yao & Yeo 2020; Zhang, Sung & Huang 2020) have been performed. Major mechanisms employed by animals to improve their performance include the added-mass effect (Sane 2003), leading-edge vortex (LEV) effect (Birch & Dickinson 2001; Garmann, Visbal & Orkwis 2013; Bottom et al.…”

Section: Introductionmentioning

confidence: 99%

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Vortex dynamics and hydrodynamic performance enhancement mechanism in batoid fish oscillatory swimming

et al. 2021

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The effects of chordwise deformation and the half-amplitude asymmetry on the hydrodynamic performance and vortex dynamics of batoid fish have been numerically investigated, in which the two parameters were represented by the wavenumber ( $W$ ) and the ratio of the half-amplitude above the longitudinal axis to that below ( $HAR$ ). Fin kinematics were prescribed based on biological data. Simulations were conducted using the immersed boundary method. It was found that moderate chordwise deformation enhances the thrust, saves the power and increases the efficiency. A large $HAR$ can also increase thrust performance. By using the derivative-moment transformation theory at several subdomains to capture the local vortical structures and a force decomposition, it was shown that, at high Strouhal numbers ( $St$ ), the tip vortex is the main source of thrust, whereas the leading-edge vortex (LEV) and trailing-edge vortex weaken the thrust generation. However, at lower $St$ , the LEV would enhance the thrust. The least deformation ( $W=0$ ) leads to the largest effective angle of attack, and thus the strongest vortices. However, moderate deformation ( $W=0.4$ ) has an optimal balance between the performance enhancement and the opposite effect of different local structures. The performance enhancement of $HAR$ was also due to the increase of the vortical contributions. This work provides a new insight into the role of vortices and the force enhancement mechanism in aquatic swimming.

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Section: Introductionmentioning

confidence: 99%

“…Zhang et al. (2020) carried out a study on the function of caudal keels for tuna swimming, in which thrust enhancement was also observed. The reason is that the caudal keels generate LEVs causing negative pressure, and the enhancement becomes more significant as the Strouhal number and Reynolds number increase.…”

Section: Introductionmentioning

confidence: 99%

Vortex dynamics and hydrodynamic performance enhancement mechanism in batoid fish oscillatory swimming

et al. 2021

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“…2017), pitching airfoils (Senturk & Smits 2019) and tunas (Zhang et al. 2020). However, Borazjani & Sotiropoulos (2010) observed that anguilliform swimmers, i.e.…”

Section: Discussionmentioning

confidence: 99%

Hydrodynamics of a swimming batoid fish at Reynolds numbers up to 148 000

Dong

Huang

2023

J. Fluid Mech.

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Flow around a tethered model of a swimming batoid fish is studied by using the wall-modelled large-eddy simulation in conjunction with the immersed boundary method. A Reynolds number ( $Re$ ) up to 148 000 is chosen, and it is comparable to that of a medium-sized aquatic animal in cruising swimming state. At such a high $Re$ , we provide, to the best of our knowledge, the first evidence of hairpin vortical (HV) structures near the body surface using three-dimensional high-fidelity flow field data. It is observed that such small-scale vortical structures are mainly formed through two mechanisms: the leading-edge vortex (LEV)–secondary filament–HV and LEV–HV transformations in different regions. The HVs create strong fluctuations in the pressure distribution and frequency spectrum. Simulations are also conducted at $Re=1480$ and 14 800 to reveal the effect of Reynolds number. Variations of the flow separation behaviour and local pressure with $Re$ are presented. Our results indicate that low- $Re$ simulations are meaningful when the focus is on the force variation tendency, whereas high- $Re$ simulations are needed when concerning flow fluctuations and turbulence mechanisms.

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“…2016; Zhang et al . 2020). Therefore, given their structural affinities, it is reasonable to presume that the pre‐caudal scaly keel in Saurostomus had similar hydrodynamic functions.…”

Section: Discussionmentioning

confidence: 99%

Revision of the pachycormid fish Saurostomus esocinus Agassiz from the Early Jurassic (Toarcian) of Europe, with new insight into the origins of suspension‐feeding in Pachycormidae

Cooper

Maxwell

2022

Papers in Palaeontology

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The Early Jurassic Posidonienschiefer Formation in south‐west Germany (Toarcian) records the first appearance of the stem‐teleost group Pachycormidae in the fossil record. However, most pachycormid taxa remain poorly diagnosed or undescribed, making questions of the morphological underpinnings of trophic diversification in the group difficult to address. Here we re‐describe Saurostomus esocinus, a large (≤1710 mm) pelagic pachycormid, based on material from the type formation. Additional material of Saurostomus is identified in near‐coeval strata in Luxembourg, France and the UK, demonstrating a broad European distribution. We assign a neotype, and provide the first formal diagnosis and cranial reconstruction for this genus. Historical misconceptions regarding taxonomic identity of Saurostomus have caused numerous specimens to be conflated with the better known genus Pachycormus. In south‐west Germany, Saurostomus is stratigraphically distributed across the tenuicostatum and serpentinum Zones, encapsulating six ammonite subzones, with an individual from the paltum subzone representing the oldest stratigraphic occurrence of Pachycormidae. Stout recurved teeth, powerful pectoral fins, a streamlined body, a pre‐caudal scaly keel and remnants of coleoid gut contents indicate fast swimming capabilities and a pelagic teuthophagous ecology for Saurostomus esocinus. Cladistic analysis retains Saurostomus as sister to a clade comprising Ohmdenia and the suspension‐feeding pachycormids. Several character states associated with the evolution of suspension‐feeding are shared with Saurostomus, indicating S. esocinus, rather than Ohmdenia, to be the most basal pachycormid to have transitional suspension‐feeding characteristics. The divergence of the suspension‐feeding and macrophagous pachycormids therefore pre‐dates the paltum subzone of the lower Toarcian.

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Specialization of tuna: A numerical study on the function of caudal keels

Cited by 26 publications

References 68 publications

Vortex dynamics and hydrodynamic performance enhancement mechanism in batoid fish oscillatory swimming

Vortex dynamics and hydrodynamic performance enhancement mechanism in batoid fish oscillatory swimming

Hydrodynamics of a swimming batoid fish at Reynolds numbers up to 148 000

Revision of the pachycormid fish Saurostomus esocinus Agassiz from the Early Jurassic (Toarcian) of Europe, with new insight into the origins of suspension‐feeding in Pachycormidae

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