The fish tail motion forms an attached leading edge vortex

Borazjani, Iman; Daghooghi, Mohsen

doi:10.1098/rspb.2012.2071

Cited by 128 publications

(109 citation statements)

References 39 publications

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“…Most sharks do not swim at high speed for the majority of their daily activity pattern, and common cruising speeds for many sharks, including those species classically considered to be high-speed specialists, fall in the range of 0.5-1.0 body lengths s . Under these conditions, our data show that flow over the body and fins is likely to be complex, with separation bubbles and LEVs forming (Borazjani and Daghooghi, 2013). This greatly complicates our current view of laminar flows over the body and fins of swimming sharks as commonly depicted in the literature.…”

Section: D Printed Shark Skin Under Dynamic Conditionsmentioning

confidence: 40%

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Biomimetic shark skin: design, fabrication and hydrodynamic function

Wen

Weaver

Lauder

2014

Journal of Experimental Biology

384

284

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Although the functional properties of shark skin have been of considerable interest to both biologists and engineers because of the complex hydrodynamic effects of surface roughness, no study to date has successfully fabricated a flexible biomimetic shark skin that allows detailed study of hydrodynamic function. We present the first study of the design, fabrication and hydrodynamic testing of a synthetic, flexible, shark skin membrane. A three-dimensional (3D) model of shark skin denticles was constructed using micro-CT imaging of the skin of the shortfin mako (Isurus oxyrinchus). Using 3D printing, thousands of rigid synthetic shark denticles were placed on flexible membranes in a controlled, linear-arrayed pattern. This flexible 3D printed shark skin model was then tested in water using a robotic flapping device that allowed us to either hold the models in a stationary position or move them dynamically at their self-propelled swimming speed. Compared with a smooth control model without denticles, the 3D printed shark skin showed increased swimming speed with reduced energy consumption under certain motion programs. For example, at a heave frequency of 1.5 Hz and an amplitude of ±1 cm, swimming speed increased by 6.6% and the energy cost-of-transport was reduced by 5.9%. In addition, a leadingedge vortex with greater vorticity than the smooth control was generated by the 3D printed shark skin, which may explain the increased swimming speeds. The ability to fabricate synthetic biomimetic shark skin opens up a wide array of possible manipulations of surface roughness parameters, and the ability to examine the hydrodynamic consequences of diverse skin denticle shapes present in different shark species.

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Section: D Printed Shark Skin Under Dynamic Conditionsmentioning

confidence: 40%

“…Borazjani and Daghooghi, 2013). In our study, the flapping biomimetic shark skin membrane generated a stronger LEV than that of the smooth foil (Fig.…”

Section: D Printed Shark Skin Under Dynamic Conditionsmentioning

confidence: 92%

Biomimetic shark skin: design, fabrication and hydrodynamic function

Wen

Weaver

Lauder

2014

Journal of Experimental Biology

384

284

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“…Vortical patterns in the frontal plane received most attention [5][6][7], with few studies on axial vorticity [7,8] and vorticity near the leading edge of the tail fin [9]. Computational studies predict that different vortical flows blend in the wake [8] and may interact to enhance performance in flyers [10] and swimmers [11], yet we lack studies that quantify the propulsive contributions of these flows, such as edge vortices, in undulatory swimmers.…”

Section: Introductionmentioning

confidence: 99%

Fish larvae exploit edge vortices along their dorsal and ventral fin folds to propel themselves

Müller

Leeuwen

et al. 2016

J. R. Soc. Interface.

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Larvae of bony fish swim in the intermediate Reynolds number (Re) regime, using body-and caudal-fin undulation to propel themselves. They share a median fin fold that transforms into separate median fins as they grow into juveniles. The fin fold was suggested to be an adaption for locomotion in the intermediate Reynolds regime, but its fluid-dynamic role is still enigmatic. Using three-dimensional fluid-dynamic computations, we quantified the swimming trajectory from body-shape changes during cyclic swimming of larval fish. We predicted unsteady vortices around the upper and lower edges of the fin fold, and identified similar vortices around real larvae with particle image velocimetry. We show that thrust contributions on the body peak adjacent to the upper and lower edges of the fin fold where large left-right pressure differences occur in concert with the periodical generation and shedding of edge vortices. The fin fold enhances effective flow separation and drag-based thrust. Along the body, net thrust is generated in multiple zones posterior to the centre of mass. Counterfactual simulations exploring the effect of having a fin fold across a range of Reynolds numbers show that the fin fold helps larvae achieve high swimming speeds, yet requires high power. We conclude that propulsion in larval fish partly relies on unsteady high-intensity vortices along the upper and lower edges of the fin fold, providing a functional explanation for the omnipresence of the fin fold in bony-fish larvae.

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“…In laminar flow conditions, it has been found on autorotating seeds [7] and on the wings of insects [8] and small birds [9]. In transitional and turbulent flow conditions, it has been found on larger bird wings [10], fish fins [11] and delta wings [12,13]. In helicopter rotors [14] and wind turbines [15], the LEV is a powerful but undesirable flow feature.…”

Section: The Leading Edge Vortexmentioning

confidence: 99%

The leading-edge vortex of yacht sails

Arredondo-Galeana

Viola

2018

Ocean Engineering

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It has been suggested that a stable Leading Edge Vortex (LEV) can be formed from the sharp leading edge of asymmetric spinnakers. If the LEV remains stably attached to the leading edge, it provides an increase in the thrust force. Until now, however, the existence of a stable and attached LEV has only been shown by numerical simulations. In the present work we experimentally verify, for the first time, that a stable LEV can be formed on an asymmetric spinnaker. We tested a 3D printed rigid sail in a water flume at a chord-based Reynolds number of ca. 104 . The sail was tested in isolation (no hull and rigging) at an incidence with the flow equivalent to an apparent wind angle of 55• and a heel angle of 10 • . The flow field was measured with particle image velocimetry over horizontal cross sections. We found that on the leeward side of the sail, the flow separates at the leading edge reattaching further downstream and forming a stable LEV. The LEV grows in diameter from the root to the tip of the sail, where it merges with the tip vortex. We detected the LEV using the γ 1 and γ 2 criteria, and we verified its stability over time. The lift contribution provided by the LEV was computed solving a complex potential model of each sail section. This analysis showed that the LEV provides more than 10% of the total sail's lift. These findings suggests that the performance of asymmetric spinnakers could be significantly enhanced by promoting a stable LEV.

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The fish tail motion forms an attached leading edge vortex

Cited by 128 publications

References 39 publications

Biomimetic shark skin: design, fabrication and hydrodynamic function

Biomimetic shark skin: design, fabrication and hydrodynamic function

Fish larvae exploit edge vortices along their dorsal and ventral fin folds to propel themselves

The leading-edge vortex of yacht sails

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