Movable shark scales act as a passive dynamic micro-roughness to control flow separation

Lang, Amy; Bradshaw, Michael; Smith, J.; Wheelus, Jennifer; Motta, Philip; Habegger, María Laura; Hueter, Robert E.

doi:10.1088/1748-3182/9/3/036017

Cited by 51 publications

(42 citation statements)

References 28 publications

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“…Also unknown is the extent to which denticles move on their bases during locomotion and change angle relative to the skin. Motta et al () have suggested that, for shortfin mako sharks, denticles can be erected passively and that this may be used to control boundary layer profiles by inhibiting backflow (Lang et al, ). Wen et al () presented experimental data supporting an alternative hypothesis that having slightly mobile denticles would reduce the cost of locomotion by minimizing the skin bending force that results from denticle crowns pressing on each other as the body oscillates and produces skin curvature.…”

Section: Discussionmentioning

confidence: 99%

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Ankhelyi

Wainwright

Lauder

2018

Journal of Morphology

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Shark skin is covered with numerous placoid scales or dermal denticles. While previous research has used scanning electron microscopy and histology to demonstrate that denticles vary both around the body of a shark and among species, no previous study has quantified three-dimensional (3D) denticle structure and surface roughness to provide a quantitative analysis of skin surface texture. We quantified differences in denticle shape and size on the skin of three individual smooth dogfish sharks (Mustelus canis) using micro-CT scanning, gel-based surface profilometry, and histology. On each smooth dogfish, we imaged between 8 and 20 distinct areas on the body and fins, and obtained further comparative skin surface data from leopard, Atlantic sharpnose, shortfin mako, spiny dogfish, gulper, angel, and white sharks. We generated 3D images of individual denticles and measured denticle volume, surface area, and crown angle from the micro-CT scans. Surface profilometry was used to quantify metrology variables such as roughness, skew, kurtosis, and the height and spacing of surface features. These measurements confirmed that denticles on different body areas of smooth dogfish varied widely in size, shape, and spacing. Denticles near the snout are smooth, paver-like, and large relative to denticles on the body. Body denticles on smooth dogfish generally have between one and three distinct ridges, a diamond-like surface shape, and a dorsoventral gradient in spacing and roughness. Ridges were spaced on average 56 µm apart, and had a mean height of 6.5 µm, comparable to denticles from shortfin mako sharks, and with narrower spacing and lower heights than other species measured. We observed considerable variation in denticle structure among regions on the pectoral, dorsal, and caudal fins, including a leading-to-trailing edge gradient in roughness for each region. Surface roughness in smooth dogfish varied around the body from 3 to 42 microns.

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Section: Discussionmentioning

confidence: 99%

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Ankhelyi

Wainwright

Lauder

2018

Journal of Morphology

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“…In recent years, considerable progress has been made in the design and manufacture of nanomaterials, nanodevices, functional surfaces, etc. by mimicking biology and nature ( Bhushan, 2009 ; Dean and Bhushan, 2012 ; Lang et al, 2014 ). A fine example of bionic design is the biomimetic drag reduction that is achieved using a special microstructure surface which emulates the non-smooth surface of certain natural organisms.…”

Section: Introductionmentioning

confidence: 99%

Preparation, anti-biofouling and drag-reduction properties of a biomimetic shark skin surface

Hanlu

2016

Biology Open

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Shark skin surfaces show non-smoothness characteristics due to the presence of a riblet structure. In this study, biomimetic shark skin was prepared by using the polydimethylsiloxane (PDMS)-embedded elastomeric stamping (PEES) method. Scanning electron microscopy (SEM) was used to examine the surface microstructure and fine structure of shark skin and biomimetic shark skin. To analyse the hydrophobic mechanism of the shark skin surface microstructure, the effect of biomimetic shark skin surface microstructure on surface wettability was evaluated by recording water contact angle. Additionally, protein adhesion experiments and anti-algae adhesion performance testing experiments were used to investigate and evaluate the anti-biofouling properties of the surface microstructure of biomimetic shark skin. The recorded values of the water contact angle of differently microstructured surfaces revealed that specific microstructures have certain effects on surface wettability. The anti-biofouling properties of the biomimetic shark skin surface with microstructures were superior to a smooth surface using the same polymers as substrates. Moreover, the air layer fixed on the surface of the biomimetic shark skin was found to play a key role in their antibiont adhesion property. An experiment into drag reduction was also conducted. Based on the experimental results, the microstructured surface of the prepared biomimetic shark skin played a significant role in reducing drag. The maximum of drag reduction rate is 12.5%, which is higher than the corresponding maximum drag reduction rate of membrane material with a smooth surface.

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“…Past studies have demonstrated that shark scales are flexibly connected to the underlying skin and thus are capable of bristling [8] and that preventing scales from bristling increases backflow in a turbulent, reversing flow [43,44], but this study provides the first direct documentation of passive bristling by shark scales in reversing flows. If scale bristling functions in drag reduction of these high Re swimmers, there would be strong selective pressure for this mechanism to function at cruising speeds.…”

Section: Discussionmentioning

confidence: 72%

Passive bristling of mako shark scales in reversing flows

Clos

Lang

Devey

et al. 2018

J. R. Soc. Interface.

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Shark skin has been shown to reduce drag in turbulent boundary layer flows, but the flow control mechanisms by which it does so are not well understood. Drag reduction has generally been attributed to static effects of scale surface morphology, but possible drag reduction effects of passive or active scale actuation, or 'bristling', have been recognized more recently.Here, we provide the first direct documentation of passive scale bristling due to reversing, turbulent boundary layer flows. We recorded and analysed high-speed videos of flow over the skin of a shortfin mako shark, Isurus oxyrinchus. These videos revealed rapid scale bristling events with mean durations of approximately 2 ms. Passive bristling occurred under flow conditions representative of cruise swimming speeds and was associated with two flow features. The first was a downward backflow that pushed a scale-up from below. The second was a vortex just upstream of the scale that created a negative pressure region, which pulled up a scale without requiring backflow. Both flow conditions initiated bristling at lower velocities than those required for a straight backflow. These results provide further support for the role of shark scale bristling in drag reduction.rsif.royalsocietypublishing.org J. R. Soc. Interface 15: 20180473

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Movable shark scales act as a passive dynamic micro-roughness to control flow separation

Cited by 51 publications

References 28 publications

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Preparation, anti-biofouling and drag-reduction properties of a biomimetic shark skin surface

Passive bristling of mako shark scales in reversing flows

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