Passive separation control of shortfin mako shark skin in a turbulent boundary layer

Santos, Leonardo; Lang, Amy; Wahidi, Redha; Bonacci, Andrew; Gautam, Sashank; Devey, Sean; Parsons, Jacob

doi:10.1016/j.expthermflusci.2021.110433

Cited by 10 publications

(16 citation statements)

References 52 publications

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“…The bristling is hypothesized to reduce pressure drag by inhibiting backflow in the boundary layer 143 . For an accelerating foil, a denticle-like texture was found to have delayed boundary layer separation compared to a foil with no texture 144,145 (Fig. 4d) 141,146 .…”

Section: Aquatic Bio-inspired Flow Controlmentioning

confidence: 95%

Aerial and aquatic biological and bioinspired flow control strategies

et al. 2023

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Flow control is the attempt to favorably modify a flow field’s characteristics compared to how the flow would have developed naturally along the surface. Natural flyers and swimmers exploit flow control to maintain maneuverability and efficiency under different flight and environmental conditions. Here, we review flow control strategies in birds, insects, and aquatic animals, as well as the engineered systems inspired by them. We focus mainly on passive and local flow control devices which have utility for application in small uncrewed aerial and aquatic vehicles (sUAVs) with benefits such as simplicity and reduced power consumption. We also identify research gaps related to the physics of the biological flow control and opportunities for device development and implementation on engineered vehicles.

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Section: Aquatic Bio-inspired Flow Controlmentioning

confidence: 95%

Aerial and aquatic biological and bioinspired flow control strategies

et al. 2023

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“…2016; Santos et al. 2021) have identified the bristling of shark skin and conjectured that the increased mixing helps to keep flow attached in the flank region. This work is significant in understanding the hydrodynamic effect of surface textures on the flow and forces around a swimmer; it is the first study to look at surface textures on undulating surfaces with realistic and well-defined kinematics.…”

Section: Discussionmentioning

confidence: 99%

“…2016; Santos et al. 2021). In this vein, Oeffner & Lauder (2012) tested samples of skin from the midsection of a short-fin mako shark on both a rigid flapping plate and a flexible plate.…”

Section: Introductionmentioning

confidence: 99%

A systematic investigation into the effect of roughness on self-propelled swimming plates

Massey,

Ganapathisubramani,

Weymouth

2023

J. Fluid Mech.

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This study examines the effects of surface topography on the flow and performance of a self-propelled swimming (SPS) body. We consider a thin flat plate with an egg-carton roughness texture undergoing prescribed undulatory swimming kinematics at Strouhal number $0.3$ and tail amplitude to length ratio $0.1$ ; we use plate Reynolds numbers $Re=6$ , 12 and $24\times 10^3$ , and focus on $12\,000$ . As the roughness wavelength is decreased, we find that the undulation wave speed must be increased to overcome the additional drag from the roughness and maintain SPS. Correspondingly, the extra wave speed raises the power required to maintain SPS, making the swimmer less efficient. To decouple the roughness and the kinematics, we compare the rough plates to equivalent smooth cases by matching the kinematic conditions. We find that all but the longest roughness wavelengths reduce the required swimming power and the unsteady amplitude of the forces when compared to a smooth plate undergoing identical kinematics. Additionally, roughness can enhance flow enstrophy by up to 116 % compared to the smooth cases without a corresponding spike in forces; this suggests that the increased mixing is not due to increased vorticity production at the wall. Instead, the enstrophy is found to peak strongly when the roughness wavelength is approximately twice the boundary layer thickness over the $Re$ range, indicating the roughness induces large-scale secondary flow structures that extend to the edge of the boundary layer. This study reveals the nonlinear interaction between roughness and kinematics beyond a simple increase or decrease in drag, illustrating that roughness studies on static shapes do not transfer directly to unsteady swimmers.

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“…Research has consistently shown that the passive bristling of movable scales on the shortfin mako shark (Isurus oxyrinchus) effectively controls flow separation [1][2][3][4][5][6][7][8][9][10]. Flow separation typically occurs when the reversing flow overcomes the oncoming low-momentum flow near a surface.…”

Section: Introductionmentioning

confidence: 99%

Understanding Low-Speed Streaks and Their Function and Control through Movable Shark Scales Acting as a Passive Separation Control Mechanism

Santos,

Lang,

Wahidi

et al. 2024

Biomimetics

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The passive bristling mechanism of the scales on the shortfin mako shark (Isurus oxyrinchus) is hypothesized to play a crucial role in controlling flow separation. In the hypothesized mechanism, the scales are triggered in response to patches of reversed flow at the onset of separation occurring in the low-speed streaks that form in a turbulent boundary layer. The two goals of this investigation were as follows: (1) to measure the reversing flow occurring within the low-speed streaks in a separating turbulent boundary layer; (2) to understand the passive flow control mechanism of movable shark skin scales that inhibit reversing flow within the low-speed streaks. Experiments were conducted using digital particle image velocimetry (DPIV). DPIV was used to analyze the flow in a turbulent boundary layer subjected to an adverse pressure gradient formation over both a smooth flat plate and a flat plate on which shark skin specimens were affixed. The experimental analysis of the flow over the smooth flat plate corroborated the findings of previous direct numerical simulation studies, which indicated that the average spanwise spacing of the low-speed streaks increases in the presence of adverse pressure gradients upstream of the point of separation. However, the characteristics of the flow over the shark skin specimen more closely resemble that of a zero-pressure gradient turbulent boundary layer. A comparative analysis of the width and velocity of the reversed streaks between flat plate and shark skin cases reveals that the mean spanwise spacing decreases, and thus, the number of streaks increases over the shark skin. Additionally, the reversed streaks observed over shark scales are thinner and the highest negative velocity within the streaks falls within the range required to bristle the scales.

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Passive separation control of shortfin mako shark skin in a turbulent boundary layer

Cited by 10 publications

References 52 publications

Aerial and aquatic biological and bioinspired flow control strategies

Aerial and aquatic biological and bioinspired flow control strategies

A systematic investigation into the effect of roughness on self-propelled swimming plates

Understanding Low-Speed Streaks and Their Function and Control through Movable Shark Scales Acting as a Passive Separation Control Mechanism

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