Collective locomotion of two-dimensional lattices of flapping plates. Part 2. Lattice flows and propulsive efficiency

Alben, Silas

doi:10.1017/jfm.2021.43

Cited by 9 publications

(5 citation statements)

References 28 publications

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“…Notable advancements have been made in comprehending oscillation-based principles and mechanisms. These advancements encompass a broad range of areas, including the optimisation of kinematics (Tuncer & Kaya 2005), exploration of three-dimensional effects (Dong, Mittal & Najjar 2006), manipulation of flow structures (Fish & Lauder 2006), investigation of flexibility influence (Zhu 2007; Alben 2008) as well as the study of multiple-foil configurations and collective arrangements (Muscutt, Weymouth & Ganapathisubramani 2017; Alben 2021). However, the existing studies on both the biological thrust generation and oscillating foil propulsion have been limited exclusively to homogeneous flows.…”

Section: Introductionmentioning

confidence: 99%

High propulsive performance by an oscillating foil in a stratified fluid

Wang,

Kandel,

Deng

2024

J. Fluid Mech.

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We investigate numerically the propulsion characteristics of an oscillating foil undergoing coupled heave and pitch motion in a linearly density-stratified flow. A parameter space defined by the internal Froude number ( $1 \le Fr \le 10$ ) and the maximum angle of attack ( $5^\circ \le {\alpha _0} \le 30^\circ$ ) is considered in our study. The results demonstrate a significant enhancement in both thrust production and propulsive efficiency due to the stratification influence. Notably, the highest efficiency exceeding $80\,\%$ is achieved under moderate stratification conditions, surpassing the performance observed in a homogeneous fluid. We attribute this optimum performance to the proper match between the stratification effect and foil kinematics, which gives rise to intense vortex interactions and sufficient wave–mean flow interactions in the near wake of the oscillating foil. Consequently, the energy is transferred towards wake structures to form a high-intensity momentum jet in close proximity to the foil's trailing edge, indicating efficient propulsion. Furthermore, we find that the stratifications within the moderate-to-strong transitional regime display a reduced dependence of propulsive efficiency on the maximum angle of attack, primarily due to the delaying and alleviating effects on dynamic-stall events. Such a mechanism enables the oscillating foil to maintain a satisfactory performance by sufficiently high angles of attack without the penalty of stall events. Based on our findings, we propose that animals or artificial vehicles utilising oscillatory propulsion can benefit from the presence of density stratification in the surrounding fluid.

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Section: Introductionmentioning

confidence: 99%

High propulsive performance by an oscillating foil in a stratified fluid

Wang,

Kandel,

Deng

2024

J. Fluid Mech.

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“…Here, we use “mock flocks” or groups of self-propelling foils to investigate the structural and dynamical consequences of interactions through visco-inertial flows. We focus on linear formations in which many bodies are arranged serially or in tandem and whose dynamics within the formation are free and interactive 23 , 28 , 31 , 34 , 36 , 39 . Among all configurations, this setting is perhaps the most amenable to a detailed treatment of the flow-structure interactions, since the formation and dynamical freedom are one-dimensional (1D) and the flows quasi-2D.…”

Section: Introductionmentioning

confidence: 99%

Flow interactions lead to self-organized flight formations disrupted by self-amplifying waves

Newbolt,

Lewis,

Bleu

et al. 2024

Nat Commun

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Collectively locomoting animals are often viewed as analogous to states of matter in that group-level phenomena emerge from individual-level interactions. Applying this framework to fish schools and bird flocks must account for visco-inertial flows as mediators of the physical interactions. Motivated by linear flight formations, here we show that pairwise flow interactions tend to promote crystalline or lattice-like arrangements, but such order is disrupted by unstably growing positional waves. Using robotic experiments on “mock flocks” of flapping wings in forward flight, we find that followers tend to lock into position behind a leader, but larger groups display flow-induced oscillatory modes – “flonons” – that grow in amplitude down the group and cause collisions. Force measurements and applied perturbations inform a wake interaction model that explains the self-ordering as mediated by spring-like forces and the self-amplification of disturbances as a resonance cascade. We further show that larger groups may be stabilized by introducing variability among individuals, which induces positional disorder while suppressing flonon amplification. These results derive from generic features including locomotor-flow phasing and nonreciprocal interactions with memory, and hence these phenomena may arise more generally in macroscale, flow-mediated collectives.

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“…Studies on flapping foils in side‐by‐side arrangements have demonstrated that the hydrodynamic thrust is relatively large when the foils flap in antiphase [12, 24]. Methods that solve the Navier–Stokes equations directly, such as the immersed boundary method [22, 33, 40] or marker‐and‐cell scheme [7, 8], require a fine computational grid near the bodies in order to resolve thin boundary layers and are thus limited to moderate Reynolds numbers,

{\textrm {Re}}=O(10^2)-O(10^3)

. Accurate and tractable simulations in regimes relevant to many swimming animals and biomimetic vehicles (e.g.,

{\textrm {Re}}=O(10^6)-O(10^7)

for dolphins [58]) have thus remained elusive.…”

Section: Introductionmentioning

confidence: 99%

Generalization of waving‐plate theory to multiple interacting swimmers

Baddoo

Moore

Oza

et al. 2023

Comm Pure Appl Math

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Early research in aerodynamics and biological propulsion was dramatically advanced by the analytical solutions of Theodorsen, von Kármán, Wu and others. While these classical solutions apply only to isolated swimmers, the flow interactions between multiple swimmers are relevant to many practical applications, including the schooling and flocking of animal collectives. In this work, we derive a class of solutions that describe the hydrodynamic interactions between an arbitrary number of swimmers in a two‐dimensional inviscid fluid. Our approach is rooted in multiply‐connected complex analysis and exploits several recent results. Specifically, the transcendental (Schottky–Klein) prime function serves as the basic building block to construct the appropriate conformal maps and leading‐edge‐suction functions, which allows us to solve the modified Schwarz problem that arises. As such, our solutions generalize classical thin aerofoil theory, specifically Wu's waving‐plate analysis, to the case of multiple swimmers. For the case of a pair of interacting swimmers, we develop an efficient numerical implementation that allows rapid computations of the forces on each swimmer. We investigate flow‐mediated equilibria and find excellent agreement between our new solutions and previously reported experimental results. Our solutions recover and unify disparate results in the literature, thereby opening the door for future studies into the interactions between multiple swimmers.

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Collective locomotion of two-dimensional lattices of flapping plates. Part 2. Lattice flows and propulsive efficiency

Abstract: Abstract

Cited by 9 publications

References 28 publications

High propulsive performance by an oscillating foil in a stratified fluid

High propulsive performance by an oscillating foil in a stratified fluid

Flow interactions lead to self-organized flight formations disrupted by self-amplifying waves

Generalization of waving‐plate theory to multiple interacting swimmers

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