Microswimmers in an axisymmetric vortex flow

Arguedas-Leiva, José-Agustín; Wilczek, Michael

doi:10.1088/1367-2630/ab776f

Cited by 19 publications

(13 citation statements)

References 47 publications

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“…1, where we show (a,c) the probability density function (PDF) of swimmer vertical position, P (z), and (b,d) the conditional average n x cos z|z for Λ = 0.98. We show the results both for the original deterministic dynamics (12)(13) and in the presence of rotational noise that is added to Eq. ( 13) in the form of a stochastic term, 2Pe −1 r η(t), where Pe r = U 0 /(LD r ) denotes the rotational Péclet number, defined in terms of the rotational diffusion coefficient, D r .…”

Section: Steady Laminar Kolmogorov Flowmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…[6] it has been clarified that depending on noise, swimming velocity and aspect ratio, swimmers may accumulate in regions of either high or low shear rate in the laminar Kolmogorov flow. In general, it is now well recognized that the interplay between swimming, flow and noise produces a variety of effects in laminar, chaotic and turbulent flows, including preferential accumulation of swimmers [7][8][9][10][11][12][13], clustering [14,15], enhanced transport [13] and it can affect chemotaxis [7] and biofilm formation [16].Besides accumulation, swimming microorganisms have been observed to align with local flow properties. For instance, even in presence of strong turbulent fluctuations, elongated swimmers, such as bacteria, are found to align nematically with vorticity [14,15].…”

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confidence: 99%

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Alignment of elongated swimmers in a laminar and turbulent Kolmogorov flow

Borgnino,

Boffetta,

Cencini

et al. 2022

Preprint

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Many aquatic microorganisms are able to swim. In natural environments they typically do so in the presence of flows. In recent years it has been shown that the interplay of swimming and flows can give rise to interesting and biologically relevant phenomena, such as accumulation of microorganisms in specific flow regions and local alignment with the flow properties. Here, we consider a mechanical model for elongated microswimmers in a Kolmogorov flow, a prototypic shear flow, both in steady and in turbulent conditions. By means of direct numerical simulations, supported by analytical calculation in a simplified stochastic setting, we find that the alignment of the swimming direction with the local velocity is a general phenomenon. We also explore how the accumulation of microorganisms, typically observed in steady flows, is modified by the presence of unsteady fluctuations. I. INTRODUCTIONMany microorganisms, from bacteria to microalgae, are motile and capable of swimming [1]. From biological fluids to lakes and oceans, swimming microorganisms have to adapt their motility to the surrounding fluid conditions in order to find food, escape from predators, optimize light uptake and mate [2]. Complex biological mechanisms are often involved in controlling the swimming direction of microorganisms, by producing directed motility cued on chemical or physical signals (such as chemo/photo/rheo taxis) [1]. The study of simple mechanistic models has shown that the interplay of swimming and flow is relevant in determining the dynamics of such organisms. The analysis of deterministic models for ellipsoidal swimmers shows that, in a two-dimensional, laminar Poiseuille flow the equations of motion for the swimmer are formally akin to those of a pendulum. For a wide range of parameters, the dynamics can be divided into two families of trajectories [3,4]. Trajectories close to the channel center encounter small velocity gradients and are characterized by an oscillating swimming direction, analogous to pendulum oscillations, while trajectories in the high-shear regions, close to the walls, show tumbling motion, the equivalent of librations. Recent experimental works have confirmed these findings in a strain of smooth-swimming E. Coli in a Poiseuille flow [5]. Other parallel flows (such as the Kolmogorov flow) show similar behaviours [6]. Such swimming dynamics can cause accumulation (trapping) of elongated microswimmers in high shear regions [7] (see also [8]). Preferential trapping in high-shear regions has been observed also for gyrotactic algae, although induced by a different mechanism, i.e. the competition by flow-induced rotation and upwards-biased swimming. [9,10]. The dynamics is in general modified by the presence of noise [5,6,11] or steric interactions with the walls [3], which however do not necessarily disrupt its effects. In particular, in Ref. [6] it has been clarified that depending on noise, swimming velocity and aspect ratio, swimmers may accumulate in regions of either high or low shear rate in the laminar Kolmogo...

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Section: Steady Laminar Kolmogorov Flowmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Alignment of elongated swimmers in a laminar and turbulent Kolmogorov flow

Borgnino,

Boffetta,

Cencini

et al. 2022

Preprint

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“…a donut. Remarkably, the system (3) is conservative, as is the dynamics of ellipsoidal swimmers in 2D and 3D Poiseuille flows [11,12], spherical gyrotactic swimmers in Kolmogorov flows [13], and spherical swimmers in 2D vortex flows [16]. The conserved quantity may be derived in the standard way.…”

Section: Flowmentioning

confidence: 99%

Noise-induced aggregation of swimmers in the Kolmogorov flow

Berman,

Ferguson,

Bizzak

et al. 2021

Preprint

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We investigate a model for the dynamics of ellipsoidal microswimmers in an externally imposed, laminar Kolmogorov flow. Through a phase-space analysis of the dynamics without noise, we find that swimmers favor either cross-stream or rotational drift, depending on their swimming speed and aspect ratio. When including noise, i.e. rotational diffusion, we find that swimmers are driven into certain parts of phase space, leading to a nonuniform steady-state distribution. This distribution exhibits a transition from swimmer aggregation in low-shear regions of the flow to aggregation in high-shear regions as the swimmer's speed, aspect ratio, and rotational diffusivity are varied. To explain the nonuniform phase-space distribution of swimmers, we apply a weaknoise averaging principle that produces a reduced description of the stochastic swimmer dynamics.Using this technique, we find that certain swimmer trajectories are more favorable than others in the presence of weak rotational diffusion. By combining this information with the phase-space speed of swimmers along each trajectory, we predict the regions of phase space where swimmers tend to accumulate. The results of the averaging technique are in good agreement with direct calculations of the steady-state distributions of swimmers. In particular, our analysis explains the transition from low-shear to high-shear aggregation.

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“…In our model, an ellipsoidal swimmer in two dimensions (2D) is described by q = (r, n), comprising its position r = (x, y) and swimming direction n = (cos θ, sin θ). Absent noise and active torques, a swimmer with a fixed swimming speed v 0 in a fluid velocity field u(r) obeys [14,15,29,30]…”

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confidence: 99%

Transport barriers to self-propelled particles in fluid flows

Berman,

Buggeln,

Brantley

et al. 2020

Preprint

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We present theory and experiments demonstrating the existence of invariant manifolds that impede the motion of microswimmers in two-dimensional fluid flows. One-way barriers are apparent in a hyperbolic fluid flow that block the swimming of both smooth-swimming and run-and-tumble Bacillus subtilis bacteria. We identify key phase-space structures, called swimming invariant manifolds (SwIMs), that serve as separatrices between different regions of long-time swimmer behavior. When projected into xy-space, the edges of the SwIMs act as one-way barriers, consistent with the experiments.

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Microswimmers in an axisymmetric vortex flow

Cited by 19 publications

References 47 publications

Alignment of elongated swimmers in a laminar and turbulent Kolmogorov flow

Alignment of elongated swimmers in a laminar and turbulent Kolmogorov flow

Noise-induced aggregation of swimmers in the Kolmogorov flow

Transport barriers to self-propelled particles in fluid flows

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