Computational mean-field modeling of confined active fluids

Theillard, Maxime; Saintillan, David

doi:10.1016/j.jcp.2019.07.040

Cited by 28 publications

(35 citation statements)

References 62 publications

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“…The fundamental premise of non-interacting active Brownian particles glosses over many details that may become relevant in specific systems. For instance, future work should address the roles of hydrodynamic interactions with obstacles [10], swimmer-specific scattering dynamics [45], rheological effects due to activity [46], and the potential emergence of spontaneous flows and active turbulence in denser systems [47,48]. ACKNOWLEDGMENTS D.S.…”

Section: Discussionmentioning

confidence: 99%

“…As we showed in Eqs. (41) and (48), the asymptotic transport velocity U depends on the first global moment M 1 , while the dispersion dyadic D requires knowledge of the second global moment M 2 ; higher-order moments of the Lagrangian particle displacement would similarly involve global moments of higher orders, e.g. M 3 .…”

Section: Summary Of the Macrotransport Modelmentioning

confidence: 99%

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Transport and dispersion of active particles in periodic porous media

2019

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The transport of self-propelled particles such as bacteria and phoretic swimmers through crowded heterogeneous environments is relevant to many natural and engineering processes, from biofilm formation and contamination processes to transport in soils and biomedical devices. While there has been experimental progress, a theoretical understanding of mean transport properties in these systems has been lacking. In this work, we apply generalized Taylor dispersion theory to analyze the long-time statistics of an active self-propelled Brownian particle transported under an applied flow through the interstices of a periodic lattice that serves as an idealization of a porous medium. Our theoretical model, which we validate against Brownian dynamics simulations, is applied to unravel the roles of motility, fluid flow, and lattice geometry on asymptotic mean velocity and dispersivity. In weak flows, transport is dominated by active dispersion, which results from self-propulsion in the presence of noise and is hindered by the obstacles that act as entropic barriers. In strong flows, shear-induced Taylor dispersion becomes the dominant mechanism for spreading, with pillars now acting as regions of shear production that enhance dispersion. The interplay of these two effects leads to complex and unexpected trends, such as a non-monotonic dependence of axial dispersivity on flow strength and a reduction in dispersion due to swimming activity in strong flows. Brownian dynamics are used to cast light on the pre-asymptotic regime, where tailed distributions are observed in agreement with recent experiments on motile micro-organisms. Our results also highlight the subtle effects of pillar shape, which can be used to control the magnitude of dispersion and to drive a net particle migration in quiescent systems.

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Section: Discussionmentioning

confidence: 99%

Section: Summary Of the Macrotransport Modelmentioning

confidence: 99%

Transport and dispersion of active particles in periodic porous media

2019

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“…The z-invariance assumption significantly reduces the computational cost and is often used to solve numerically similar kinetic models [32,42,44]. Full three-dimensional (3D) simulations are performed for suspensions of elongated bacteria undergoing a purely hydrodynamic instability with [51] and without [52] confinement. It emerges that the observed 3D patterns closely resemble the ones observed in 2D simulations, suggesting that the present approach provides correct qualitative predictions of the suspension's dynamics.…”

Section: A Numerical Methodsmentioning

confidence: 99%

Hydrochemical interactions in dilute phoretic suspensions: From individual particle properties to collective organization

Traverso

Michelin

2020

Phys. Rev. Fluids

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Janus phoretic colloids (JPs) self-propel as a result of self-generated chemical gradients and exhibit spontaneous nontrivial dynamics within phoretic suspensions, on length scales much larger than the microscopic swimmer size. Such collective dynamics arise from the competition of (i) the self-propulsion velocity of the particles, (ii) the attractive/repulsive chemically mediated interactions between particles, and (iii) the flow disturbance they introduce in the surrounding medium. These three ingredients are directly determined by the shape and physicochemical properties of the colloids' surface. Owing to such link, we adapt a recent and popular kinetic model for dilute suspensions of chemically active JPs where the particle's far-field hydrodynamic and chemical signatures are intrinsically linked and explicitly determined by the design properties. Using linear stability analysis, we show that self-propulsion can induce a wave-selective mechanism for certain particles' configurations consistent with experimental observations. Numerical simulations of the complete kinetic model are further performed to analyze the relative importance of chemical and hydrodynamic interactions in the nonlinear dynamics. Our results show that regular patterns in the particle density are promoted by chemical signaling but prevented by the strong fluid flows generated collectively by the polarized particles, regardless of their chemotactic or antichemotactic nature, i.e., for both puller and pusher swimmers.

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“…At significantly higher densities, there emerges a typical length scale of the vortices, which is comparable to about 5-10 times the bacterial size [28,30,31]. Although this sequence of dynamical states has never been simultaneously observed in a single systematic bulk experiment, with the exception of Sokolov et al [26], the transition scenario is supported by computer simulations of self-propelled particles interacting through various forms of long-ranged hydrodynamic fields and short-ranged steric repulsion [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46].…”

Section: Introductionmentioning

confidence: 92%

Swimming Suppresses Correlations in Dilute Suspensions of Pusher Microorganisms

et al. 2020

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Active matter exhibits various forms of nonequilibrium states in the absence of external forcing, including macroscopic steady-state currents. Such states are often too complex to be modeled from first principles, and our understanding of their physics relies heavily on minimal models. These are mostly studied in the case of "dry" active matter, where particle dynamics are dominated by friction with their surroundings. Significantly less is known about systems with long-range hydrodynamic interactions that belong to "wet" active matter. Dilute suspensions of motile bacteria, modeled as self-propelled dipolar particles interacting solely through long-ranged hydrodynamic fields, are arguably the most studied example from this class of active systems. Their phenomenology is well established: At a sufficiently high density of bacteria, there appear large-scale vortices and jets comprising many individual organisms, forming a chaotic state commonly known as bacterial turbulence. As revealed by computer simulations, below the onset of collective motion, the suspension exhibits very strong correlations between individual microswimmers stemming from the long-ranged nature of dipolar fields. Here, we demonstrate that this phenomenology is captured by the minimal model of microswimmers. We develop a kinetic theory that goes beyond the commonly used mean-field assumption and explicitly takes into account such correlations. Notably, these can be computed exactly within our theory. We calculate the fluid velocity variance, spatial and temporal correlation functions, the fluid velocity spectrum, and the enhanced diffusivity of tracer particles. We find that correlations are suppressed by particle self-propulsion, although the mean-field behavior is not restored even in the limit of very fast swimming. Our theory is not perturbative and is valid for any value of the microswimmer density below the onset of collective motion. This work constitutes a significant methodological advance and allows us to make qualitative and quantitative predictions that can be directly compared to experiments and computer simulations of microswimmer suspensions.

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Computational mean-field modeling of confined active fluids

Cited by 28 publications

References 62 publications

Transport and dispersion of active particles in periodic porous media

Transport and dispersion of active particles in periodic porous media

Hydrochemical interactions in dilute phoretic suspensions: From individual particle properties to collective organization

Swimming Suppresses Correlations in Dilute Suspensions of Pusher Microorganisms

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