Inertia Drives a Flocking Phase Transition in Viscous Active Fluids

Chatterjee, Rayan; Rana, Navdeep; Simha, Robert; Perlekar, Prasad; Ramaswamy, Sriraṁ

doi:10.1103/physrevx.11.031063

Cited by 16 publications

(11 citation statements)

References 96 publications

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“…This is best represented by the kinetic energy spectrum E k = 1 2 ûi (k)û i (k) , which measures the kinetic energy associated with differing scales characterized by the wavenumber k. A numerical study of the simplified active nematics, which neglects order variation and thus topological defects, suggested a universal scaling of the kinetic energy, E k ∼ k −1 at small wavenumbers [18]. While such a k −1 scaling is recently observed in a numerical study of active polar fluid in certain parameter regimes [31], numerical simulations of the full active nematics did not find such universal behavior [9,58,59]. Most recently, a combined theoretical and experimental study showed different scaling regimes depending on the external or internal dissipation mechanisms for microtubule-kinesin motor mixtures at oil-water interface, which represent a realization of two-dimensional active nematic material [60].…”

Section: Resultsmentioning

confidence: 99%

“…However, in many other realizations of active matter, for example swimming organisms in environmental flows [22] and artificial active spinner suspensions [23], the inertial effect becomes significant, and the Reynolds numbers are nonzero [13]. Recent studies have begun to reveal interesting impacts of inertia on self-propulsion of active particles and inertial effects on active turbulence [24][25][26][27][28][29][30][31]. It is shown that increasing the inertia of active particles can result in a transition from active turbulence to flocking in polar active matter [31].…”

Section: Introductionmentioning

confidence: 99%

“…Recent studies have begun to reveal interesting impacts of inertia on self-propulsion of active particles and inertial effects on active turbulence [24][25][26][27][28][29][30][31]. It is shown that increasing the inertia of active particles can result in a transition from active turbulence to flocking in polar active matter [31]. Moreover, using a one-fluid model of an active matter with hyper viscosity, or a piece-wise constant viscosity, it was found that above a certain Reynolds number active matter can manifest vortex-condensate formation [29,32] in analogy with the condensates in classical driven 2D turbulence, where inverse energy cascade results in the accumulation of energy at larger scales and condensate formation [33].…”

Section: Introductionmentioning

confidence: 99%

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Nematic order condensation and topological defects in inertial active nematics

2022

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Living materials at different length scales manifest active nematic features such as orientational order, nematic topological defects, and active nematic turbulence. Using numerical simulations we investigate the impact of fluid inertia on the collective pattern formation in active nematics. We show that an incremental increase in inertial effects due to reduced viscosity results in gradual melting of nematic order with an increase in topological defect density before a discontinuous transition to a vortex-condensate state. The emergent vortex-condensate state at low enough viscosities coincides with nematic order condensation within the giant vortices and the drop in the density of topological defects. We further show flow field around topological defects is substantially affected by inertial effects. Moreover, we demonstrate the strong dependence of the kinetic energy spectrum on the inertial effects, recover the Kolmogorov scaling within the vortex-condensate phase, but find no evidence of universal scaling at higher viscosities. The findings reveal new complexities in active nematic turbulence and emphasize the important cross-talk between active and inertial effects in setting flow and orientational organization of active particles.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nematic order condensation and topological defects in inertial active nematics

2022

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“…However, inertial relaxation can be much slower for larger active elements, including insects to animals and macro-sized artificial active matter like active granular particles, vibrated rods, vibrobots, active spinners [19,[21][22][23][24][25][26][27], and as a result, can significantly influence the emergent dynamics [10-12, 18-20, 32-39]. For example, inertia can lead to the disappearance of motility-induced phase separation [40][41][42] observed for over-damped ABPs [43][44][45][46] and taming down of the instability in active nematics [47]. Moreover, it results in a distinctive impact on the dynamics of active phase separation [48], spatial velocity correlations [49], and entropy production [50].…”

Section: Introductionmentioning

confidence: 99%

Exact moments and re-entrant transitions in the inertial dynamics of active Brownian particles

Patel,

Chaudhuri

2023

New J. Phys.

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In this study, we investigate the behavior of free inertial active Brownian particles in the presence of thermal noise. While finding a closed-form solution for the joint distribution of positions, orientations, and velocities using the Fokker–Planck equation is generally challenging, we utilize a Laplace transform method to obtain the exact temporal evolution of all dynamical moments in arbitrary dimensions. Our expressions in d dimensions reveal that inertia significantly impacts steady-state kinetic temperature and swim pressure while leaving the late-time diffusivity unchanged. Notably, as a function of activity and inertia, the steady-state velocity distribution exhibits a remarkable re-entrant crossover from ‘passive’ Gaussian to ‘active’ non-Gaussian behaviors. We construct a corresponding ‘phase diagram’ using the exact expression of the d-dimensional kurtosis. Our analytic expressions describe steady states and offer insights into time-dependent crossovers observed in moments of velocity and displacement. Our calculations can be extended to predict up to second-order moments for run-and-tumble particles and the active Ornstein–Uhlenbeck process (AOUP). Additionally, the kurtosis shows differences from AOUP.

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“…However, many-body interactions are highly complex, especially with nonlinear convective acceleration 21 . Lately, the importance of inertia effects in the self-organisation of active or driven particles has also been recognised and studied intensively [46][47][48][49][50][51] . Furthermore, the turbulent nature of pattern evolution of active and driven particles in a fluid has also attracted much attention 27,29,31,32,[52][53][54][55][56][57][58][59] , known as "active turbulence".…”

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confidence: 99%

Phase separation of rotor mixtures without domain coarsening driven by two-dimensional turbulence

et al. 2022

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Unlike in thermodynamic systems, phase separation can occur without a thermodynamic driving force in active systems. How phase separation of purely hydrodynamic origin proceeds is an intriguing physical question. To this end, we study the phase separation of a binary mixture of oppositely rotating disks in a two-dimensional (2D) viscous fluid at an athermal condition by hydrodynamic simulations, focusing on the inertia effect. At symmetric and off-symmetric compositions, phase separation forms the oppositely flowing bands and a circular rotating droplet in the disordered matrix phase. In both cases, phase separation creates the largest structure directly from a chaotic state without gradual domain coarsening, unlike in the thermodynamic and corresponding dry rotor mixtures. We show that this unusual behaviour results from the nonlinear convective acceleration, i.e., the inverse cascade phenomena characteristic of 2D turbulence. Our finding reveals nontrivial nonlinear hydrodynamic effects on the self-organisation of active/driven particles in a fluid.

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Inertia Drives a Flocking Phase Transition in Viscous Active Fluids

Cited by 16 publications

References 96 publications

Nematic order condensation and topological defects in inertial active nematics

Nematic order condensation and topological defects in inertial active nematics

Exact moments and re-entrant transitions in the inertial dynamics of active Brownian particles

Phase separation of rotor mixtures without domain coarsening driven by two-dimensional turbulence

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