Inertia Drives a Flocking Phase Transition in Viscous Active Fluids

How fast must an oriented collection of extensile swimmers swim to escape the instability of viscous active suspensions? We show that the answer lies in the dimensionless combination R=ρv_{0}^{2}/2σ_{a}, where ρ is the suspension mass density, v_{0} the swim speed, and σ_{a} the active stress. Linea...

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Autores principales:	Rayan Chatterjee, Navdeep Rana, R. Aditi Simha, Prasad Perlekar, Sriram Ramaswamy
Formato:	article
Lenguaje:	EN
Publicado:	American Physical Society 2021
Materias:	Physics QC1-999
Acceso en línea:	https://doaj.org/article/f1a4819a896449f5bd32d91fa90991f3
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spelling	oai:doaj.org-article:f1a4819a896449f5bd32d91fa90991f32021-12-02T18:47:07ZInertia Drives a Flocking Phase Transition in Viscous Active Fluids10.1103/PhysRevX.11.0310632160-3308https://doaj.org/article/f1a4819a896449f5bd32d91fa90991f32021-09-01T00:00:00Zhttp://doi.org/10.1103/PhysRevX.11.031063http://doi.org/10.1103/PhysRevX.11.031063https://doaj.org/toc/2160-3308How fast must an oriented collection of extensile swimmers swim to escape the instability of viscous active suspensions? We show that the answer lies in the dimensionless combination R=ρv_{0}^{2}/2σ_{a}, where ρ is the suspension mass density, v_{0} the swim speed, and σ_{a} the active stress. Linear stability analysis shows that, for small R, disturbances grow at a rate linear in their wave number q and that the dominant instability mode involves twist. The resulting steady state in our numerical studies is isotropic hedgehog-defect turbulence. Past a first threshold R of order unity, we find a slower growth rate, of O(q^{2}); the numerically observed steady state is phase turbulent: noisy but aligned on average. We present numerical evidence in three and two dimensions that this inertia-driven flocking transition is continuous, with a correlation length that grows on approaching the transition. For much larger R, we find an aligned state linearly stable to perturbations at all q. Our predictions should be testable in suspensions of mesoscale swimmers [D. Klotsa, Soft Matter 15, 8946 (2019)SMOABF1744-683X10.1039/C9SM01019J].Rayan ChatterjeeNavdeep RanaR. Aditi SimhaPrasad PerlekarSriram RamaswamyAmerican Physical SocietyarticlePhysicsQC1-999ENPhysical Review X, Vol 11, Iss 3, p 031063 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Physics QC1-999
spellingShingle	Physics QC1-999 Rayan Chatterjee Navdeep Rana R. Aditi Simha Prasad Perlekar Sriram Ramaswamy Inertia Drives a Flocking Phase Transition in Viscous Active Fluids
description	How fast must an oriented collection of extensile swimmers swim to escape the instability of viscous active suspensions? We show that the answer lies in the dimensionless combination R=ρv_{0}^{2}/2σ_{a}, where ρ is the suspension mass density, v_{0} the swim speed, and σ_{a} the active stress. Linear stability analysis shows that, for small R, disturbances grow at a rate linear in their wave number q and that the dominant instability mode involves twist. The resulting steady state in our numerical studies is isotropic hedgehog-defect turbulence. Past a first threshold R of order unity, we find a slower growth rate, of O(q^{2}); the numerically observed steady state is phase turbulent: noisy but aligned on average. We present numerical evidence in three and two dimensions that this inertia-driven flocking transition is continuous, with a correlation length that grows on approaching the transition. For much larger R, we find an aligned state linearly stable to perturbations at all q. Our predictions should be testable in suspensions of mesoscale swimmers [D. Klotsa, Soft Matter 15, 8946 (2019)SMOABF1744-683X10.1039/C9SM01019J].
format	article
author	Rayan Chatterjee Navdeep Rana R. Aditi Simha Prasad Perlekar Sriram Ramaswamy
author_facet	Rayan Chatterjee Navdeep Rana R. Aditi Simha Prasad Perlekar Sriram Ramaswamy
author_sort	Rayan Chatterjee
title	Inertia Drives a Flocking Phase Transition in Viscous Active Fluids
title_short	Inertia Drives a Flocking Phase Transition in Viscous Active Fluids
title_full	Inertia Drives a Flocking Phase Transition in Viscous Active Fluids
title_fullStr	Inertia Drives a Flocking Phase Transition in Viscous Active Fluids
title_full_unstemmed	Inertia Drives a Flocking Phase Transition in Viscous Active Fluids
title_sort	inertia drives a flocking phase transition in viscous active fluids
publisher	American Physical Society
publishDate	2021
url	https://doaj.org/article/f1a4819a896449f5bd32d91fa90991f3
work_keys_str_mv	AT rayanchatterjee inertiadrivesaflockingphasetransitioninviscousactivefluids AT navdeeprana inertiadrivesaflockingphasetransitioninviscousactivefluids AT raditisimha inertiadrivesaflockingphasetransitioninviscousactivefluids AT prasadperlekar inertiadrivesaflockingphasetransitioninviscousactivefluids AT sriramramaswamy inertiadrivesaflockingphasetransitioninviscousactivefluids
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Inertia Drives a Flocking Phase Transition in Viscous Active Fluids

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