Analytical structure, dynamics, and coarse graining of a kinetic model of an active fluid

Tong Gao, Meredith D. Betterton, An Sheng Jhang, Michael Shelley

Research output: Contribution to journalArticle

Abstract

We analyze one of the simplest active suspensions with complex dynamics: a suspension of immotile "extensor" particles that exert active extensile dipolar stresses on the fluid in which they are immersed. This is relevant to several experimental systems, such as recently studied tripartite rods that create extensile flows by consuming a chemical fuel. We first describe the system through a Doi-Onsager kinetic theory based on microscopic modeling. This theory captures the active stresses produced by the particles that can drive hydrodynamic instabilities, as well as the steric interactions of rodlike particles that lead to nematic alignment. This active nematic system yields complex flows and disclination defect dynamics very similar to phenomenological Landau-deGennes Q-tensor theories for active nematic fluids, as well as by more complex Doi-Onsager theories for polar microtubule-motor-protein systems. We apply the quasiequilibrium Bingham closure, used to study suspensions of passive microscopic rods, to develop a nonstandard Q-tensor theory. We demonstrate through simulation that this BQ-tensor theory gives an excellent analytical and statistical accounting of the suspension's complex dynamics, at a far reduced computational cost. Finally, we apply the BQ-tensor model to study the dynamics of extensor suspensions in circular and biconcave domains. In circular domains, we reproduce previous results for systems with weak nematic alignment, but for strong alignment we find unusual dynamics with activity-controlled defect production and absorption at the boundaries of the domain. In biconcave domains, a Fredericks-like transition occurs as the width of the neck connecting the two disks is varied.

Original languageEnglish (US)
Article number093302
JournalPhysical Review Fluids
Volume2
Issue number9
DOIs
StatePublished - Sep 1 2017

Fingerprint

Coarse-graining
Kinetic Model
Suspensions
Tensors
Fluid
Tensor
Kinetics
Fluids
Alignment
Complex Dynamics
Defects
Hydrodynamic Instability
Active Suspension
Microtubules
Kinetic theory
Kinetic Theory
Computational Cost
Closure
Absorption
Hydrodynamics

ASJC Scopus subject areas

  • Fluid Flow and Transfer Processes
  • Computational Mechanics
  • Modeling and Simulation

Cite this

Analytical structure, dynamics, and coarse graining of a kinetic model of an active fluid. / Gao, Tong; Betterton, Meredith D.; Jhang, An Sheng; Shelley, Michael.

In: Physical Review Fluids, Vol. 2, No. 9, 093302, 01.09.2017.

Research output: Contribution to journalArticle

Gao, Tong ; Betterton, Meredith D. ; Jhang, An Sheng ; Shelley, Michael. / Analytical structure, dynamics, and coarse graining of a kinetic model of an active fluid. In: Physical Review Fluids. 2017 ; Vol. 2, No. 9.
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