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Population splitting of rodlike swimmers in Couette flow

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Abstract

We present a quantitative analysis on the response of a dilute active suspension of self-propelled rods (swimmers) in a planar channel subjected to an imposed shear flow. To best capture the salient features of the shear-induced effects, we consider the case of an imposed Couette flow, providing a constant shear rate across the channel. We argue that the steady-state behavior of swimmers can be understood in the light of a population splitting phenomenon, occurring as the shear rate exceeds a certain threshold, initiating the reversal of the swimming direction for a finite fraction of swimmers from down- to upstream or vice versa, depending on the swimmer position within the channel. Swimmers thus split into two distinct, statistically significant and oppositely swimming majority and minority populations. The onset of population splitting translates into a transition from a self-propulsion-dominated regime to a shear-dominated regime, corresponding to a unimodal-to-bimodal change in the probability distribution function of the swimmer orientation. We present a phase diagram in terms of the swim and flow Péclet numbers showing the separation of these two regimes by a discontinuous transition line. Our results shed further light on the behavior of swimmers in a shear flow and provide an explanation for the previously reported non-monotonic behavior of the mean, near-wall, parallel-to-flow orientation of swimmers with increasing shear strength.

Graphical abstract: Population splitting of rodlike swimmers in Couette flow

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Publication details

The article was received on 11 Feb 2017, accepted on 23 May 2017 and first published on 25 May 2017


Article type: Paper
DOI: 10.1039/C7SM00293A
Citation: Soft Matter, 2017, Advance Article
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    Population splitting of rodlike swimmers in Couette flow

    H. Nili, M. Kheyri, J. Abazari, A. Fahimniya and A. Naji, Soft Matter, 2017, Advance Article , DOI: 10.1039/C7SM00293A

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