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Population splitting of rodlike swimmers in Couette flow

Nili, H ; Sharif University of Technology | 2017

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  1. Type of Document: Article
  2. DOI: 10.1039/c7sm00293a
  3. Publisher: Royal Society of Chemistry , 2017
  4. Abstract:
  5. 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. © 2017 The Royal Society of Chemistry
  6. Keywords:
  7. Distribution functions ; Probability distributions ; Shear deformation ; Suspensions (fluids) ; Active suspension ; Discontinuous transition ; Finite fraction ; Flow orientations ; Monotonic behavior ; Salient features ; Self propulsion ; Steady-state behaviors ; Shear flow
  8. Source: Soft Matter ; Volume 13, Issue 25 , 2017 , Pages 4494-4506 ; 1744683X (ISSN)
  9. URL: https://pubs.rsc.org/en/content/articlelanding/2017/sm/c7sm00293a#!divAbstract