Active matter invasion of a viscous fluid: Unstable sheets and a no-flow theorem.

  title={Active matter invasion of a viscous fluid: Unstable sheets and a no-flow theorem.},
  author={Christopher J. Miles and Arthur A. Evans and Michael J. Shelley and Saverio E. Spagnolie},
  journal={Physical review letters},
  volume={122 9},
We investigate the dynamics of a dilute suspension of hydrodynamically interacting motile or immotile stress-generating swimmers or particles as they invade a surrounding viscous fluid. Colonies of aligned pusher particles are shown to elongate in the direction of particle orientation and undergo a cascade of transverse concentration instabilities, governed at small times by an equation that also describes the Saffman-Taylor instability in a Hele-Shaw cell, or the Rayleigh-Taylor instability in… 

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