Hydrodynamic Instabilities of Active Jets
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arXiv
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| Main Authors: | , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866915504654909440 |
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| author | Vona, Marco Eisenmann, Isabelle Desprat, Nicolas Jeanneret, Raphaël Ishikawa, Takuji Lauga, Eric |
| author_facet | Vona, Marco Eisenmann, Isabelle Desprat, Nicolas Jeanneret, Raphaël Ishikawa, Takuji Lauga, Eric |
| contents | Using a combination of theory, experiments, and numerical simulations, we investigate the stability of coherent structures in a suspension of strongly aligned active swimmers. We show that a dilute jet of pullers undergoes a pearling instability, while a jet of pushers exhibits a helical (or, in two dimensions, zigzag) instability. We further characterise the nonlinear evolution of these instabilities, deriving exact and approximate solutions for the spreading and mutual attraction of puller clusters, as well as the wavelength coarsening of the helical instability. Our theoretical predictions closely match the experimentally observed wavelengths, timescales, and flow fields in suspensions of photophobic algae, as well as results from direct numerical simulations. These findings reveal the intrinsic instability mechanisms of aligned active suspensions and demonstrate that coherent structures can be destabilised by the flows they generate. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_16594 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Hydrodynamic Instabilities of Active Jets Vona, Marco Eisenmann, Isabelle Desprat, Nicolas Jeanneret, Raphaël Ishikawa, Takuji Lauga, Eric Soft Condensed Matter Biological Physics Using a combination of theory, experiments, and numerical simulations, we investigate the stability of coherent structures in a suspension of strongly aligned active swimmers. We show that a dilute jet of pullers undergoes a pearling instability, while a jet of pushers exhibits a helical (or, in two dimensions, zigzag) instability. We further characterise the nonlinear evolution of these instabilities, deriving exact and approximate solutions for the spreading and mutual attraction of puller clusters, as well as the wavelength coarsening of the helical instability. Our theoretical predictions closely match the experimentally observed wavelengths, timescales, and flow fields in suspensions of photophobic algae, as well as results from direct numerical simulations. These findings reveal the intrinsic instability mechanisms of aligned active suspensions and demonstrate that coherent structures can be destabilised by the flows they generate. |
| title | Hydrodynamic Instabilities of Active Jets |
| topic | Soft Condensed Matter Biological Physics |
| url | https://arxiv.org/abs/2509.16594 |