期刊
JOURNAL OF FLUID MECHANICS
卷 886, 期 -, 页码 -出版社
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2019.1055
关键词
low-Reynolds-number flows; propulsion; drops
资金
- European Research Council (ERC) under the European Union [714027]
- European Research Council (ERC) [714027] Funding Source: European Research Council (ERC)
Active droplets swim as a result of the nonlinear advective coupling of the distribution of chemical species they consume or release with the Marangoni flows created by their non-uniform surface distribution. Most existing models focus on the self-propulsion of a single droplet in an unbounded fluid, which arises when diffusion is slow enough (i.e. beyond a critical Peclet number, Pe(c)). Despite its experimental relevance, the coupled dynamics of multiple droplets and/or collision with a wall remains mostly unexplored. Using a novel approach based on a moving fitted bi-spherical grid, the fully coupled nonlinear dynamics of the chemical solute and flow fields is solved here to characterise in detail the axisymmetric collision of an active droplet with a rigid wall (or with a second droplet). The dynamics is strikingly different depending on the convective-to-diffusive transport ratio, Pe: near the self-propulsion threshold (moderate Pe), the rebound dynamics is set by chemical interactions and is well captured by asymptotic analysis; in contrast, for larger Pe, a complex and nonlinear combination of hydrodynamic and chemical effects set the detailed dynamics, including a closer approach to the wall and a velocity plateau shortly after the rebound of the droplet. The rebound characteristics, i.e. minimum distance and duration, are finally fully characterised in terms of Pe.
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