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Two-dimensional phoretic swimmers: the singular weak-advection limits
Published online by Cambridge University Press: 10 March 2017
Abstract
Because of the associated far-field logarithmic divergence, the transport problem governing two-dimensional phoretic self-propulsion lacks a steady solution when the Péclet number $\mathit{Pe}$ vanishes. This indeterminacy, which has no counterpart in three dimensions, is remedied by introducing a non-zero value of
$\mathit{Pe}$, however small. We consider that problem employing a first-order kinetic model of solute absorption, where the ratio of the characteristic magnitudes of reaction and diffusion is quantified by the Damköhler number
$\mathit{Da}$. As
$\mathit{Pe}\rightarrow 0$ the dominance of diffusion breaks down at distances that scale inversely with
$\mathit{Pe}$; at these distances, the leading-order transport represents a two-dimensional point source in a uniform stream. Asymptotic matching between the latter region and the diffusion-dominated near-particle region provides the leading-order particle velocity as an implicit function of
$\log \mathit{Pe}$. Another scenario involving weak advection takes place under strong reactions, where
$\mathit{Pe}$ and
$\mathit{Da}$ are large and comparable. In that limit, the breakdown of diffusive dominance occurs at distances that scale as
$\mathit{Da}^{2}/\mathit{Pe}$.
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