Anomalous dispersion of microswimmer populations

Vennamneni, Laxminarsimharao; Garg, Piyush; Subramanian, Ganesh

doi:10.48550/arxiv.2212.01817

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“…For larger q, the exponent κ decreases. A recent preprint [32] reports an asymptotic value of κ = 4/3 1.33 for q → ∞; this value obtained using multi-scale analysis is close to the value of κ 1.5 obtained for the largest aspect ratio (q = 10) considered in our study. Finally, we observe that reducing the aperture delays the transition to the "active" regime.…”

Section: Discussionsupporting

confidence: 89%

Numerical modeling of dispersion of swimming bacteria in a Poiseuille flow

et al. 2023

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This paper reports a numerical study of the dispersion of bacteria modelled as active Brownian ellipsoids placed in a plane Poiseuille flow. The longitudinal (along the flow direction) and transverse (along the direction perpendicular to the plane of flow) macroscopic dispersion coefficients are determined from the analysis of a large number of trajectories and their scaling are studied as function of the Péclet number Pe.Three different regimes are observed: (i) at low shear rate, rotational diffusion associated to the swimming activity of the bacteria dominates and classical Taylor dispersion regime is observed. In this regime, the longitudinal dispersion coefficient scales like Péclet square. (ii) an intermediate "active" regime, where the shear induces a reorientation of the bacteria. This increases the longitudinal dispersion that scales as Pe 2+κ , with κ ranging between 1.5 and 2 for aspect ratio between 10 and 1. In this regime, the dispersion coefficient in the direction perpendicular to the plane of the flow decreases like log(1/Pe). (iii) a final "new" Taylor regime, where the diffusivity in the gap is set by the molecular diffusion coefficient. We also show that the "active" regime originates from the enhancement in the time taken by particles to diffuse across the channel gap. We further show that, decreasing the channel height delayed the transition to the "active" regime.

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Section: Discussionsupporting

confidence: 89%