Taylor dispersion of elongated rods

Kumar, Ajay; Thomson, Stuart; Harris, Daniel M.

doi:10.1103/physrevfluids.6.094501

Cited by 14 publications

(7 citation statements)

References 47 publications

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“…For example, Kumar et al. (2021) used two alternative collision conditions for the IBM simulations of rods. One is assuming that the micro-swimmers are immediately aligned to the direction of the flow once the collision happens; another is assuming uniformly random collision angles.…”

Section: Figure 14mentioning

confidence: 99%

Gyrotactic trapping of micro-swimmers in simple shear flows: a study directly from the fundamental Smoluchowski equation

2022

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Thin phytoplankton layers with vertically compressed structures found in stratified lakes and coastal water bodies have been a hot-spot in marine science and fluid mechanics. Although extensive efforts have been made to explore gyrotactic trapping as a possible mechanism, obvious inconsistencies remain there between the generalised Taylor dispersion method and individual-based model. In this work, a study directly from the fundamental Smoluchowski equation is carried out on the gyrotactic trapping mechanism in representative simple shear flows. With no approximation made to the fundamental equation and applying a biorthogonal expansion to the local moments of the probability density function, the evolution and steady state of the transport process are in good agreement with results of individual-based model, thus removing the gap between the continuum approach and individual-based model. The influences of strongly varying shear rate and boundary effect are reasonably scrutinised. The average swimming orientation with fixed local shear is highlighted as time-dependent rather than steady as previously assumed. The variations of characteristic time of the transient thin layer as functions of the flow intensity, gyrotaxis intensity and swimming ability are characterised. Sedimentation of the micro-swimmers is considered in some cases to reflect that micro-organisms are possibly negatively buoyant, with corresponding boundary conditions devised. A steady thin layer can be realised in the solution by adding a small settling speed to counteract the gravitactic focusing at the upper surface.

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Section: Figure 14mentioning

confidence: 99%

Gyrotactic trapping of micro-swimmers in simple shear flows: a study directly from the fundamental Smoluchowski equation

2022

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“…2013; Koens, Lisicki & Lauga 2017) or affecting Taylor dispersion in pipe flows (Taylor 1954; Kumar et al. 2021). Many relevant flows in microfluidic and other applications, such as Poiseuille or Couette flows, are approximately a shear flow at sufficiently small scales.…”

Section: Introductionmentioning

confidence: 99%

“…Slender particles in a pipe flow have been shown to have increased axial dispersion (Kumar et al. 2021) as well as a tendency to migrate across streamlines (Nitsche & Hinch 1997; Słowicka et al. 2012, 2013; Farutin et al.…”

Section: Introductionmentioning

confidence: 99%

Motion of asymmetric bodies in two-dimensional shear flow

Roggeveen

Stone

2022

J. Fluid Mech.

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At low Reynolds numbers, axisymmetric ellipsoidal particles immersed in a shear flow undergo periodic tumbling motions known as Jeffery orbits, with the orbit determined by the initial orientation. Understanding this motion is important for predicting the overall dynamics of a suspension. While slender fibres may follow Jeffery orbits, many such particles in nature are neither straight nor rigid. Recent work exploring the dynamics of curved or elastic fibres have found Jeffery-like behaviour along with chaotic orbits, decaying orbital constants and cross-streamline drift. Most work focuses on particles with reflectional symmetry; we instead consider the behaviour of a composite asymmetric slender body made of two straight rods, suspended in a two-dimensional shear flow, to understand the effects of the shape on the dynamics. We find that for certain geometries the particle does not rotate and undergoes persistent drift across streamlines, the magnitude of which is consistent with other previously identified forms of cross-streamline drift. For this class of particles, such geometry-driven cross-streamline motion may be important in giving rise to dispersion in channel flows, thereby potentially enhancing mixing.

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“…We also note that in individual-based dynamics, there exist various boundary interactions for Brownian swimmers (Jakuszeit, Croze & Bell 2019), such as specular reflection (Volpe, Gigan & Volpe 2014; Kumar et al. 2021), and different types of surface sliding models (Sipos et al. 2015; Spagnolie et al.…”

Section: Introductionmentioning

confidence: 92%

“…Potential-free methods (Peng & Brady 2020; Kumar et al. 2021) have also been developed to study suspension dynamics. In our study we consider suspensions in channels with height m (see table 1) and typical bacterial lengths of 1–2 m.…”

Section: Introductionmentioning

confidence: 99%

The interplay between bulk flow and boundary conditions on the distribution of microswimmers in channel flow

Maretvadakethope,

Hazel,

Vasiev

et al. 2023

J. Fluid Mech.

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While previous experimental and numerical studies of dilute microswimmer suspensions have focused on the behaviours of swimmers in the bulk flow and near boundaries, models typically do not account for the interplay between bulk flow and the choice of boundary conditions imposed in continuum models. In our work, we highlight the effect of boundary conditions on the bulk flow distributions, such as through the development of boundary layers or secondary peaks of cell accumulation in bulk-flow swimmer dynamics. For the case of a dilute swimmer suspension in Poiseuille flow, we compare the distribution (in physical and orientation space) obtained from individual-based stochastic models with those from continuum models, and identify under what conditions it is mathematically sensible to use specific continuum boundary conditions to capture different physical scenarios (i.e. specular reflection, uniform random reflection and absorbing boundaries). We identify that the spread of preferred cell orientations is dependent on the interplay between rotation driven by the shear flow (Jeffery orbits) and rotational diffusion. We find that in the absence of hydrodynamic wall interactions, swimmers preferentially approach the walls perpendicular to the surface in the presence of high rotational diffusion, and that the preferential approach of swimmers to the walls is shape-dependent at low rotational diffusion (when suspensions tend towards a fully deterministic case). In the latter case, the preferred orientations are nearly parallel to the surface for elongated swimmers and nearly perpendicular to the surface for near-spherical swimmers. Furthermore, we highlight the effects of swimmer geometries and shear throughout the bulk-flow on swimmer trajectories and show how the full history of bulk-flow dynamics affects the orientation distributions of microswimmer wall incidence.

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Taylor dispersion of elongated rods

Cited by 14 publications

References 47 publications

Gyrotactic trapping of micro-swimmers in simple shear flows: a study directly from the fundamental Smoluchowski equation

Gyrotactic trapping of micro-swimmers in simple shear flows: a study directly from the fundamental Smoluchowski equation

Motion of asymmetric bodies in two-dimensional shear flow

The interplay between bulk flow and boundary conditions on the distribution of microswimmers in channel flow

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