The interplay between bulk flow and boundary conditions on the distribution of microswimmers in channel flow
The interplay between bulk flow and boundary conditions on the distribution of microswimmers in channel flow
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DOI：
10.1017/jfm.2023.897
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发表时间：
2022-09
影响因子：
3.7
通讯作者：
Smitha Maretvadakethope;A. Hazel;B. Vasiev;R. Bearon
中科院分区：
文献类型：
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作者：
Smitha Maretvadakethope;A. Hazel;B. Vasiev;R. Bearon
摘要虽然以往对微泳者悬浮体的实验和数值研究主要集中在游泳者在体流和边界附近的行为上，但模型通常不考虑体流和连续介质模型中施加的边界条件的选择之间的相互作用。在我们的工作中，我们强调了边界条件对体流分布的影响，例如通过体流游泳者动力学中细胞积累的边界层或次峰的发展。对于Poiseuille流中稀释型游泳者悬架的情况，我们将基于个体的随机模型和连续介质模型得到的分布(在物理空间和方位空间)进行比较，并确定在什么条件下使用特定的连续介质边界条件来捕捉不同的物理场景(即镜面反射、均匀随机反射和吸收边界)在数学上是合理的。我们发现，晶胞择优取向的扩散依赖于剪切流(Jeffery轨道)驱动的旋转和旋转扩散之间的相互作用。我们发现，在没有水动力墙相互作用的情况下，当存在高旋转扩散时，游泳者优先接近垂直于水面的墙，而在低旋转扩散时(当悬浮物趋向于完全确定的情况)，游泳者优先接近墙的形状依赖于形状。在后一种情况下，对于细长的游泳运动员，首选的方向几乎平行于水面，而对于近球形的游泳运动员，首选的方位几乎垂直于水面。此外，我们强调了游泳者的几何形状和整个体流中的剪切力对游泳者轨迹的影响，并展示了体流动力学的完整历史如何影响微泳者壁面入射的方位分布。
Abstract 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.