微游泳者引起的混合：以互信息为探针
Mixing induced by microswimmers as probed by mutual information
AI总结：
利用互信息作为全局混合效率度量，通过数值模拟二维squirmer模型，发现游泳者空间分布强烈影响混合，聚集抑制混合而无序增强混合，混合效率随squirmer参数非单调变化，且pusher优于puller。
摘要：
我们使用互信息作为混合效率的全局信息论度量，研究了微游泳者引起的流体混合。对于受限域中的二维squirmer模型，我们数值计算了游泳者产生的流动，并求解了示踪粒子在流体中输运的对流扩散方程。我们表明，游泳者的空间分布强烈影响混合，游泳者聚集抑制混合，而位置和取向无序增强混合。在固定能量耗散下，混合效率随squirmer参数非单调变化，最优有限值源于游泳者平移和偶极流生成之间的平衡。当包含流体动力学相互作用时，pusher优于puller。作为时间函数的互信息分三个阶段衰减：初始扩散主导阶段、中间对流增强阶段和最终由系统尺寸控制的弛豫阶段。我们的结果表明，互信息先前仅在简化模型系统中被验证为混合效率的度量，同样可以用于复杂流动。其应用揭示，微游泳者的混合受到强剪切流生成与实现跨流体域最优分散之间的权衡。
英文摘要：
We investigate fluid mixing induced by microswimmers using mutual information as a global, information-theoretic measure of mixing efficiency. For a two-dimensional squirmer model in a confined domain, we compute numerically the swimmer-generated flows and solve the advection-diffusion equation for the transport of tracer particles in the fluid. We show that the spatial distribution of swimmers strongly affects mixing, which is suppressed by swimmer aggregation and enhanced by positional and orientational disorder. At fixed energy dissipation, mixing efficiency depends non-monotonically on the squirmer parameter, with an optimal finite value arising from the balance between swimmer translation and dipolar flow generation. When hydrodynamic interactions are included, pushers outperform pullers. The mutual information as a function of time decays in three stages: an initial diffusion-dominated stage, an intermediate advection enhanced regime, and a final relaxation stage controlled by system size. Our results demonstrate that mutual information, previously validated as a measure of mixing efficiency only in simplified model systems, can equally be used in complex flows. Its application reveals that mixing by microswimmers is subject to a trade-off between the generation of strong shear flows and achieving optimal dispersion across the fluid domain.
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