Onset for Active Swimming of Microorganisms to Shape Their Transport in Turbulent Open Channel Flows

IF 4.6 1区 地球科学 Q2 ENVIRONMENTAL SCIENCES
Zi Wu, Li Zeng, Guangmiao Li, Zheng Gong, Jie Zhan, Weiquan Jiang, Mengzhen Xu, Xudong Fu
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引用次数: 0

Abstract

Research on active particles has primarily focused on transport in relatively weak flows, during which their active swimming plays a significant role. However, in natural or manmade waterways, the ambient flow velocity and water depth can be on the order of approximately 1 m/s and 1 m, respectively, generating turbulent diffusion that may be strong enough to potentially dominate the transport process, so that the active swimming might be negligible. In this paper, we propose a theoretical framework aiming at identifying the threshold at which the effects of active swimming become significant, under conditions of insufficient data for motion statistics of swimmers. While deriving the governing equation, we find that only the vertical component of the mean swimming has the potential to significantly influence the transport process. This manifests as the characteristic of inducing a non-uniform vertical concentration distribution, in competition with the mechanism of turbulent diffusion, which leads to a uniform distribution. We obtain the analytical solution for the vertical concentration distribution, with the key dimensionless parameter α representing the interplay between the active swimming and turbulent diffusion. The threshold is found to be approximately at the order of magnitude of α ∼ 0.1, below which active swimming is considered negligible. The theoretical predictions are validated by numerical simulations employing Direct Numerical Simulation and particle tracking methods. Applying the theory to two types of microorganisms transported under different flow conditions suggests that there are typical scenarios where the active swimming is negligible, and the swimmers can be treated as passive particles.
微生物在湍急明渠水流中主动游动以形成其运输的起始点
对活性颗粒的研究主要集中在相对较弱的水流中的传输,在这种情况下,活性颗粒的游动发挥了重要作用。然而,在自然或人工水道中,环境流速和水深可能分别约为 1 米/秒和 1 米,产生的湍流扩散可能足够强大,足以主导迁移过程,因此主动游动可能可以忽略不计。在本文中,我们提出了一个理论框架,旨在确定在游泳者运动统计数据不足的条件下,主动游动的影响变得显著的阈值。在推导控制方程时,我们发现只有平均游动的垂直分量才有可能对传输过程产生显著影响。这表现为诱导非均匀垂直浓度分布的特征,与导致均匀分布的湍流扩散机制形成竞争。我们得到了垂直浓度分布的解析解,其中关键的无量纲参数 α 代表了主动游动和湍流扩散之间的相互作用。我们发现阈值大约在 α ∼ 0.1 的数量级,低于这个数量级,主动游动就可以忽略不计。采用直接数值模拟和粒子跟踪方法进行的数值模拟验证了理论预测。将该理论应用于在不同流动条件下运输的两种微生物,结果表明,在一些典型的情况下,主动游动可以忽略不计,游动者可以被视为被动颗粒。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Water Resources Research
Water Resources Research 环境科学-湖沼学
CiteScore
8.80
自引率
13.00%
发文量
599
审稿时长
3.5 months
期刊介绍: Water Resources Research (WRR) is an interdisciplinary journal that focuses on hydrology and water resources. It publishes original research in the natural and social sciences of water. It emphasizes the role of water in the Earth system, including physical, chemical, biological, and ecological processes in water resources research and management, including social, policy, and public health implications. It encompasses observational, experimental, theoretical, analytical, numerical, and data-driven approaches that advance the science of water and its management. Submissions are evaluated for their novelty, accuracy, significance, and broader implications of the findings.
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