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许晓飞, 王炯哲, 张泽, 童松豪. 近壁剪切流中活性粒子运动特性实验研究和理论分析. 力学学报, 待出版. DOI: 10.6052/0459-1879-24-162
引用本文: 许晓飞, 王炯哲, 张泽, 童松豪. 近壁剪切流中活性粒子运动特性实验研究和理论分析. 力学学报, 待出版. DOI: 10.6052/0459-1879-24-162
Xu Xiaofei, Wang Jongzhe, Zhang Ze, Tong Songhao. Experimental study and theoretical analysis on locomotion characteristics of active particles in shear flow near wall. Chinese Journal of Theoretical and Applied Mechanics, in press. DOI: 10.6052/0459-1879-24-162
Citation: Xu Xiaofei, Wang Jongzhe, Zhang Ze, Tong Songhao. Experimental study and theoretical analysis on locomotion characteristics of active particles in shear flow near wall. Chinese Journal of Theoretical and Applied Mechanics, in press. DOI: 10.6052/0459-1879-24-162

近壁剪切流中活性粒子运动特性实验研究和理论分析

EXPERIMENTAL STUDY AND THEORETICAL ANALYSIS ON LOCOMOTION CHARACTERISTICS OF ACTIVE PARTICLES IN SHEAR FLOW NEAR WALL

  • 摘要: 活性粒子是一种具有自驱动能力的粒子, 自然界中的大肠杆菌是典型的活性粒子. 活性粒子在水体中的运动会受到流体剪切作用和边界约束的影响, 研究大肠杆菌在近壁剪切流中的运动规律有利于加深对活性粒子一般运动规律的理解. 基于微流控技术、高速显微图像采集技术和数字图像处理技术, 获得大肠杆菌在近壁剪切流中运动参数的量化信息, 考察流场剪切速率和大肠杆菌自驱动能力对大肠杆菌运动的影响, 从全局和局部两个角度研究大肠杆菌在近壁静止水体和近壁剪切流中的运动规律. 实验研究发现, 近壁静止水体中大肠杆菌呈圆周运动, 圆周运动角速度随大肠杆菌自驱动能力的提升而增大, 大肠杆菌平均直行速度和转向频率分别随悬浮液温度升高而增大和加快; 近壁剪切流中大肠杆菌随水体向下游运动的同时存在横向迁移, 横向迁移速度随剪切速率先快速增大后缓慢增大至最大值, 之后略微减小并最终趋于恒定, 转向频率则随剪切速率的增大和悬浮液的温度升高而加快. 构建并求解大肠杆菌运动的角速度模型, 对比大肠杆菌横向迁移速度的理论值和实验结果证明模型可靠性较好. 理论分析结果表明, 大肠杆菌运动方向与壁面的夹角随剪切速率的增大而缓慢减小, 而其在与壁面平行平面内的运动角则随剪切速率增大先快速减小后缓慢减小.

     

    Abstract: Active particles are particles with self-propelling ability, and Escherichia coli in nature is a typical active particle. The locomotion of active particles in fluids is influenced by fluidic shear flow and boundary constraints. Studying the locomotion of E. coli in shear flow near wall is beneficial for deepening the understanding of the general locomotion properties of active particles. Based on microfluidic technology, high-speed microscopic image acquisition technology, and digital image processing technology, quantitative information on the locomotion parameters of E. coli in shear flow near wall is obtained. The effects of shear rate of flow field and E. coli self-propelling ability on E. coli locomotion are investigated, and the locomotion properties of E. coli in stationary water and shear flow near wall are studied from both global and local perspectives. It is found that E. coli moves in a circular motion in stationary water near wall, and the angular velocity of circular motion increases with the increase of E. coli's self-propelling ability. The average swimming velocity and tumbling frequency of E. coli increase and accelerate with the increase of suspension temperature, respectively. In the shear flow near wall, E. coli undergoes lateral migration while moving downstream with the water flow. The lateral migration velocity first increases rapidly with the shear rate, then slowly increases to the maximum value, and then slightly decreases and tends to be constant. The tumbling frequency accelerates with the increase of shear rate and the suspension temperature. An angular velocity model for the locomotion of E. coli is established and solved. Comparing of the theoretical values and experimental results of the lateral migration velocity of E. coli, it can be proven that the model has good reliability. The theoretical analysis results indicate that the angle between the swimming direction of E. coli and the wall slowly decreases with the increase of shear rate, while its locomotion angle in plane parallel to the wall first rapidly decreases and then slowly decreases with the increase of shear rate.

     

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