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

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 ofE. coliin 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 ofE. coliin shear flow near wall is obtained. The effects of shear rate of flow field andE. coliself-propelling ability onE. colilocomotion are investigated, and the locomotion properties ofE. coliin stationary water and shear flow near wall are studied from both global and local perspectives. It is found thatE. colimoves in a circular motion in stationary water near wall, and the angular velocity of circular motion increases with the increase ofE. coli's self-propelling ability. The average swimming velocity and tumbling frequency ofE. coliincrease and accelerate with the increase of suspension temperature, respectively. In the shear flow near wall,E. coliundergoes 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 ofE. coliis established and solved. Comparing of the theoretical values and experimental results of the lateral migration velocity ofE. coli, it can be proven that the model has good reliability. The theoretical analysis results indicate that the angle between the swimming direction ofE. coliand 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.