Hydrodynamic Interaction And Separation Mechanism Of Pairwise Capsules Flowing In Simple Shear Flows

Capsules are special structures formed by coating a micro-droplet with a very thin elastic material,which is widely found in nature,such as red blood cells,eggs,and follicles.Due to the great potential of the structure in drug slow-release and controlled release,the related industrial applications are numerous,and the capsule flow problem has become a research hotspot in the field of microfluidics.This thesis focuses on the flow phenomenon of symmetrical capsules in unbounded shear flow,and systematically investigates the flow behavior and separation law of paired capsules under the influence of flow intensity and initial position on the flow behavior and separation law of capsules by means of three-dimensional numerical modeling.The main work and results are as follows:Firstly,a three-dimensional numerical model of flow and deformation of symmetrically distributed couple capsules was constructed.Based on the assumption of symmetric distribution,the three-dimensional numerical model of fluid-solid coupling is constructed by combining boundary element and finite element method for fluid motion?fluid?and membrane deformation?solid?phenomenon;numerical implementation,and considering grid correlation and other factors.The comparison of the previous results shows that the three-dimensional model established in this thesis can reflect the physical problem more realistically.Secondly,the influence of initial position on the flow separation behavior of symmetric capsules was investigated,and the influence of initial distance in different directions on the flow separation behavior of couple capsules was studied in turn.The results show that in the shear flow,the symmetric capsules have an"attractive"effect in the horizontal direction?X direction?and a"repulsive"effect in the horizontal tangential direction?Y direction?.It is found that the symmetric capsules exhibit a special"reverse motion"phenomenon during the separation process,and the initial distance in the vertical direction?Z direction?is the key to the"reverse motion"of the microcapsules.Studies have also shown that the initial separation distance can directly affect the interaction between capsules,resulting in different flow separation behavior of capsules.Then,the influence of shear flow rate on the flow separation behavior of symmetric capsules was investigated.The results show that the change of external shear flow intensity can directly affect the deformation strength,flow trajectory and moving speed of capsule flow separation;the"reverse motion"phenomenon is also closely related to the flow intensity,and the lower the shear flow intensity,the more times of"reverse motion".Finally,the effects of the coupling effect of initial position and flow intensity on the flow separation behavior of symmetric capsules were investigated.Through a large number of numerical simulations,the key initial separation height?z₀?generated by the"reverse motion"phenomenon of symmetric microcapsules under different shear flow intensities is determined,and the coupling effect of flow intensity and initial separation distance on the number of"reverse motion"is determined law.The above results can provide some theoretical support for people to construct particles and cell sorting microfluidic chips.