Immersed Boundary-Lattice Boltzmann Method Simulation Study Of Particle Focusing In Microchannel Flow

In recent years,the microfluidic chip based on the principle of particle inertia focusing has been used to separate,purify and pretreat the biological microparticles,and obtaind great attention and research prospects.Through the simulation study of particles focusing,it helps to analyze the factors that affect the focusing,obtain the detailed information of the interaction between the fluid and the particle,and optimize the microfluidic chip.Therefore,it is of great theoretical and practical value to study the inertia focusing of particles in microchannel by numerical simulation.In this paper,the mechanism of particles focusing in microchannel is simulated by using immersed boundary-lattice Boltzmann method.Firstly,the lattice Boltzmann method is used to establish the periodic straight channel.After constructing the particle model,the immersed boundary method is used to simulate the interaction between the single particle and the flow field.The results show that the simulation method in this paper is very suitable for particle migration and focusing,and it can be proved by comparing the results of the research with the relevant scholars.The simulation results show that the method we used is suitable for the numerical simulations of particle migration and focusing.Through a large number of numerical simulations,this paper has the following conclusions and achievements:(1)In a single particle simulation,a rigid particle model was proposed and validated.In order to reveal the particle focusing behavior,the effect of particle size,deformability and Reynolds number on particles focusing was systematically studied.Increasing the size of the particles,strengthening the deformability of the particles,and increasing the Reynolds number will make the equilibrium position of the particles closer to the channel centerline.(2)In the multi-particle simulation,we found an interesting focusing phenomenon: binding focusing.A plurality of particles with different deformation rates migrate in the straight channel,and the final focusing equilibrium is in the same longitudinal position,and then the particles enter a new multi-particle focusing equilibrium state from the single focusing equilibrium state.In addition,the migration of multiple particles of different sizes in the channel is also affected by the binding focusing.During the course of the binding focus,the lateral migration velocity,the rotational angular velocity and the internal pressure of the particles change,and finally reach the equilibrium state.In addition,it is found by simulation that the number of particles and the size of the particles can also affect the multi-particle focusing equilibrium position.(3)Finally,based on the flow momentum discrete conservation equation,the hydrodynamic mechanism of particle focusing is studied and the focusing phenomenon is explained.Through the force analysis,it is proved that the dynamic equilibrium of flow field affects the whole process of particle migration,focusing and balance.