Lattice Boltzmann Simulation On The Self-organized Transport Of Particles In A Microchannel

In recent years,the manipulation method based on the self-organized transport of particles in micro fluid has been proven to be an effective technology to precisely manipulate particles,and has wide microfluidic applications in particle/cell separation,enrichment and detection.This new approach to control particles has attracted increasing interest in the field of inertial microfluidic systems due to its significant advantages,such as easy operation,good stability,no need for external field and so on.For a better design of the inertial microfluidic chips,it is of significant importance to fully understand the features and mechanisms under the self-organized transport of particles.Therefore,the three-dimensional direct numerical investigation on the self-organized transport of particles is conducted in this thesis.The detailed research contents and main results are summarized as follows.(1)Construction of the numerical model.Based on the immersed boundary-lattice Boltzmann method,a numerical model for liquid-solid two-phase flow is constructed,which can precisely reproduce the momentum exchange between the liquid and particle.This model uses two independent sets of grids for liquid and particle respectively,and can capture the movement of the liquid-solid interface effectively.Additionally,by introducing the minimum grid number to represent the thin film between the particle and channel wall,the oscillation of the particle in other simulations which is a purely numerical artefact is eliminated.Thus,the accurate simulation for a large particle traveling in a square microchannel and its surrounding micro flow field over a large range of Reynolds numbers become possible.(2)Investigation on the lateral migration of a single particle.By simulating the lateral migration of particles with different sizes in a square microchannel,the law for the particle equilibrium position along lateral direction is revealed:with the increase of Reynolds number,the particle equilibrium position shifts to the channel wall first and then moves inward.The turning point of this trend occurs in the range of Re=100?200,and tends to shift to a lower Reynolds number as particle size increases.In addition,to quantitatively study the influence of the particle on its surrounding flow,a critical length,L_c,which can be used to measure the range of influence of the particle,is defined.Through fitting L_c for particles with different sizes under different Reynolds numbers,a new correlation for the critical length L_c is proposed for the first time,which can be applied to guide the selection of computational length in simulation to eliminate the numerical error caused by the interaction between particles.(3)Investigation on the axial ordering of a particle pair.Firstly,the different dynamic behaviors of a particle pair ordered on the same side or on opposite sides are revealed through numerical reconstruction of the whole process of a particle pair's axial ordering.Compared with the lateral migration of a single particle,it takes much more time for a particle pair to form a stable axial ordered train.This feature is very helpful for the design of the microchannel length.Secondly,the effect of particle size and particle Reynolds number on the axial ordering is further investigated systematically.Numerical results show that there exists a range of particle Reynolds number during which the particles can form a stable axial ordered train.For a particle pair ordered on the same side,the equilibrium inter-particle distance along axial direction reduces with the increase of the particle size,and reduces first and then increases while particle Reynolds number increases.For a particle pair ordered on opposite sides,the equilibrium inter-particle distance along axial direction reduces with the increase of the particle size,and increases while particle Reynolds number increases.The above mentioned conclusions can be used to guide the design of inertial microfluidic chips.