Three-dimensional Numerical Simulation Study Of The Motion Of Red-blood-cell Particle Based On Lattice Boltzmann Method

Lattice Boltzmann method has become one of the popular computer simulation methods because of its simple,easy to handle complex boundary and easy to parallel computing,and it has been widely used in the simulation of particle two-phase flow,multiphase flow,thermal flow and other complex fluids.The momentum exchange method which satisfies Galileo invariance is accurate,efficient and easy to be programmed.It does not need the complex boundary integral of traditional calculation methods,and has a very good simulation effect on fluid-structure coupling problems.The movement of red blood cell particles in fluid is more complicated than that of spherical or ellipsoidal particles because of the special shape of double concave disk.At the same time,it is great significance for the blood flow and drug transport with the study about red blood cell particles.However,the current simulation algorithm for the movement of Red-blood-cell particles is mainly oriented to twodimensional or replaced by circle,and three-dimensional Red-blood-cell simulation algorithm is relatively lack,because it can not well calculate the force and rotation of Red-blood-cell.Therefore,based on lattice Boltzmann method,a three-dimensional motion model of red blood cell particles was established in this thesis,and the motion law of red blood cell particles in fluid was simulated and studied.The main work contents are as follows:1?In this thesis,a motion model of red blood cell particles based on lattice Boltzmann method is established.This model combines the momentum exchange method which satisfies Galileo invariant with the quaternion method which controls the rotation of particles,so as to solve the problems of inaccurate force calculation and rotation of three-dimensional red blood cells in fluid.In addition,this thesis proposes a judgment method to judge whether the particles of periodic trajectory reach the equilibrium position,which makes the judgment standard of particle steady-state quantifiable.In the visualization stage,an interface optimization algorithm based on clock coordinate sorting algorithm is designed,which can obtain smooth particle surface and solve the problem of boundary serration presented by the original interface data.2?In the numerical simulation of sedimentation,we studied the effects of the different blockage ratio and the density ratio of particle to fluid,and find a periodic sedimentation mode and two stable sedimentation modes finally.When the blockage ratio is large,the sedimentation mode of red blood cell particles changes from horizontal sedimentation mode to inclined sedimentation mode.With the increase of the density ratio of particles to fluid,the sedimentation mode changes from inclined sedimentation mode to horizontal sedimentation mode,and the time for red blood cell particles to reach stable state is obviously different in different sedimentation modes.It is worth noting that the oscillation mode can be observed in the larger blockage ratio and lower particle to fluid density ratio,which is a very delicate dynamic equilibrium state.3?The motion characteristics of red blood cell particles in Poiseuille flow by numerical simulation in this thesis.It is found that red blood cell particles and spherical particles both have lateral migration and equilibrium.However,when the fluid impinges on the side and concave surface of the red blood cell particles,two different migration trajectories can be obtained.The trajectories of the former are similar to those of the sphere,while the trajectories of the latter,due to its unique double concave surface,will produce periodic motion and non-uniform rotation in the whole process of lateral migration.In addition,with the increase of particle diameter,the amplitude of particle trajectory increases,the equilibrium position of particles moves to the center line of pipe,and the rotation period of particles becomes longer.However,there are only a few differences in the lateral migration trajectory of red blood cell particles under different particle density ratios.Compared with the sedimentation model of red blood cell which can be changed in sedimentation simulation,the effect of density ratio on red blood cell movement is limited.Because the movement of red blood cell particles in Poiseuille flow is complex,a series of contour maps are used to depict the flow field around red blood cell particles in different postures in order to capture the details of the flow field changes.These research results are conducive to the in-depth understanding of the movement characteristics of red blood cell particles,the aggregation and sorting of particles and drugs in the tube,and the research of human blood circulation and drug transportation based on red blood cell particles.