Research On The Hydrodynamic Behavior Of Two-phase Flow With Self-driven And Cylindrical Particles

Particulate suspension flows exist widely in nature and industrial processes.In this paper,numerical methods are used to study the dynamics and kinematics of particles in Newtonian and non-Newtonian fluids.The first aspect includes two research points.Firstly,a model that combines the Lattice Boltzmann-immersed boundary method with the singularity distribution method is proposed to simulate a self-propelled particle swimming(exhibiting translation and rotation)in a channel.It is found that the velocity distribution induced by the self-propelled particle deviates from Maxwell distribution,and its velocity strongly depends on the location of singularities.Secondly,The hydrodynamic interaction between a self-rotation rotator and passive particles in a two dimensional confined cavity at two typical Reynolds numbers according to the different Newtonian flow features is studied.For the system of two particles,the passive particle gradually departs from the rotator although its relative displacement to the rotator exhibits a periodic oscillation at the lower Reynolds number.Furthermore,the relative distance between the two particles and the rotator's rotational frequency are responsible for the oscillation amplitude and frequency.For the system of three particles,the passive particle's velocities exhibit a superposition of a large amplitude oscillation and a small amplitude oscillation at the lower Reynolds number,and the large amplitude oscillation will disappear at the higher Reynolds number.The change of the included angle of the two passive particles is dependent on the initial positions of the passive particles at the lower Reynolds number,whereas the included angle of the two passive particles finally approaches to a fixed value at the higher Reynolds number.The second aspect is the study of self-propelled particles in power-law fluids using the Lattice Boltzmann-immersed boundary method.The study consists of three small research points.The first is about the hydrodynamic behavior of a squirmer swimming in power-law fluid.The swimming velocity,streamlines,vorticity,energy consumption and hydrodynamic efficiency of a Squirmer(the self-propelled particle)in the Reynolds number ranging from 0.0005 to 5 are studied.It is found that the swimming speed and efficiency of Squirmer with different swimming modes are affected by Reynolds number and power-law index in varying extent.The physical mechanism behind the performance of the Squirmer with different swimming modes is discussed.The second is about hydrodynamic properties of squirmer swimming in power-law fluid near a wall.The swimming behaviors of a Squirmer with different swimming modes under different power indexs are obtained.Four new swimming behaviors are found for the first time,and the causes of these swimming behaviors are analyzed.The influence of various initial conditions on the swimming behavior is discussed.It is found that only increasing the Reynolds number can change the swimming behavior of the Squirmer.The reason is that the increase of Reynolds number weakens the attraction of the wall.The third is about hydrodynamic interaction between a pair of swimmers in power-law fluid.The influence of power law index on the parallel and opposite direction swimming of a pair of Squirmers with the same swimming mode is studied.It is found that the collision process of a pair of Pullers is significantly different from that of a pair of Pushers.Parallel swimming Pushers attract each other while the Pullers first repel each other and finally turn into a "head-to-head" contact state.A pair of pushers moving in opposite directions are very easy to "lock" in a certain position,while a pair of Pullers always depart from each other after collision.With the increase of power index,the degree of difficulty of Squirmer's rotation increases synchronously in the process of interaction.The third aspect is to study the dynamics of cylindrical particles in the contraction flow of a second-order fluid by using the finite volume method and the fourth-order Runge-Kutta method.Firstly,the basic theories of second-order fluid control equation,cylindrical particle motion equation,coordinate system transformation and collision mode between cylindrical particles and particles are expounded.The effects of Stokes number,Deborah number,particle length-diameter ratio and contraction ratio on the spatial and orientational distribution of three-dimensional cylindrical particles in a certain range are analyzed.It is found that the influence of aspect ratio on the spatial and orientational distribution of cylindrical particles is weaker than that of Stokes number,Deborah number and contraction ratio.Generally speaking,along the flow direction,particles diffuse from the region near the wall to the center of the contraction flow field and the spatial distribution of particles changes from relatively uniform at the inlet to non-uniform at the outlet,and finally to relatively uniform at the outlet.The change of orientation distribution is monotonous,and the particles are gradually arranged along the flow direction.This study,on the one hand,can deepen the understanding of the hydrodynamic mechanism of microorganisms in the nature in the predatory and complex swimming environment,and contributes to the design of micro-swimming devices or micro-robots.On the other hand,it makes clear about the effect of Non-newtonian fluid on the dynamics of cylindrical particles,which plays an important role in promoting industrial processes.