Research On The Two-phase Flow With Cylindrical And Cubic Particles In The Channel And Pipe Flows

The thesis mainly includes three aspects.Extending the application of lattice Boltzmann method to concentrated particulate suspension.The lattice Boltzmann method(LBM) is a novel and effective method and can be applied in various fields of fluid mechanics.When applied to particulate suspension,LBM combines Newtonian mechanics for the solid particles with a discrete Boltzmann model for the fluid.The model proposed here combines the idea of Aidun with the idea of Ding.Specifically,the model incorporates particle dynamics,long-range and short-range hydrodynamic interactions, and particle collisions into LBM and applies to concentrated particulate suspension. As a test example,the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio were investigated by a 3D and 15-bits LBM model.Effects of non-linear physical factors on the rotational motion of a freely suspended non-Brownian particle in simple shear flow.Jeffery(1922) showed that a neutrally buoyant spheroidal particle suspended in an unbounded low-Reynolds-number simple shear flow executes a periodic orbiting motion whose precise trajectory and frequency depend on the particle aspect ratio and initial inclination.However,Jeffery's equations do not account for the effects of non-linear physical factors,such as inertial effects and wall effects.These effects disturb the Jeffery orbits,making it difficult to theoretically predict the particle motion where the aforementioned aspects play a role.Therefore,the effects of the two bounding walls and fluid inertia on the rotational motion of a freely suspended non-Brownian particle in simple shear flow have been investigated using the lattice Boltzmann method.Here, the wall effects are characterized by the flow confinement ratios,defined as the ratio of the channel height to the particle length.And fluid inertial effects are characterized by the shear Reynolds number based on the particle length. Orientation evolution of fibers in a suspension flow through complex channels.The orientation behavior of short fibers flowing through complex channels is a major concern in many physical and industrial processes,such as extrusion, injection,and compression molding.Therefore,the particle orientation distributions in the flows of particle suspensions through a slit channel containing a circular cylinder or with an abrupt expansion even in the concentrated regime were investigated.In the slit channel,particle length has the same order as the channel dimension.Interactions between fibers,between particle and channel walls and between particle and the obstacle make great influences on the particle orientation and flow property.All of these interactions were taken into account.These complex channels we consider here offer the possibilities of studying the behavior of the fibers in a variety of flows varying from simple shear and pure elongational flows,to more complex flows especially around the obstacle or just downstream of the expansion.Analyzing the flow in such geometry will beneficially contribute to reach a better understanding of flow properties in many important manufacturing processes to make composites.In order to design and control manufacturing processes that generate favorable particle orientation states,the effects of particle inlet orientation on particle orientation state were also explored.