Research On Sedimentation Of Solid Particles In Fluids Through Direct Numerical Simulationson

The sedimentation of particle is one of the most important part of two-phase flowing, and it closely related with the development of modern industry.This present work is investigating sedimentation of solid particles in fluids via lattice Boltzmann-fictitious domain method.First, by two-dimensional numerical simulation, the present work studies on a single circular particle and multiple circular particles sedimentation characteristics in the Newtonian fluid. Started from the dynamic of the particles, the factors which are the influence from the wall, Reynolds number and particle density have been considered to have an effect on velocity of the sedimentation and the stress coefficient.Moreover, the difference between the particle sedimentation and flowing past cylinder has been analyzed quantitatively that drag coefficient of two model is not obviously different, but the difference of lateral force coefficient and St coefficient is more than bigger. Especially the lateral force coefficient, with increasing of the Reynolds number, the difference of the lateral force coefficient increase gradually.As to multiple particles, by changing the number of particle and the initial state of arrangement, the group of particles appear different form of settlement. In addition,Reynolds number is one of the key factors.Second, by using the power-law fluid model, the simulation of the sedimentation of single particle and the multiple particles in shear thinning fluid has been studied, and demonstrated the impact of power-law index on the sedimentation in two dimension.At the same time, the difference of the sedimentation characteristics between Newtonian fluid and non-Newtonian fluid has been compared. The result shows that the index of power law-fluid(n≤1) becomes smaller when lateral force coefficient becomes bigger. Drag coefficient decreases with the increase of Reynolds number,and there is minimum value near the critical Reynolds number of vortex shedding. In addition, the relationship of St coefficient and Reynolds number has been analyzed quantitatively.Finally, by using the method of three-dimensional numerical simulation, which the sedimentation of sphere particles in Newtonian fluid has been studied. Comparing the data of simulation from literature, this method has been proved validated. When the particles arrange series, the influence of the initial spacing of particles and Reynolds number on the sedimentation has been studied. And there is a comparison between the sedimentation of sphere and the circular particles. The result shows that sphere particles appear three kinds of similar pattern of the sedimentation which have been shown in two-dimension situation.