| At present, a lot of phenomena and processes of fluid-solid two-phase flow havenot been well understood, the essential reason of that is the lack of understanding ofthe interaction mechanism between the fluid and solid phase. The investigation onthem was still mainly based on simple experimental observations and the empiricalformula constructed by the experimental data. Experimental and theoretical studieshave serious limitations, it is widely accepted that the numerical simulation can makeup some deficiencies in experimental and theoretical studies and has been adoptedas another powerful tool for researching.In this thesis, a Direct Numerical Simulation (DNS) model for turbulent was es-tablished firstly and investigation on the low Reτturbulent transportation in straightsquare duct was carried out. Then a coupled Computational Fluid Dynamics (CFD)and Discrete Element Method (DEM) model was established and used to simulatethe pneumatic conveying process and mortar conveying process in bends with cir-cular cross-section and chemical mechanical polishing process. The particle motionin the complex flow fields and wear situation caused by the collisions between theparticles and constrained surface were investigated, where the impact force betweenthe particles and constrained surface was used to represent the wear situation onthe walls. The current thesis can be divided into seven chapters:In the first chapter, the background of this study was introduced. The re-search contents and research methods of the fluid-solid two-phase flow were brieflyintroduced. Firstly, recent studies on the low Reτturbulent flow through a straightsquare duct were reviewed. Then the numerical investigations on pneumatic con-veying and mortar conveying process were introduced as well as the wear model onthe pipe wall. At last, recent research of the chemical mechanical polishing processwas reviewed with the main significance of this thesis summarized.In the second chapter, a Direct Numerical Simulation (DNS) model for singlephase turbulent flow was established, an efcient self-adaptive strategy for the ex-plicit time integration of Navier-Stokes equations was presented and a fourth orderdiscretization scheme was adopted. The Method of Manufactured Solutions wasused to verify the code while the length in streamwise was determined using two-point correlation. Then a numerical simulation of the turbulent transportation instraight square duct with low Reτwas carried out, obtained results were found in good agreements with those reported in the former literature. By doing this thecapability of the CFD code was verified and solid foundation was established for thefluid-solid coupling scheme.In the third chapter, a fluid-solid model based on the Eulerian-Lagrangianscheme was established, the numerical issues for the solid phase, namely the DiscreteElement Method, was detailedly described. A numerical test of the fluidized bedwas presented to demonstrate the capability of the current coupling scheme.In the fourth chapter, the pneumatic conveying process in bends with circularcross-section was investigated. First of all, a numerical simulation of the pneumaticconveying in a particular90elbow was carried out, the distribution of the pressureand velocity of the carrier fluid and the motion characteristics of the particles wereobtained. The impact forces on the inner and outer wall of bend were calculated anddrawn to stand for the wear situation on the walls. Obtained results showed goodagreement with those reported in the former literatures. Then the same methodwas used to simulate the pneumatic conveying process in multi-stage elbow. Thedistribution of fluid pressure and velocity in the multi-stage elbow were obtainedand the pressure drop was compared with that in90elbow. At last, the maximumimpact forces on the wall from the particle impact were analysed and the puncturepoint location was predicted. The results reported in this chapter can provide atechnical guidance for the optimizing design of the bend for pneumatic conveying.In the fifth chapter, the mortar conveying process in bends with circular cross-section was investigated. Firstly, the simulation of mortar conveying process in90elbow with circular cross-section was conducted. Obtained results such as pressureand velocity of carried fluid were compared with those from the pneumatic conveyingsimulation under the same working conditions, the diferences were discussed. Theimpact forces on the outer wall of bend were calculated and drawn to stand forthe wear situation, the statistic results were validated by comparing the numericalresults with an actual broken bend. Then the efect of the pumping velocity and bendorientation on the puncture point location have been discussed by conducting severalsimulations. At last, the simulation of the mortar conveying process in U-bend wascarried out with fluid pressure, velocity and wear situation investigated. The resultsreported in this chapter can provide a technical guidance for the optimizing designof the bend for mortar conveying.In the sixth chapter, the chemical mechanical polishing was investigated. Todemonstrate the capability of the PFC3D-CCFD software to simulate nano-multiphase flow, two verifications of numerical test were conducted with results compared withthose obtained from other’s experiments respectively. Then the simulations of thechemical mechanical polishing were carried out, the efect of the velocity of the padand wafer, solid fraction of the solid particles on the Material Remove Rate wasinvestigated, some phenomenon observed in the experiments were explained. Theresults reported in this chapter can provide a technical guidance for optimizing theart parameters in chemical mechanical polishing.Finally, the contents and innovations of this thesis were briefly summarizedwith drawbacks and future researches discussed. |
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