| Gas-solid two phase flow plays an important role in nature and many industrial pro-cesses. The studies on the interaction between the particles and the fluids are always the core issues of the gas-solid two-phase flow, such as the studies on the underlying mech-anism of the process and model prediction. The lattice Boltzmann method (LBM), as an novel technology of the Computational Fluid Dynamics (CFD), has become a useful tool for studying gas-solid two-phase flow. Because of a certain volume of computing grids are occupied by the particles, the computing time and memory consumption is particularly prominent. Therefore, the optimization of the LBM code becomes a very important issue. To optimize the code, we propose a new algorithm named the index algorithm. After that, a number of frontier issues in gas-solid two-phase flow are investigated. The main contexts are as follows:Firstly, a novel scheme, the index algorithm for the implementation of LBM is proposed. In the algorithm, a2D or3D problem can be reduced to a1D problem by an index (pointer) shift technique. After such step, one node needs only two neighboring nodes to finish its update by the fusion of collision and propagation. The memory consumption of the algorithm is almost the half of the conventional two-lattice algorithm. Compared to other existing optimization algorithms, the speedup of the present algorithm is2.3X for2D case and1.3X for3D case. Besides, the index algorithm’s cache behavior is the best among the existing algorithms. In addition, the algorithm can easily be implemented in the simulation of the gas-solid two-phase flow with complex boundaries. A simulation with1024particles is carried out and the computing speed is found to be20.19MLUPS using the Intel (R) Xeon (R) E5645the CPU.Secondly, in order to reduce the discretization error in the particle surface caused by the mesh discretization, we take advantage of the multiple-relaxation-time (MRT) model for LBM in the boundary treatment, and a proper set of relaxation parameters is given by comparing the simulation results of one particle in the stationary and moving stages.Thirdly, the particle sedimentations in the Newtonian fluid are investigated. The rela-tionship between the final particle Reynolds number and the states of motion for a single particle is analyzed. And then the effect of the channel width on the particle movement is studied. After that, the case for a pair of particles are also studied. Three kinds of motion state for the two particles are given, as well as their translational velocity, angular velocity and position changes.Fourthly, the movement of a single particle and a pair of particles in the power-law non-Newtonian fluid are studied. The relationship of the different non-Newtonian index and the particle trajectories. Analysis are also given on the changes of the vortex fields caused by the non-Newtonian index.Finally, the sedimentations of one particle in non-isothermal flow are studied. Two block ratios, which is defined as the ratio between the channel width and the diameter, are investigated. When the ratio is4, the Grashof number can be classified into several regimes by the the behaviour of the particle, the equilibrium position and the state of the trailing vortex. When the ratio changes to1.5, the walls of the channel have more effects on the behaviour of the particle, and a new phenomenon is discovered:the setting velocity of the particle becomes smaller with the increace of the Grashof number, and the velocity of the particle is0when the Grashof number is4083. Then the settling velocity of the particle changes its direction and the particle will move up when the Grashof number continues to increase. |
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