Numerical Study On Gas-solid Two-phase Flow Based On The Lattice Boltzmann Method: Direct Numerical Simulation And Efficient Implementation

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 thecore 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 annovel technology of the Computational Fluid Dynamics (CFD), has become a useful toolfor studying gas-solid two-phase flow. Because of a certain volume of computing gridsare occupied by the particles, the computing time and memory consumption is particularlyprominent. 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 contextsare as follows:Firstly,anovelscheme,theindexalgorithmfortheimplementationofLBMisproposed.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 itsupdatebythefusionofcollisionandpropagation. Thememoryconsumptionofthealgorithmis almost the half of the conventional two-lattice algorithm. Compared to other existingoptimization algorithms, the speedup of the present algorithm is2.3X for2D case and1.3Xfor3D case. Besides, the index algorithm’s cache behavior is the best among the existingalgorithms. In addition, the algorithm can easily be implemented in the simulation of thegas-solid two-phase flow with complex boundaries. A simulation with1024particles iscarried 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 bythe mesh discretization, we take advantage of the multiple-relaxation-time (MRT) modelfor LBM in the boundary treatment, and a proper set of relaxation parameters is given bycomparing 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 singleparticle 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 motionstate for the two particles are given, as well as their translational velocity, angular velocityand position changes.Fourthly, the movement of a single particle and a pair of particles in the power-lawnon-Newtonian fluid are studied. The relationship of the different non-Newtonian index andthe particle trajectories. Analysis are also given on the changes of the vortex fields causedby the non-Newtonian index.Finally, the sedimentations of one particle in non-isothermal flow are studied. Twoblock ratios, which is defined as the ratio between the channel width and the diameter, areinvestigated. When the ratio is4, the Grashof number can be classified into several regimesby the the behaviour of the particle, the equilibrium position and the state of the trailingvortex. When the ratio changes to1.5, the walls of the channel have more effects on thebehaviour of the particle, and a new phenomenon is discovered: the setting velocity of theparticle becomes smaller with the increace of the Grashof number, and the velocity of theparticle is0when the Grashof number is4083. Then the settling velocity of the particlechanges its direction and the particle will move up when the Grashof number continues toincrease.