Rapid Simulation Of Fluidized Reactors Based On The MP-PIC Method

Of numerical methods of gas-solid two-phase flows,the Multiphase Particle-In-Cell(MP-PIC)method,as a hybrid simulation method of particles and grids,is advantageous in both accuracy and efficiency.The discrete processing of particles gives it more advantages than the continuous method in the calculation and analysis of particle behavior.A small number of computational parcels are used to replace a large number of particles with the same properties and the solid stress model is used to simulate the collision between particles,which significantly reduces the computational burden and improves computational efficiency.Therefore,the MP-PIC method is adopted in this thesis to realize the rapid simulation of fluidized reactors,and the ways to further improve its simulation accuracy and efficiency are explored.In the MP-PIC method,the solid stress model represents the interaction between particles,while the influence of the mesoscale structure is not considered in the traditional model.In calculation,the positioning of discrete particles and the interpolation of particle properties on irregular fluid grids are complicated and time-consuming.These factors limit the application of the MP-PIC method in industrial simulation.To solve the above problems,in the model,this thesis develops a heterogeneous solid stress model considering the influence of mesoscale structure based on the Energy Minimization Multi-Scale theory;in the algorithm,particle calculation is simplified by grid mapping method;in the application,the program is paralleled and optimized,and the simulation of the industrial reactor is realized.The details are as follows:1)As the basis for the current research,a fully functional MP-PIC simulation program FOAM-PIC is firstly integrated based on an existing single-phase PIC code and the open-source software OpenFOAM.The simulation results of FOAM-PIC are consistent with that of the existing software,which verifies the correctness of FOAM-PIC.2)By introducing EMMS theory to quantify the mesoscale structure characteristics in gas-solid fluidization,a heterogeneous solid stress model is constructed.Simulation results of typical fluidized reactors show its superiority in precision and stability under the coarse grid and small parcel number.The sensitivity of simulation to solid stress model parameters is significantly reduced,which can greatly improve the computational efficiency.3)A precise and efficient grid mapping method is proposed based on the ideas of the particle grid method and the overlap mesh method.In this way,the gas phase and the solid phase can be calculated in different grids and then coupled,that is,the particles are tracked efficiently in a uniform Cartesian grid,and the precise mapping of two-phase flow field is established by considering the location and barycenter of each element in the two-phase grids segmented by another set of grid.The grid mapping method can greatly improve the efficiency of particle calculation and accelerate the simulation of fluidized reactors while maintaining computational accuracy.Simulation results of the MP-PIC with the grid mapping method of a circulating fluidized bed riser,a bubbling fluidized bed,and a turbulent fluidized bed are all excellent,which proves the feasibility and correctness of the method when dealing with complex structures and irregular grids.4)The FOAM-PIC program is parallelized and optimized,and the factors affecting the computational efficiency are also analyzed.The optimized program verifies its practicability in the simulation of an industrial scale MIP riser reactor and an HT-L coal gasifier.In the end,the main achievements of this research are summarized and further research directions in the aspects of the model,algorithm,and program implementation are prospected.