Simulating Multiphase Reactive Flows With Lattice Boltzmann Method

Large Scale Computation (LSC) has been becoming more and more important in scientific studies and engineering applications with the development of science and technology, and is well recognized as a significant method in addition to the experimental and theoretical approaches. Fluid flows simulation is one of the most important and challenging branches of Large Scale Computing. Recently, the Lattice Boltzmann Method (LBM) has developed into a new tool for simulating fluid flows and modeling complicated physical phenomena. Unlike the traditional Computational Fluid Dynamics (CFD) methods based on macroscopic continuum equations, LBM is based on microscopic model or mesoscopic kinetics equations. Compared with the traditional CFD methods, LBM has many unique advantages, such as simple codes, easy implementation of boundary conditions, and fully parallelism. These features of LBM have attracted many scientists and engineers from various fields. Until now, the applications of LBM have achieved great success in multiphase flow, porous flow, suspension particle flow, magnetohydrodynamics, and biologically mechanics, etc. LBM has become an important method for computational fluid dynamics. However, there still exist some disadvantages in LBM, such as combustion simulation, treatment interactions between different phases on a non-uniform grid, the coupling in gas-solid flows. Little work has been done in these fields. In order to facilate the applications of LBM in our subject, I have conducted some related studies in this thesis. Firstly, we study the treatments of external force in LBM, and discuss their advantages/disadvantages. Owing to the resemblance between the treatment of external force and reactive source term in LBM, it is very important to understand how to handle the external force in LBM. But surprisingly, there is little work on this topic. Therefore, we will start our work from this issue. Second, we construct a lattice Boltzmann model to simulate gas-solid flows in the two-way coupling framwork. We do this by treating the gas phase and the particulate phase respectively, based on the divide and conquer principle in mathematics: the gas flow is modeled by LBM, while the particle motion is described by solving the Newton equation. This model is expected to have potential applications due to the advantages of the two-way coupling method, and the advantages of LBM is maintained completely in this model. In the third part, we propose a novel finite-difference Lattice Boltzmann Model with an external force. The heuristic method employed in this model can be extended to other LB model, such as the incompressible model using a pressure distribution function. Furthermore, we present the relationship between this finite Lattice Boltzmann Model and other models with an external force. Finally, we design a simple Lattice Boltzmann scheme for simulating low Mach number combustion. We get rid of the constraint in other Lattice Boltzmann Models, and firstly use a pure Lattice Boltzmann Model to simulate realistic combustion phenomena. Furthermore, this model has the same advantages as the standard Lattice Boltzmann models, such as good numerical efficiency, easy implementation on high performance parallel computers, without any additional limitations and computational costs. In addition, the model used here provides a new way for designing other Lattice Boltzmann models. We also discuss boundary treatment scheme of LBM because it will affect the numerical precision and stability. Although many studies have been done on this topic, most of them are only for isothermal flows. In our study, we find that boundary treatment schemes have an importanl influences in combustion simulation. In conclusion, this thesis has made some efforts to improve the applications of LBM in multiphase flows and reactive flows. Several new models are designed and some relevant problems are studied. In addition, various numerical tests are conducted to verify the performance of the models and methods. This work can serve as a base for the applications of LBM in our subject.