Fully Resolved Direct Numerical Simulation Of Gas-Solid Heat Transfer And Combustion Process

Coal combustion is the main technology for energy production in China. Meanwhile, it causes serious environmental problems. In the past years, the traditional Lagrangian point source method and the coal combustion model were widely used and has achieved many meaningful results. However, the detailed gas-solid two-phase combustion process and some mutual interactions between the particle phase and the fluid phase cannot be described correctly. So far, there are few researches about the fully resolved numerical simulation method which can handle complex momentum-energy-mass coupled multiphase combustion problems. Therefore, it becomes very important to develop new approaches in numerical study for multiphase combustion process.In this dissertation, a novel ghost-cell immersed boundary method is proposed to handle Dirichlet, Neumann and Robin boundary conditions in compressible flows. The case of flow over stationary circular immersed boundary is analyzed and the second order convergence can be observed for different kinds of boundary conditions. The ghost-cell immersed boundary method is also applied to simulate moving objects. Through the analysis of moving characteristics of a single particle in two-dimensional space, the capability of the present ghost-cell immersed boundary method for handling moving boundaries has been proved. Furthermore, laminar flow heat transfer problems are used to test the capability of the present method to handle heat transfer process with different boundary conditions. The compressible effect on the heat transfer process is then studied to illustrate the advantage and necessity of combining IB methods with a compressible flow solver.In the present work, the ghost-cell immersed boundary method is further implemented to describe the fully coupled momentum-species-energy transport problems with complex immersed boundary geometries in multiphase reacting flows. The new method is used to simulate the char combustion process in a laminar flow. Two heterogeneous reactions and one homogeneous reaction are taken into account. Stefan flow at the char particle surface and the radiation heat transfer process are also considered. The calculated char combustion rate, velocity field, temperature field and species distribution have proved the capability of the present method on handling multiphase combustion process.