Fully Resolved Direct Numerical Simulation Technique And Its Application In Multiphase Flows

In the last three decades, the traditional Lagrangian point source method is the main method in the study of multiphase flows and many meaningful results are achieved. However, this method has its limitation, and some mutual interactions between the particle phase and the fluid phase can not be described correctly. Therefore, it becomes very important to develop new approaches in numerical study such as the so called fully resolved numerical simulation method.In this dissertation, a novel multi-direct forcing scheme with the immersed boundary method is proposed for the fully resolved simulation of gas/liquid-solid multiphase flows. Two novel algorithms with the immersed boundary method and the multi-direct forcing scheme are proposed by combining the pressure-velocity equations and the vorticity-velocity equations to solve the Navier-Stokes equations, respectively. Some cases based on stationary immersed boundary are analyzed, and the second order convergence in spare of the immersed boundary method with the multi-direct forcing scheme is validated. Under the effect of the multi-direct forcing, the velocity at the immersed boundary of particle can be forced to satisfy the no-slip velocity boundary condition very well. Considering the characteristics of moving particle, the immersed boundary method with the multi-direct forcing scheme is applied to solve multiphase flow with fully resolved. Through the analysis of moving characteristics of a single particle and a group of particles in two-dimensional and three-dimensional space, the multi-direct forcing with the immersed boundary method can be applied to study the multiphase flow accurately and effectively. Some micro-phenomena are presented and observed such as the DKT phenomenon, anomalous rolling, etc. In this dissertation, to solve the heat transfer problem between fluid and particle, a novel multi-direct heat source scheme with the immersed boundary method is proposed. The accuracy of the multi-direct heat source scheme is validated through some cases analysis. And a parallel algorithm is also proposed to increase the computing efficiency. Then the multi-direct forcing and multi-direct heat source scheme with the immersed boundary method can be applied to study the interaction between the particle (particle group) and fluid with fully resolved.The immersed boundary method can be applied not only to study the multiphase flow but also to the other basic problems. In this dissertation, the immersed boundary method with the multi-direct forcing scheme is applied to study the disturbed effect of the inflow on a stationary spherical particle. And the immersed boundary method with multi-direct forcing scheme is applied to simulate particulate flows past an aligned tube bank and particularly study the erosion of the tubes and the duct side wall. This study is meaningful for engineering application.