Study On Composite Boundary Effect In Micro Channel Based On Lattice Boltzmann Model

Fluid flow in micro channel is a common phenomenon in nature, and is encountered in various disciplines, e.g., electronic devices, micro-electromechanical-systems, aerospace industry, biochemical industry, etc. Therefore better understanding fluid flow in micro channel is of great significance.As the internal structure of the micro channel is very complex and the governing equation is nonlinear, some of the flow properties are difficult to be determined accurately with experimental techniques and theoretical methods. Improvement of computers and the subsequent development of computational fluid dynamics (CFD) methods have gradually made it possible to directly solve many complex fluid dynamic problems. But the general computation fluid dynamic application and development is restricted in the certain degree for grid accuracy and boundary stability.Lattice Boltzmann method (LBM) is one of such simplified approaches, which is based on microscopic criterion level. The hydromechanics macroscopic equation can be derived from lattice Boltzmann equation by Chapman-Enskog method. This method is easy to process micro flow problem with inter-surface dynamics and complex boundary. In a sense, the LBM may be considered as a "numerical experiment" with some advantages such as simple arithmetic calculations, suited for large-scale parallel computing, suited for handling multiphase flow with phase transition, suited for handling boundary, and especially suited for studying micro fluid flow problems. In this dissertation, we use the lattice Boltzmann method to study the composite boundary effect in micro channel. Our progress includes three parts:Introducing the lattice Boltzmann method origin, development and present research situation. Giving the derivation of the lattice Boltzmann equation from continue Boltzmann equation and the derivation of the Navier-stokes equation from lattice Boltzmann equation in detail by Chapman-Enskog and Taylor method. We also introduce the lattice Boltzmann model for binary mixtures proposed by Luo and Girimaji. discussing several kind of classical boundary condition in the lattice Boltzmann method application, including bounce back boundary, specular reflection boundary , extrapolation method, periodic boundary, two-dimensional pressure (density) and velocity boundary, and three-dimensional boundary treatment. For the micro channel simulation, we analyze the different boundaries, especially the composite boundary setting.We propose the composite boundary treatment, and study the influence of the composite boundary for the fluid flow in two-dimensional and three-dimensional micro channel, respectively. When the ratio of the composite boundary is near the golden section, the fluid oscillation is the most obvious phenomenon. We use lattice Boltzmann model for binary mixtures to simulate liquid-liquid mixing in a T-type micro channel with composite boundary. When the ratio of the composite boundary is near the golden section, we also find that the mixing effect of the species fluid comes to high-point.