孔隙裂隙介质内流体输运过程的格子Boltzmann建模与仿真

Fluid flow in pore-fracture media is usually observed in many fields, such as groundwater contamination, oil & gas engineering and so on. Compared with the fluid transport phenomena in normal porous media, the classic seepage mathematical model cannot describe the fluid flow in pore-fracture media any more because of the anisotropical characteristics. on the other hand,the pore-fracture media always exist micro-channels, these are also the difficulties for numerical simulation. The traditional numerical methods suffer from many bottlenecks such as the dealing with the complex boundaries, microscale effect is difficult to describe, massive computational cost and so on, while the bottlenecks are just the advantages of the lattice Boltzmann method(LB) which becomes popular in recent years. To this end, the study on the transport mechanism of flow in pore-fracture media is conducted using the LB method combined with parrell computational technique based on GPU in this project. The research topics include: developing efficient scheme for microscale boundary conditions; building LB model that can indicate the microstructure effects of pore-fracture media;analyzing flow mechanism and principles of flow in pore-fracture media; discussing the relations between microcosmic and macrocosmic flow in pore-fracture media. The project intends to further develop macroscopic numerical method based on the studies from microstructure mechanism. The study will provide an effective tool for practical engineering applications which related to this complex flow problems.

孔隙裂隙介质渗流规律的研究在地下水污染、油气工程等实际问题中有着广泛应用。与常规多孔介质内流体传输现象相比，孔隙裂隙介质因其各向异性的特点使得经典渗流模型的数学描述已不再适用，而且这类介质还存在许多微小孔隙和裂隙，这也是孔隙裂隙介质数值模拟的关键点和难点。传统数值方法常受制于复杂边界、微尺度效应、计算量大等困难。近年来发展的格子Boltzmann(LB)方法在处理这类困难时具有独特优势。本项目将结合LB这一先进数值模拟方法和GPU并行计算等高性能计算手段探索孔隙裂隙介质内流体的输运机理。主要包括：构建流体与固体作用的微观边界条件；发展能够反映孔隙裂隙介质内流体流动微观效应的宏观LB模型；分析流体在孔隙裂隙介质内的流动机理；探讨微观渗流与宏观渗流之间的联系。本项目从微观宏观相结合的角度出发，在微观机理研究的基础上，发展能够反映孔隙裂隙微观效应的宏观方法，可为研究实际工程问题提供新的有效手段。

孔隙裂隙介质内的流体流动通常是一个涉及热质传输的多场耦合系统，广泛存在于地下水污染、油气工程、化学工业等实际应用问题中。本项目采用近年来发展的格子Boltzmann(LB) 方法对孔隙裂隙介质内流体输运过程的机理进行研究。本项目基本按计划执行，主要内容包括（1）构建了描述多孔介质内不可压流体流动的单松弛格子Boltzmann模型，该模型的源项不含速度梯度，采用外力部分矫正的方法可以避免压力和速度的耦合，比已有的其它LB模型计算简单，在此基础上进一步发展了多松弛不可压D3Q14MRT模型和不可压D3Q18MRT模型，鉴于多孔介质内的流体流动通常会涉及到多场耦合问题，本项目在多场耦合LB方法的理论研究方面，针对不可压Navier-Stokes方程和对流扩散方程提出了相应的修正LB模型，使模型的稳定性得到了极大的改善；（2）建立了孔隙裂隙介质中介质孔隙率与介质微观结构之间的关系，可以较好的描述孔隙率随多孔介质固体颗粒形状、结构的变化；（3）设计了基于GPU平台的用于研究复杂多孔介质流动的高效格子Boltzmann算法，并实现了与之对应的GPU程序，为实现更大规模更高性能的LB模拟提供了必要的条件；（4）在上述算法和程序的基础上，对孔隙介质内的流体流动和传热问题进行了详细的数值模拟与分析。