物质输运广泛存在于自然界和工业生产的各个领域中。一些物质输运问题可能涉及多尺度、多物理场的强耦合。随着计算流体力学(Computational Fluid Dynamics)的快速发展，研究者可以利用数值模拟对复杂的物质输运问题进行定量研究。常见的物质输运依据其尺度可划分为宏观尺度下的物质输运和微纳尺度下的物质输运。宏观尺度下的物质输运问题通常涉及复杂结构中高速或高温条件下气体、液体和固体等多相之间的相互耦合作用。微纳尺度下的物质输运问题通常受到空间的限制涉及两相界面变形以及多物理场的耦合作用。本文使用数值模拟方法重点研究了宏观尺度下钠冷快堆的假想堆芯解体事故以及微观尺度下非均相催化反应中可变形纳米片对反应物输运的影响。研究内容包含以下三个部分：

实现了对假想堆芯解体事故的准确数值计算模型构建、全尺寸三维数值模拟以及全面的数据分析，研究了事故中的快堆堆内物质输运问题及其引起的快堆结构变形，重点考察了堆芯能量，旋塞结构，热屏蔽结构对假想堆芯解体事故的影响。

通过二维的双向耦合模拟考察了假想堆芯解体事故中泄漏通道入口压力与泄漏速度的关系，将液钠泄漏过程分为两个阶段——快速泄漏阶段和稳态泄漏阶段。同时，利用第一部分全尺寸三维数值模拟的结果给定各液钠泄漏阶段的初始边界条件对液钠泄漏各阶段进行了模拟，最终获得钠冷快堆假想堆芯解体事故中液钠的泄漏总量。

利用相关实验结果开展了对非均相催化反应中柔性纳米片被动摆动的数值模拟研究。依据纳米片构型不同，边界条件的不同分析了柔性纳米片被动摆动对非均相催化反应中反应物输运的影响。数值模拟的定量研究证明了当纳米片高度与间距之比为2:1时，非均相催化反应效率达到最高；本研究从力学角度加深了对非均相催化反应的理解，为设计自驱动化学催化反应器提供了独特的思路。

综上，本研究利用基于计算流体力学的数值模拟方法研究了宏微观尺度下流固耦合物质输运问题，为研究涉及多尺度、多物理场耦合的复杂物质输运问题提供了新的研究思路。

Mass transportation is widespread in nature and various field of industrial production. Some mass transport problems may involve strong coupling of multiple scales and multiple physical fields. With the rapid development of Computational Fluid Dynamics (CFD), researchers can carry out numerical simulation to study complex mass transport problems quantitatively. Common mass transport can be divided into mass transport at the macro-scale and mass transport at the micro-nano scale according to its scale. The problem of mass transport at the macro-scale usually involves the coupling of multiple phases such as gas, liquid and solid under high-speed or high-temperature conditions in complex structures. The problem of mass transport at the micro-nano scale is usually limited by space, involving the deformation of the two-phase interface and the coupling effect of multiphysics. In this thesis, the numerical simulations are used to investigate the hypothetical core disruptive accident of the sodium-cooled fast reactor at the macro-scale and the influence of the deformable nanosheets on the transport of the reactants in the heterogeneous catalytic reaction at the micro-nano scale. The research content includes the following three parts:

Accurate numerical calculation model construction, full-scale three-dimensional numerical simulation and comprehensive data analysis for the hypothetical core disruptive accident were realized. The mass transport problem in the fast reactor during the accident and the structural deformation caused by the accident were studied. The impact of the core energy, plug structure, and heat shield structure on the hypothetical core disruptive accident were investigated.

 Two-dimensional two-way coupling method was developed to investigate the relationship between the inlet pressure of the leakage channel and the leakage velocity in the hypothetical core disruptive accident. The liquid sodium leakage process was divided into two stages—the rapid leakage stage and the steady state leakage stage. At the same time, using the results of the full-scale three dimensional numerical simulation, the initial boundary conditions of each liquid sodium leakage stage were simulated for each stage of liquid sodium leakage, and the total amounts of liquid sodium leakage during the hypothetical core accident was then obtained.

Based on the corresponding experimental measurement, numerical simulations of passive swinging of flexible nanosheets in heterogeneous catalytic reactions were carried out. Based on the configuration of the nanosheets and the different boundary conditions, the effect of passive swing of the flexible nanosheets on the reactants transport in the heterogeneous catalytic reaction was analyzed. Numerical simulations have proven that when the ratio of nanosheet height to pitch is 2: 1, the efficiency of heterogeneous catalytic reactions reaches the highest. This research provides unique opportunities to design a proof-of-concept self-propelled catalysis based on a greater mechanistic understanding of heterogeneous catalytic reactions.

In summary, this study uses numerical simulations, fluid dynamics to study the mass transport problem based on fluid-solid interactions in macro scale and micro-nano scale,  presenting a new point of view to understand the complex mass transport problems that involve multiscale and multiphysics coupling.