近年来，我国水产养殖行业持续高速发展，已经成为全世界水产养殖第一大国，也是世界上唯一养殖水产品总量超过捕捞总量的渔业国家。水产养殖业的快速发展降低了天然水域水生生物资源的利用强度，满足了人们对水产品的需求。但伴随着集约化水产养殖技术的大规模推进，由于网箱密度与数量的增加，箱内水体的流场特性十分复杂，进而影响饵料物质与代谢废物的输运。同时由于养殖区饲料的粗放式投放以及抗生素的过量使用等不合理的措施，致使养殖水域面临着水体污染严重、养殖病害频发等一系列生态安全问题，制约了我国水产养殖业的可持续发展。网衣作为网箱的关键组成部分，是由一系列纵横交错的细圆柱体（网线）组成的多孔柔性小尺度结构，自身特殊的结构属性，致使网衣周围的流场特性和传质过程十分复杂。因此，对网箱的流动和传质过程精确模拟的关键在于网衣，平面网衣流场特性的研究是网箱整体水动力特性研究的基础。 本研究首先利用粒子图像测速-平面激光诱导荧光(PIV-PLIF)耦合同步测量技术，在室内循环水槽开展了平面网衣在恒定均匀流中的尾流特性及近区传质机制实验；然后基于开源软件OpenFOAM中的pisoFoam、scalarTransportantFoam求解器，开发自定义passiveScalarPisoFoam求解器，采用RANS湍流模型，利用多孔介质模型对网衣进行概化处理，控制方程的离散采用有限体积法进行，采用PISO 算法实现速度场和压力场之间的耦合，建立了模拟水流作用下平面网衣周围流场与浓度场的耦合数值模型。本研究得到的主要结论如下： （1）在同一来流速度下，网衣密实度越大，流速衰减越显著，这与前人相关研究中得到的结果相吻合；在同一密实度网衣条件下，来流速度越小，流速衰减越显著，并且流速衰减程度最大的点位越靠近网衣。网衣下游的紊流强度先增大后减小，然后逐渐趋于稳定。依据紊流强度峰值位置将其可分为紊流发展区与紊流衰减区。在紊流发展区，紊流强度横向分布对应于网衣结构呈现出锯齿状分布，其较大值出现在网线位置，而流速较大值出现在网孔位置。在紊流衰减区，二者横向分布规律逐渐趋于相同。与前人在风洞中开展的格网尾流实验研究相比，在水槽中开展的网衣尾流流场的非均质性程度更显著；紊流发展区的各向异性与网衣密实度呈现正相关关系，且尾流流场达到均质性与各向同性的位置更加偏向于下游位置。 （2）在三维水流条件下，保守物质流经网衣后时均浓度沿横向的分布呈现高斯分布，并表现出自相似性；时均浓度沿纵向分布取决于拍摄面相对网衣所在的位置，并受网衣尾流紊流发展过程控制。有网条件下的扩散羽发展过程受网目大小、网线直径以及投放源相对于每组网衣所处的位置等因素共同影响；网衣存在时阻碍了浓度的扩散。网衣尾流近区范围内，瞬时浓度的方差沿横向呈现单峰结构分布，沿纵向的分布沿程递减。 （3）数值计算结果与实验结果吻合很好，数值模拟的结果精度较高。模拟结果表明，利用多孔介质概化网衣的近似处理可以从整体上体现网衣的阻流效应，流速衰减系数与网衣密实度、来流速度都呈现负相关关系。浓度沿横向分布的数值结果呈现高斯分布，并在不同的断面之间表现出自相似性。对网衣下游浓度场的整体模拟结果表明，流速对扩散羽的羽宽影响更为显著，羽宽值与来流速度呈现负相关关系，即来流速度越小，横向扩散显著，因此羽宽越宽。在同一来流速度下，不同密实度条件下的羽宽差异不大，密实度较大的工况中羽宽值稍大于密实度较小的工况。 本研究通过物理实验与数值模拟相结合的方法，系统研究了网衣尾流及其主导的标量物质输移过程，以及高度空间异质性的尾流流场主导作用下标量物质扩散规律。为进一步研究双层、多层网衣及网箱整体在复杂水动力条件下的尾流特性和传质机制奠定基础，可用于指导水流条件主导的网箱养殖场近区水环境影响评价和环境容量评估。

In recent years, Chinese aquaculture has developed rapidly，and has become the largest aquaculture country in the word，and it is also the only fishery country in the world where the total amount of farmed aquatic products exceeds the total amount of fish caught. The rapid development of aquaculture has reduced the use of aquatic resources in natural waters and met the demand for aquatic products. However, with the rapidly development of intensive aquaculture technology, due to the increase in the density and quantity of cages, the flow field characteristic in the cage is very complex, which in turn affects the transportant of bait materials and metabolic wastes. Meanwhile, some aquaculture areas are facing with a series of ecological problems such as serious pollution and frequent breeding diseases due to the unreasonable measures such as the extensive release of feed in the culture area and the excessive use of antibiotics, which restricts the sustainable development of Chinese aquaculture industry. As a key component unit of the cage, the net is a porous flexible small-scale structure composed of a series of criss-crossed thin cylinders, which lead to the flow field characteristics and mass transfer process around the net are very complex. Therefore, the study of the flow field characteristics of the flat net is the basis for the study of the overall hydrodynamic characteristics of the cage. In this study, the experiments were conducted in a recirculating flume firstly, the measurements of simultaneous velocity and concentration field were taken by combined PIV and PLIF. Then develop a user-defined passiveScalarPisoFoam solver based on the pisoFoam and scalarTransportantFoam solvers in the open source software OpenFOAM. The RANS turbulence model and porous media model were used in numerical simulation. The finite volume method was used to discretize the governing equations. The PISO algorithm was used to realize the coupling calculation between the velocity field and the pressure field, and the flow field and concentration field around the plane net then were simulated with different incoming velocities and solidities. The main conclusions of this study are as follows: (1) At the same income velocity, with the solidity increases, the velocity decays more obviously, which is consistent with the results obtained in previous studies. At the same solidity, the flow reduction factor is negatively correlated with the income velocity, and the point where the flow velocity reduction factor is smallest is closer to the net. The turbulence intensity downstream of the net increases at the beginning and then decreases and keep stable at the end. Based on turbulence intensity peaks, the distribution of turbulent intensity alone x direction can be divided into turbulent development region and turbulent decay region. In the turbulent development region, the lateral distribution of turbulence intensity exhibits a zigzag distribution corresponds to the net structure, with larger values appearing at the position after twine, which is in contrast with the lateral distribution of velocity. In the turbulent decay region, the lateral distribution of turbulent intensity and velocity gradually tends to be the same. Compared with the grid wake experiment conducted in the wind tunnel, the inhomogeneity of wake flow field around a net is more significant; The anisotropy of the turbulent development region has a positive correlation with solidity, and the positions where the wake flow become homogeneity and isotropic are more close to the downstream position. (2) Under the three-dimensional flow condition, the lateral distribution of mean-average concentration after the passive scalar flows through the net exhibits a Gaussian profile self-similarity. The distribution of time-averaged concentration along the longitudinal direction depends on the position of the image window relative to the mesh, it is also influenced by the turbulent development process of the wake flow. The development of diffusion plume with a net is affected by size of the mesh, the diameter of the twine and the location of the source relative to each group of meshes; the net hinders the diffusion of concentration. In the near region of the wake flow, the variance of the instantaneous concentration shows a single peak structure distribution along the lateral direction, and the distribution along the longitudinal direction decreases constantly. (3) The numerical results agree well with the experimental results, and the results of the numerical simulation have a higher accuracy. The simulation results show that the porous media can reflect the blocking effect of the net as a whole, and the flow velocity reduction factor has a negative correlation with the incoming velocity and solidity. The distribution of the concentration along the lateral direction is consistent with the experimental results. The simulation results of concentration fields show that the velocity has a more significant effect on the plume width, the value of plume width has a negative correlate incoming velocity. At the same inflow velocity, the difference of plume width with different solidity is not obvious. In this study, the combination of physical experiments and numerical simulations is used to study the wake characteristics and the near field transport processes through a fishing net panel, which will provide a basis to further study the wake characteristics and mass transfer mechanism of double-layer, multi-layer netting and cages under complex hydrodynamic conditions, and also can guide the water environment impact assessment and environmental capacity assessment of the near-area cage farms dominated by water flow conditions.