拟颗粒的物性统计及其在颗粒流体系统模拟中的应用
文献类型：学位论文
| 作者 | 李廷华 |
| 学位类别 | 硕士 |
| 答辩日期 | 2004 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 中国科学院过程工程研究所 |
| 导师 | 李静海 |
| 关键词 | 拟颗粒 压缩因子 运动粘度 沉降 |
| 其他题名 | Physical Properties of Pseduo-Particles and Their Application for the Simulation of Particle-Fluid Systems |
| 学位专业 | 化学工艺 |
| 中文摘要 | 本文致力于对拟颗粒的压缩因子、运动粘度等物性进行统计分析。拟颗粒模型是 结合分子动力学和直接模拟蒙特卡罗方法的优势而提出的一种粒子方法。其应用的空 间尺度小于计算流体力学网格而大于分子尺度。简单的分子物性推测方法难以正确地 应用于拟颗粒物理属性的确定，阻碍了基于拟颗粒模拟的定量分析。正确、真实地统 计测量拟颗粒物性参数将成为模拟与实验的纽带，也是完善拟颗粒模拟的重要基础。拟颗粒模型建立的微观机理表明了拟颗粒具有一些类似于分子尺度的特性。当拟 颗粒系统的速度分布满足Maxwell分布时，该系统达到平衡状态。在该平衡状态下，可以统计测量得到拟颗粒的平均自由程、压缩因子等物性与拟颗粒热速度、填充率的 关系。在外加力场作用下，通过统计拟颗粒在槽道流动中的平均流速可以得到拟颗粒 的运动粘度。对拟颗粒运动粘度结果的分析，揭示了该统计测量方法的合理性。另一方面，为了在实际系统的模拟中体现这些物性，还对拟颗粒与固体颗粒的作 用方式作了改进。现有模型以光滑刚性圆碟作为二维拟颗粒，在处理拟颗粒与固体颗 粒的作用时难以保证固体颗粒的边界无滑移。本论文对固体颗粒引入旋转参数，实现了拟颗粒与固体颗粒间较为真实的作用方式。作为模型改进的尝试，对单个固体颗粒 在流体中的沉降进行了二维模拟。固体颗粒逐渐沿着中心平衡位置沉降，沉降速度逐 渐达到恒定。模拟结果与现有实验及模拟吻合较好。作为拟颗粒模型的实际应用，本文对呼吸时口罩周围的流场进行了模拟。组成口罩的纤维材料被离散为一些固定的颗粒，拟颗粒所代表的空气通过大气控制区和鼻腔控制区的压差形成了流动。模拟结果再现了现有口罩在设计上的缺陷，改进的新造型口罩可以明显克服流场分布不均、局部流速高等缺点，降低了微尘穿透口罩的几率。 |
| 英文摘要 | This work is devoted to statistic analysis of physical properties of pseudo-particles, such as compressibility factor and kinematic viscosity. Pseudo-Particle Modeling (PPM) is a particle method proposed as a combination of Molecular Dynamics (MD) and Direct Simulation Monte-Carlo (DSMC). Different from macroscopic methods (two-fluid method, particle trajectory model, etc.), PPM discretizes the fluid into a large number of smooth and rigid pseudo-particles. From the point of view of simulations, the scale of pseudo-particle is between those of real molecules and of the computational cells in CFD simulations. Therefore, the physical properties of pseudo-particles can not be mapped from molecules, and should be measured statistically in simulations. These properties are very important because they provide a bridge between simulations and experiments, and will promote the development of PPM. Pseudo-particles are not molecules, but they possess some molecular characters. For instance, the equilibrium velocity distribution of the pseudo-particles is Maxwellian, and the physical properties of pseudo-particles, such as mean free path and compressibility factor, can be measured statistically. These properties are mainly functions of the thermal velocity and packing fraction of the pseudo-particles. In addition, the kinematic viscosity of pseudo-particles can be measured in the simulation of Plane Poiseuille Flow, driven by a constant mass force. Systematic measurement of these properties is conducted and the results are summarized in the thesis. At present, pseudo-particles are smooth rigid disks in two-dimensional PPM, which slip on the surfaces of solid particles. In this thesis, a more realistic interaction model is established by introducing a rotational variable for the solid particles, to restore the no-slip boundary condition while maintaining the conservation of kinetic energy. As a verification, the sedimentation of a single solid particle in a duct is simulated, which reproduces a reasonable particle track that following the centerline of the duct eventually. As an application, the model is applied to the simulation of the flow surrounding a facemask during the respiration process. The facemask is discretized into many static particles. The air is driven by a constant pressure drop between the inlet and outlet regions, that is, the atmosphere zone and the nasal cavity zone. The flow field reproduced demonstrates the disadvantages of the current facemasks, such as heterogeneous flows and high local flow velocity, etc. An improved design is proposed and verified in simulations, which can protect people's health more effectively. On the other hand, the simulations also demonstrated the advantages of PPM in simulating complex flows. |
| 语种 | 中文 |
| 公开日期 | 2013-09-16 |
| 页码 | 74 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1394]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 李廷华. 拟颗粒的物性统计及其在颗粒流体系统模拟中的应用[D]. 中国科学院过程工程研究所. 中国科学院过程工程研究所. 2004. |
入库方式： OAI收割
来源：过程工程研究所
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