A Study on the Turbulent Diffusion of Matter and Small Particles by the Random Fourier Modes Method and Stochastic Model

该项目已按初步研究计划完成。目标(A)均匀平均速度三维湍流中羽流扩散场的数值模拟(L)首先，我们研究了网格湍流(无物体情况下)中一个点源产生的羽流扩散场。用随机傅里叶模法和两粒子随机模型进行了数值模拟。将随机傅里叶模法和快速扭曲理论相结合，对弹体周围的湍流场进行了数值模拟。利用模拟的湍流场，考察了点源羽流垂直入射圆柱体的特性，并用Prob…模拟了网格湍流中的反应混合层更多能力密度函数(Pdf)方法。目标(B)发展了用快速扭曲理论模拟复杂湍流流动的运动学方法，并将其应用于扩散场的模拟。主要综述了均匀湍流剪切流和轴对称收缩/膨胀流的快速扭曲理论的解析解。结果发现，在轴对称收缩/膨胀流动的情况下，存在时间稳定解，而对于均匀湍流剪切流，存在时间不稳定的解。进一步，根据直接数值模拟得到的物质颗粒的拉格朗日轨迹，估算了均匀各向同性湍流中的涨落标量统计。较少

This project has been put through according to the initial research plan. The progress and results of the research are summarized in the following,Object (A) Simulation of plume diffusion field around the body in the three dimensional turbulent flow with a uniform mean velocity(l) At first, we investigated the plume diffusion field from a point source developed in the grid-turbulence (in case of no body). The numerical simulations have been made by the random Fourier modes method and a Two-particle stochastic model. The simulation results obtained by both models show good agreements with the experimental results.(2) The turbulent field around the body has been simulated by combining the random Fourier modes method and the rapid distortion theory. By using this simulated turbulent field, the characteristics of a point source plume running perpendicularly into the cylinder have been examined.Furthermore, the reactive mixing layer in the grid-turbulence has been also simulated by the prob … More ability density function (pdf) method. From this time on, an application of this pdf method to the diffusion around the cylinder has been tried.Object (B) Development of kinematic method to simulate the complex turbulent flows by the rapid distortion theory, ant its application to the simulation of diffusion fieldsMainly, the analytical solutions of the rapid distortion theory for the homogeneous turbulent shear flows and axisymmetric contraction/expansion flows have been surveyed. Consequently, it was found that in cases of the axisymmetric contraction/expansion flows there exist the temporally stable solutions, but the solution for the homogeneous turbulent shear flows are temporally unstable.Besides the initial research plan, the diffusion fields of matter in the turbulent pipe flow has been investigated. Further, the fluctuation scalar statistics in the homogeneous isotropic turbulence were estimated from the Lagrangian trajectories of material particles obtained by the direct numerical simulation (DNS). Less