湍流边界层近壁区相干结构起因的研究

利用流动稳定性理论中的一般共振三波的概念,提出了一种湍流边界层近壁区相干结构产生机理的理论模型。由此所得的相干结构的空间形态,展向尺度,传播速度等都与数值模拟所得结果相近。特别是计算了多数是不对称的各种流向涡对环量差的概率密度分布曲线,得到了与数值模拟结果相比基本满意的结果。     

用大涡模拟检验湍流模型

用大涡模拟方法对直方管内充分发展湍流运动的数值模拟，所建立的数据库可以用来检验湍流模型，本文中数据库被用来检验Ｄｅｍｕｒｅｎ和Ｒｏｄｉ文中所讨论的代数模型，并进行了讨论。     

湍流边界层近壁区单个相干结构的模拟 *

提出了湍流边界层近壁区单个相干结构的理论模型 .用数值模拟的方法研究了它们的演化 ,结果发现在很多方面它们与实验观测到的特性相符 .     

概率分布的实函数实现问题

基于一维随机变量,通过阐释概率分布实函数实现的内在本质,给出了概率分布实函数实现的一个充分必要条件,得到分布函数族及其连续性特征,揭示出概率论中分布函数定义所蕴含的合理性和深刻性.     

用子波谱分析壁湍流多尺度结构的能量传递

测量了壁湍流不同法向位置的流向速度.用子波变换研究湍流能谱,表明子波全局谱是Fourier谱按子波尺度加权平均的结果,高阶消失矩的子波变换能够表征湍谱的衰减特性;子波局部谱显示边界层内涡的变形、破碎等现象与边界层法向位置有关,含能涡结构呈多尺度分布,随着测点远离壁面,含能涡的尺度增大;在缓冲区出现更高频的小尺度含能涡,在外区能量集中在低频大尺度涡结构中,含能涡的频带变窄.     

应用谱理论研究压力脉动的湍流模式

本文应用谱分析理论研究了剪切湍流场中的压力脉动,包括功率谱、均方值等.通过对压力脉动Possion方程的Fourier变换,首先将压力脉动谱表示成速度脉动谱的形式.利用Navier-Stokes方程的形式解及准正态分布假设,可以进一步将压力脉动功率谱表达式中所包含的速度脉动的三阶相关与四阶相关表示成速度脉动的二阶相关（功率谱）.最后,引入高雷诺数流的速度脉动功率谱模型,导出了由湍动e0,耗散ε,雷诺应力-iuj>及时均速度梯度表示的压力脉动均方值的湍流模式,并同现有数据进行了比较.     

壁湍流外层周期扰动对内层脉动特性的影响

在湍流边界层外层施加正弦波扰动,扰动波明显影响内层的猝发平均周期,破坏内层的大尺度低频脉动,诱发较小尺度的高频脉动,减小内层的积分尺度,提高内层流动的总脉动幅值。     

分层剪切湍流大涡模拟的一种动力学亚格子尺度模型

基于Yoshizawa涡粘性模型提出了一种适用于热分层剪切湍流大涡模拟的动力学亚格子尺度 (SGS)模型 ,包括SGS湍流应力和湍流热通量模型 ,计算验证了该模型的正确性 .进一步采用大涡模拟方法和该动力学SGS模型研究了稳定分层和不稳定分层槽道湍流的湍流特性 ,以及湍流主要变量关联量的变化规律 .同时 ,根据计算结果 ,预测了热分层槽道湍流的临界Richardson数 ,与理论分析结果基本相符 .     

大涡模拟的代数模型及其应用

大涡模拟是近十多年来发展起来的湍流研究的重要手段。本文介绍了大涡模拟的基本思想,提出了大涡模拟的代数模型,并详细地讨论了模型的建立。并将它应用于平直槽道和弯曲槽道中湍流的数值模拟,计算的初步结果表明本模型是可行的,并有望在进一步改善后可用于较复杂湍流的数值模拟。     

近壁区Reynolds应力及湍能耗散率输运特性的理论模型 *

提出在湍流边界层的近壁区采用三维不稳定波来描述湍流相干结构 ,然后根据理论模型对Reynolds应力及湍能耗散率的输运特性进行系统的计算和定量的分析 ,并计算了平均速度分布 .所得理论结果与直接数值模拟结果符合较好 ,表明本文方法正确地体现了湍流边界层近壁区的物理实质 .这不仅有益于对湍流机制的了解 ,而且可能为湍流的近壁模型化开辟一条新的途径 .     

A formulation on large eddy simulation

This note presents a formulation on large eddy simulation with the idea motivated by Fourier series representation. A set of filtered equations are obtained.     

Effects of plane strain on inhomogeneous turbulence

The influence of the mean plane strain on the turbulence transportation is investigated by large eddy simulation (LES) in the shearless turbulence mixing layer. It is found that the mean strains enhance the turbulent fluctuations in the mixing region. Compression in the inhomogeneous direction can greatly increase the transport of turbulent kinetic energy by triple correlation terms, while stretching in the inhomogeneous direction decreases the turbulence transportation. The gradient diffusion models for turbulent transportation are evaluated and it is found that the intermittency consideration can improve the prediction ability of the gradient-type models for the triple correlation terms. Project supported by the Sino-French Laboratory in Beijing and the National Natural Science Foundation of China (Grant No. 19572041).     

偏斜来流对圆柱跨声速绕流的影响

采用大涡模拟方法数值研究了偏斜角为60°的偏斜圆柱跨声速绕流.基于非偏斜圆柱跨声速绕流的实验和数值研究工作,来流Mach数取为0.75,Reynolds数取为2×10₅.通过与相同参数的非偏斜圆柱跨声速绕流对比,分析了偏斜来流对柱体受力和流动特性的影响.由于偏斜来流的流动控制,偏斜圆柱的阻力比非偏斜圆柱的阻力减小高达45%,而振荡力仅受到较小的抑制.偏斜圆柱流场的可压缩性被弱化,激波和小激波消失,而整体流动的模态未改变.偏斜来流使得偏斜圆柱后的剪切层变得更为稳定,进而提升柱体背压.在剪切层的初始发展阶段,剪切层的扰动涡斜脱泻模态和快速动能衰减是偏斜圆柱剪切层更为稳定的两个主要原因.     

A dynamic subgrid-scale model for the large eddy simulation of stratified flow

A new dynamic subgrid-scale (SGS) model, including subgrid turbulent stress and heat flux models for stratified shear flow is proposed by using Yoshizawa’s eddy viscosity model as a base model. Based on our calculated results, the dynamic subgrid-scale model developed here is effective for the large eddy simulation (LES) of stratified turbulent channel flows. The new SGS model is then applied to the large eddy simulation of stratified turbulent channel flow under gravity to investigate the coupled shear and buoyancy effects on the near-wall turbulent statistics and the turbulent heat transfer at different Richardson numbers. The critical Richardson number predicted by the present calculation is in good agreement with the value of theoretical analysis     

Flow simulation past axisymmetric bodies using four different turbulence models

A comparative assessment is presented of three different versions of high-Re k- models of turbulence for simulation of the flow past the entire length of axisymmetric bodies: standard, Chen and Kim-modified, and RNG-derived versions. Comparisons show that the standard model with wall functions can predict the flow characteristics at least as accurately as the other two. Application of the low-Re Lam and Bremhorst model further improves the predictive capability of wall-related quantities by removing the need for wall functions.     

An improved dynamic subgrid-scale model and its application to large eddy simulation of stratified channel flows

In the present paper, a new dynamic subgrid-scale (SGS) model of turbulent stress and heat flux for stratified shear flow is proposed. Based on our calculated results of stratified channel flow, the dynamic subgrid-scale model developed in this paper is shown to be effective for large eddy simulation (LES) of stratified turbulent shear flows. The new SGS model is then applied to the LES of the stratified turbulent channel flow to investigate the coupled shear and buoyancy effects on the behavior of turbulent statistics, turbulent heat transfer and flow structures at different Richardson numbers.     

概率母函数在求非负整值随机变量分布的应用

主要讨论概率母函数法求解古典概率问题的应用,以及某些非负整值的随机变量的分布.