TWO MODIFICATORY K-ε TURBULENCE MODELS FOR TURBULENT SWIRLING FLOWS

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｓｔａｎｄａｒｄＫ εｔｕｒｂｕｌｅｎｃｅｍｏｄｅｌｉｓｗｉｄｅｌｙｕｓｅｄｆｏｒｐｒｅｄｉｃｔｉｎｇｔｕｒｂｕｌｅｎｔｆｌｏｗｓｉｎｅｎｇｉｎｅｅｒｉｎｇａｐ ｐｌｉｃａｔｉｏｎｓ,ａｎｄｔｈｅｅｘｐｅｒｉｅｎｃｅｕｓｉｎｇｉｔｉｎｐｒａｃｔｉｃｅｈａｓｄｅｍｏｎｓｔｒａｔｅｄｔｈａｔｉｔｉｓｓｕｃｃｅｓｓｆｕｌｉｎ ｐｒｅｄｉｃｔｉｏｎｏｆｍａｎｙｔｕｒｂｕｌｅｎｔｆｌｏｗｓ,ｅｓｐｅｃｉａｌｌｙｔｈｅｓｉｍｐｌｅｓｈｅａｒｆｌｏｗ .Ｆｏｒｆｌｏｗｓｓｕｂｊｅｃ…     

推移质运动对清水和宾汉体泥浆湍流结构的影响

通过试验研究了清水湍流和泥浆湍流中加入推移质后时均流速分布、脉动强度、概率密度分布、相关系数、频谱密度分布等的变化.试验结果证明,清水和泥浆湍流中加入推移质后时均流速减小,时均流速梯度增大,脉动加强.泥浆过渡区湍流上部为层流,有流核,加入推移质后,上部层流转变为湍流,流核消失.分析证明,这是由于推移质运动增大了雷诺应力和时均流速梯度,因而增大了时均流动向脉动传递的能量的缘故,清水湍流中加入推移质后脉速概率密度分布偏离正态,偏态系数加大.泥浆湍流中加入推移质后相关系数降低,脉动的随机性增大.泥浆湍流的脉动能量集中于低频脉动.由于推移质也可以吸收低频脉动能来支持其运动,所以加入推移质后泥浆湍流的低频脉动能量降低,高频脉动能量增大.     

工业管路层流及湍流阻力特性区域的判别

对文[1]划分的湍流阻力特性区域界限数据用最小二乘法以指数曲线拟合,得出两区域界限的近似式,从而导出适用于管路水力计算三类基本问题的判别式,可以预先判明管内流动型态及湍流区域,避免繁复试算。     

数字图像处理技术在固-液两相流实验中的应用

本文开发研制了一个能直观描述固体颗粒在流场中的运动轨迹和速度矢量分布的人机交互数字图像处理系统软件，并把它用于固－液两相流的实验研究。结果表明，数字图像处理技术能够很好地用于分析悬浮颗粒在紊流中的跟随运动特征（速度分布、轨迹等），悬浮颗粒在紊流中的跟随运动取决于颗粒的粒径、密度和流体流动状况等因素。     

数字图像处理技术在固—液两相流实验中的应用

本文开发研制了一种能直观描述固体颗粒在流场中的运动轨迹和速度矢量分布的人机交互数字图像处理系统软件，并把它用于固－液两相流的实验研究。     

The inception cavitating flows over an axisymmetric body with a blunt head-form

The inception cavitating flows around a blunt body are studied based on flow visualizations and velocity field measurements. The main purpose of the present work is to study the incipient cavity evolution and the interplay between the inception cavitation and the local turbulent flows. A high-speed video camera is used to visualize the cavitating flow structures, and the particle image velocimetry(PIV) technique is used to measure the velocity field, the vorticity, and the Reynolds stresses under non-cavitating and inception cavitating flow conditions. It is found that the appearance of visible cavities is preceded by the formation of a cluster of micro-bubbles not attached to the body surface and in a hairpin-shaped vortex structure. During its evolution, the cavity moves downstream with a lower speed. The effect of the incipient cavity is significant on the local vortical structures but slight on the timeaveraged velocity distribution. The mean Reynolds stress distributions in the turbulent shear flow can be substantially altered by the incipient cavities. The presence of the incipient cavities can lead to the production of turbulent fluctuations.     

基于FLUENT的小尺度粗糙明渠紊流数值模拟

采用计算流体动力学软件FLUENT 对一小尺度粗糙明渠紊流进行数值模拟研究,得到了不同水深的垂向流速分布、壁面切应力以及摩阻流速值,并将数值计算结果与物理模型实验结果作了比较,发现两者符合得较好,从而验证了FLUENT 用于计算小尺度粗糙明渠紊流的有效性.由于计算机性能的限制,无法得到粘性底层和过渡层的"真实"流速分布,有待今后进一步研究.     

NUMERICAL SIMULATION OF STRESS-INDUCED SECONDARY FLOWS WITH HYBRID FINITE ANALYTIC METHOD

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｔｕｒｂｕｌｅｎｔｓｔｒｕｃｔｕｒｅｓｉｎｎｏｎ ｃｉｒｃｕｌａｒｄｕｃｔｓａｎｄｏｐｅｎｃｈａｎｎｅｌｓａｒｅｃｈａｒａｃｔｅｒｉｚｅｄｂｙｌｏｎｇｉｔｕｄｉ ｎａｌｖｏｒｔｉｃｅｓ .Ｔｈｅｓｅｖｏｒｔｉｃｅｓａｒｅｔｈ     

二维温差水流数值模拟

建立立面二维水动力学与水温耦合模型,用分步法求解流速和压力,采用大涡模型计算紊动应力和紊动扩散。对由温差引起的空腔流动进行了模拟,分析了流动特性与雷利数的关系。对水库冷水入流试验模型进行了模拟,并将计算结果与已有文献进行了比较,结果表明:无论是下潜流的厚度。还是纵向流速沿水深方向的变化都吻合得很好。     

NUMERICAL SIMULATION OF 3-D TURBULENT FLOWS IN A CUT-OFF VALVE AND ANALYSIS OF FLOW CHARACTERISTICS IN PIPE

1 .　INTRODUCTIONThevalvehasbeenplayinganimportantroleinthe pipeengineeringandisalsooneofmaincomponentsgeneratingtheheadloss .Becauseofthecomplexgeometry ,thedesignwasusuallyeval uatedempiricallyinthepast,whichcausesmuchenergyloss .Toreducetheenergyloss ,itisessen tialforadesignertoknowthedetailsofflowfieldinthevalvepipe .Recently ,withtheremarkableprogressintheComputationalFluidDynamics(CFD)andcomputerhardware ,itisexpectedthatCFDwillbecomeapowerfultoolinthedesignofvalve .Intheactual…     

稳定分层流动中湍流动量逆梯度输运的数值研究

本文采用RSM模式数值研究了温度和盐度的分层流动中湍流动量的逆梯度输运现象,并把计算结果和已有的实验结果进行了比较。计算主要考虑了分层强度、剪切率以及温度和浓度分层对湍流动量逆梯度输运的影响。由计算结果表明：在非剪切的分层流动中,温度分层,出现湍流动量的逆梯度输运。而盐度分层流动不出现湍流动量逆梯度输运现象。剪切分层流动中,剪切减小湍流动量的逆梯度输运。并且分层强度对温度分层比盐度分层影响大。     

SIMILARITY LAW OF TURBULENT FINE STRUCTURE

In engineering practical models designed by the gravity criterion,details relatingto turbulent fine structure are difficult to keep in similar.In this paper,similarity relations ofthe turbulent structure and its influences on turbulent lime-mean quantities are discussed in thecase of model flows satisfied the gravity similarity law.The fluctuating pressure acting on thefloor within free hydraulic jumps are measured for three scale models and compared with the the-oretical results.     

THE TURBULENT MODEL OF LIQUID-PARTICLE FLOWS AND ITS APPLICATION TO NUMERICAL PREDICTION OF OIL POLLUTION

Simulation of particle turbulent transport in present mathematical models of two-phase turbulent flows is algebraic model based on local following theory. The predicted results bythese models are not consistent with that of experiments available. The motion of two-phase flowis described by a unified model of multi-fluid in this paper. The two-fluid turbulent model oftwo-phase flow based on k-e equations for particles and fluid, and corresponding numerical thch-nique are both developed. The proposed model and the numerical technique are successfully em-ployed to numerical modelling for oil-water two-phase turbulent recirculating flow.     

MODELLING AND COMPUTATION OF UNSTEADY TURBULENT CAVITATION FLOWS

1. INTRODUCTION Cavitatating flows are important phenomena happened in industry setups and many under-water vehicles. It leads to performance losses and modifications of blade load when happened in machines, especially turbo-machinery. Nevertheless, cavit…     

紊流边界层脉动壁压研究

通过试验获得了紊流边界层脉动壁压信号，讨论了不同雷诺数条件下水流脉动壁压的统计特性，并对实测的脉动壁压进行了正交分解与低阶近似的研究．计算结果表明，紊流边界层的脉动壁压可用正交分解进行描述，其特征值随阶数的增加而减小，说明雷诺数越高，紊流中含能模态的激发越多．对脉动壁压进行低阶近似所须的阶数也与雷诺数的大小有关．     

淤泥质床面上减阻流动的紊动特征

本文对不同密度的淤泥质床面上水流运动的流速分布、减阻特征、紊流度、紊动猝发周期和能谱结构进行了系统的实验研究，并与刚性床面的结果进行了比较分析，结果表明：淤泥质床面具有减阻、增速、抑制紊流猝发产生和减小紊动耗散率的作用。     

LARGE EDDY SIMULATION OF FREE SURFACE TURBULENT CHANNEL FLOW WITH HEAT TRANSFER

1. INTRODUCTIONFreesurface turbulent flow exists widely in engineering. Due to difficulties in measurement and simulation, very little has been understood about the structures and transport mechanism of turbulence near the freesurface. Komori and Ueda…     

复杂剪切湍流场中湍流模型的研究

本文分析了双时间尺度湍流模型在复杂流场中的应用效果，并将双时间尺度概念和各向异性的Ｒｅｙｎｏｌｄｓ应力－应变关系相结合，对两个典型湍流场进行了数值模拟。结果表明，双时间尺度模型能较好地预测出复杂剪切流场中的平均物理量，较常规Ｋ－ε模型结果有很大改进。     

细颗粒悬沙浓度分布的影响因素分析

从颗粒运动的PDF(概率密度分布函数)输运方程出发建立颗粒相的质量、动量和脉动速度二阶矩方程。对明渠二维恒定均匀流，利用垂向动量方程导出了修正的泥沙扩散方程，表明颗粒脉动强度梯度、升力、有效重力和紊动扩散都影响悬沙运动。理论和数值分析了细颗粒泥沙的密度、粒径、浓度，挟沙水流的水深和剪切流速等因素对泥沙扩散系数和浓度分布形状的影响，并定量分析了细颗粒试验资料，表明传统扩散方程在粒径、剪切流速相对较大、水深和水沙密度比较小的流动中存在较大误差，需要修正。     

含植物明渠流动分区和特征尺度研究进展

植物是生态河流必不可少的要素之一。植物的存在,改变了水流的紊流结构。由于流动沿垂向具有较强的不均匀性,对于含植物明渠紊流统计特性的描述,至今未有公认的、统一的沿水深分布表达形式。因此,对含植物明渠流动分区和各区特征尺度的研究越来越受到重视。本文回顾了无植物明渠和含植物明渠流动分区及特征尺度研究的主要成果,重点对基于流速分布和紊流结构两种方法确定的分区和特征尺度进行了分析和总结。指出将涡结构与流动特性参数分布规律相结合进行流动分区,在各区确定合适的特征尺度,进一步探究分区界限及流动特征尺度的影响因素及具体影响,建立普适的紊流统计特性分布规律是今后含植物明渠紊流结构研究的重要内容和趋势。