弯槽湍流的直接数值模拟

本文采用直接数值模拟的方法对弯槽湍流进行了了研究，主要目的是研究流向曲率对湍流流动情况的影响。数值计算的雷诺数Rem-Umh/v=2800,其中Um为流向平均速度,h为弯槽的半槽宽，v为运动粘性系数。结果表明，弯槽凹壁和凸壁对湍流发展有不同的影响，凹壁使湍流加强而凸壁使湍流减弱。相干结构的分析表明凸壁附近上抛和下扫作用明显弱于凹壁，这是造成上述结论的原因。同时，弯槽中出现的Taylor-Gortlor涡造成了流动在展向的不均匀。     

湍流快速畸变理论及其应用

本文对湍流快速畸变理论进行了简单回顾，对其在无切变边界层、过山流动、脉动壁压、湍流大小尺度之间的相互作用等方面的应用进行了简要介绍。     

周期性振荡湍流的壁函数研究和数值实验

目前二阶湍流模式已被广泛运用于湍流的计算中，壁面和主湍流之的近壁区通常采用壁函数来近似计算，目前常采用的壁函数基于流动准稳态和充分发展等条件，对于周期性振荡湍流这类非定常湍流已不适应。本文基于周期性振荡湍流条件。推导了适用于周期性振荡湍流条件的近壁函数。采用Ｋ－ε模式，结合本文推导的周期性振荡湍流近壁函数，计算了一个二维直管周期振荡湍流流场，计算结果表明用本文推导的周期性振荡湍流近壁函数所得结果与     

用一种改进的κ—ε模型预测复杂湍流

Ｎａｇａｎｏ和Ｈｉｓｈｉｄａ提出了一个改进的κ－ε模型以计算壁湍流，并在简单流动的计算中得到验证，本文应用这一模型对突缩管内湍流，受限同轴射流和绕障碍物的二维渠道进行了数值预测，结果表明，引进流线曲率修正，该模型可以正确预测二维复杂流动的时均流速。     

明渠湍流结构对粒子运动跟随性影响综述

近年来大量学者通过室内试验、现场观测以及数值模拟等方法对明渠湍流中粒子的运动规律进行了深入细致的研究,逐步揭示了明渠湍流中粒子运动复杂性的本质和规律,并将成果应用于河流泥沙输移、河流地貌演变以及生态环境保护等多个领域。鉴于明渠湍流具有明显的分区效应,其湍流流速分布、分区结构组成以及相干结构分布特性等对水中粒子的运动过程均会产生显著影响,对水中粒子在明渠湍流结构中的整体运动规律、湍流结构内区以及外区的运动过程进行了总结;重点阐述了近壁区粒子运动规律的反常现象和原因,以及湍流结构中粒径、密度和Stokes数这3个影响粒子运动过程的主要因素。研究成果可为泥沙运动以及生态保护等研究及应用提供参考。     

壁湍流猝发和自由表面波破碎条件

应用G.K.Batchlor交界面流动的边界条件和小扰动稳定性理论,给出了壁湍流猝发、边界层边界的夹带和自由表面波的破碎条件和解释。发现这些现象可作为类比的相似流动来研究。当在边界层假设中保留p/n的边界层厚度的高阶小量(即p/n≠0),就可得到湍流的猝发现象。     

重力场下平板边界层内气液两相流动数值分析

通气减阻技术因具有降低能耗和环境污染小等效果,在工程领域内得到广泛关注。为研究重力场中气相在平板湍流边界层内流动演化过程及由此产生的减阻效应,该文耦合连续表面张力(CSF)的VOF多相流模型和标准k-?湍流模型,求解非定常RANS方程,对边界层内气液两相流动进行数值模拟。通过计算结果与实验结果的对比,验证了数值方法的有效性;进而对不同通气流量和来流雷诺数下,气泡当量直径、近壁区空隙率及流动减阻率进行定量分析。结果表明:减阻效应与近壁区空隙率密切相关;来流雷诺数和通气量的提高,均能增强减阻效应。     

直导叶几何参数对双向泵内流场及水力性能的影响

直导叶因其易于加工而广泛应用于轴流式叶片机械。为研究直导叶内的流动特性及其设计方法,以高比转速双向泵为研究对象,基于全结构化网格,采用SST k-ω湍流模型分析了加直导叶时泵内流动损失机理及直导叶几何参数对泵外特性和内流场的影响,总结了直导叶的设计方法。结果表明:直导叶弦长和叶片数增加会扩大发生流动分离的区域,形成大尺度回流;减小导叶-叶片轴向间距会增大直导叶进口冲角,加大分离强度,因此应在结构强度允许的情况下尽可能减小弦长及叶片数并适当增加轴向间距。研究结果可为轴流式叶片机械的直导叶设计提供一定参考。     

柔性壁对湍流边界层速度型的变形影响

本文从稳定性的观点出发，研究了粘弹性柔性壁对湍流边界层的影响。由柔性壁边办层稳定性问题的特征值计算结果发同，原刚性充边界层的速度型导致流固耦合系统不稳定，对数区上移后的边界层速度型却可以使耦合系统稳定，这说明，在没有水动力学不稳定发生的情况下，柔性壁会使湍流边界层中速度型的对数区上移。     

T型三通管内部流场数值模拟与结构优化

本文应用内部流场数值计算软件对进水管、出水管采用不同管径比的T型三通管道的湍流流动进行了分析计算,采用Segregated隐式解法应用标准K-ε双方程模型计算湍流粘度得到了三通管内部的流场分布,并对三通管道内流动的特性进行分析,得出三通管道湍流流动的计算结果。对比不同管径比的三通管道内流动的特性,得出了三通管道湍流流动的计算结果和具有较小水头损失三通的进水口、出水口的管径比。     

DIRECT NUMERICAL SIMULATION OF TURBULENT FLOW IN A STRAIGHT SQUARE DUCT AT REYNOLDS NUMBER 600

This article presents the direct numerical simulation results of the turbulent flow in a straight square duct at a Reynolds number of 600, based on the duct width and the mean wall-shear velocity. The turbulence statistics along the wall bisector is examined with the turbulent flow field properties given by streamwise velocity and vorticity fields in the duct cross section. It was found that the solutions of the turbulent duct flow obtained in a spatial resolution with 1.2×10⁶ grid points are satisfactory as compared to the existing numerical and experimental results. The results indicate that it is reasonable to neglect the sub-grid scale models in this spatial resolution level for the duct flow at the particular friction Reynolds number.     

对称突扩水流流态失稳和流场结构

对称突扩分离再附水流现象广泛存在于工程和生活中,流道突扩易产生局部水头损失、压力变化、结构振动、次生噪声等,对称突扩存在流场对称性失稳现象,如管道对称突扩等。然而,由于紊流的复杂性和量测技术的局限性,人们对其流动特性和流态演变规律认识仍然不足,有必要开展对称突扩流动的流场结构分析研究。本文基于物理模型试验和高精度图像粒子测速技术,模拟了不同雷诺数条件下（Re=539~48 911）对称突扩水流流动现象和精细流场结构,包含层流、过渡流和充分发展的紊流典型流态,随着雷诺数Re增加,流态从层流过渡到紊流,从对称到非对称分布,其流态发生对称性失稳,高雷诺数紊流时主流偏向一侧,流场结构相对稳定;揭示了突扩水流主流两侧形成的非对称分布的大尺度涡漩结构,其与流场对称性失稳有关联。     

表面糙率与明渠紊流猝发现象

采用流场综合分析法将流动显示与计算机图像处理相结合，在不同表面糙率的条件下重点研究紊流的猝发形态和特性.研究表明，表面粗糙度对明渠紊流拟序结构的特征有重要影响.猝发喷射角约为35～75度，随表面粗糙雷诺数增加趋于增大；喷射高度可达1/8水深；喷射尺度和清扫尺度均有随雷诺数增大的趋势.增大粗糙雷诺数明显增加了多头群体喷射现象，以致形成“喷射垫层”，清扫须在床面附近逐步深入推进；由于大雷诺数增加了群喷延续时间及清扫与喷射相持时间，无量纲猝发周期明显加大.分析还表明，在喷射迸发区域水体动能和紊流耗散率较床面附近提高了数倍.     

关于明渠水流的六区流态

用下临界Ｒｅｙｎｏｌｄｓ数、上临界Ｒｅｙｎｏｌｄｓ数、临界Ｆｒｏｕｄｅ数将明渠水流的流态划分为六区，即：缓层流、缓过渡流、缓紊流、急层流、急过渡流、急紊流，提出了六区流态划分图。并对明渠流与管流采用统一的流速公式问题，提出了看法。     

DEBRIS FLOW KINETIC CHARACTERISTICS UNDER NATURAL CONDITIONS

The study for debris flow kinetic characteristics can not be approached byexperiments due to their complexity and distransparency,etc.This paper is a picture of debrisflow kinetic characteristics based on the natural debris flow observation and experiments.Thekinetic characteristics of viscous debris flow are obtained by radar veloeimeter and ultrasoniclevel meter in jiangjia ravine.From those,the following are suggested:in natural channel,debris flow can be classified as three kinds of type:strong turbulent debris flow;turbulent debrisflow;weak turbulent debris flow:meanwhile the Reynolds number(Re)is chosen as an indexfor the classification.     

Numerical simulation of turbulent flow around a forced moving circular cylinder on cut cells

Fixed and forced moving circular cylinders in turbulent flows are studied by using the Large Eddy Simulation （LES） and two-equation based Detached Eddy Simulation （DES） turbulence models. The Cartesian cut cell approach is adopted to track the body surface across a stationary background grid covering the whole computational domain. A cell-centered finite volume method of second-order accuracy in both time and space is developed to solve the flow field in fluid cells, which is also modified accordingly in cut cells and merged cells. In order to compare different turbulence models, the current flow past a fixed circular cylinder at a moderate Reynolds number, Re = 3 900, is tested first. The model is also applied to the simulation of a forced oscillating circular cylinder in the turbulent flow, and the influences of different oscillation amplitudes, frequencies and free stream velocities are discussed. The numerical results indicate that the present numerical model based on the Cartesian cut cell approach is capable of solving the turbulent flow around a body undergoing motions, which is a foundation for the possible future study on wake induced oscillation and vortex induced vibration.     

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.     

Simulation of fine sediment transport in oscillatory boundary layer

Sediment transport and resulting morphodynamics take place at vastly different spatial and temporal scales. Bottom boundary layer dynamics is one of the most critical small-scale processes controlling sediment transport. However, it is very challenging as it involves highly nonlinear turbulent flow phenomenon that occurs at a scale as small as Kolmogorov scales. The unsteady nature of the flow forcing in the coastal environment, such as waves, is another important factor that further complicates the process. This paper aims to take a step to better understand wave-driven turbulent boundary layer and corresponding transport process. The problem of wave-driven sediment transport is simplified into fully developed oscillatory channel flow. Particles are assumed to be fine and dilute and hence they can be approximately considered as passive except gravitational settling with its settling velocity estimated from Stokes' law. Highly accurate pseudo-spectral flow solver has been employed and Direct Numerical Simulation (DNS) is carried out to resolve all scales of flow turbulence without sub-grid closure. Sediment concentration is then updated via mass conservation. Clear fluid simulation for intermittently turbulent condition (i.e., Stokes Reynolds number Re_Δ = 1000) is validated with earlier DNS results reported by Spalart and Baldwin [1989. Direct simulation of a turbulent oscillating boundary layer. Turbulent Shear Flows 6. Springer]. Fine sediment with dilute concentration is then added in the numerical simulation to study sediment suspension events under oscillatory flow. Suspension events are evaluated both qualitatively, by observing vortex structures, and quantitatively by the statistics of vertical fluxes. For fine particles and dilute concentration considered here, it is observed that particle phase is well-mixed in the boundary layer. Suspension is highly dependent on turbulent vortical structures at different wave phases.     

LARGE EDDY SIMULATION OF PARTICLE TRANSPORT IN FULLY DEVELOPED VERTICAL TURBULENT CHANNEL FLOW

Fully developed vertical turbulent channel flow with particle transport was investigated by use of Large Eddy Simulation (LES) approach coupled with dynamic the SubGrid Scale (SGS) model. It was assumed that the motion of each particle is followed in a Lagrangian frame of reference driven by the forces exerted by fluid motion and gravity under the condition of one-way coupling. The goal of this study is to investigate the effectiveness of the I.ES technique for predicting particle transport in turbulent flow and the behavior of particle-laden turbulent channel flow for three kinds of particles at different Stokes numbers. To depict the behavior of particle-laden turbulent channel flow, statistical quantities including particle fluctuation and fluid-particle velocity correlation, and visualization of the particle number density field were analyzed.     

黄土区陡坡径流水动力学特性试验研究

通过黄土水槽冲刷试验，初步研究了黄土区坡面径流的水动力学特性。陡坡径流的流态属于急紊流，且具有时空分异特征。随着坡度的增加，径流雷诺数Re和Darcy-Weisbach阻力系数f均呈先增后减的抛物线趋势。f与Re之间存在幂函数正相关关系，而f与弗劳德数(Fr)之间存在幂函数负相关关系。