有压管道双孔板过流流场的数值模拟

运用计算流体力学方法，通过k-ε湍流模型对有压管道双孔板过流流场进行数值模拟。结合GAMBIT物理造型和Fluent模拟计算，得到管道内压力、速度、流线分布图及沿程压力、速度变化曲线，同时获得消能系数与孔径比的关系曲线，计算结果与经验值符合良好。     

库水位下降条件下土石坝渗流场数值模拟

以某水库土石坝为研究对象,利用Geo-Studio软件中的Seep/W模块对上游不同水位条件下的稳态渗流场和不同库水位下降速率条件下的瞬态渗流场进行数值模拟,分析了坝体浸润线、压力水头、体积含水量和水力梯度的变化规律。结果表明,在稳态渗流中,上游水位越高,坝体浸润线也越高,截面流量越大,坝体的安全性越低;库水位下降对坝体临水侧渗流场影响较大,且坝体内自由水面下降存在明显的滞后现象;水位下降速度越快,压力水头、体积含水量和水力梯度的变化对上游坝坡的安全稳定越不利。     

高宽比对矩形方腔内流动及能量损耗特性影响的数值分析

该文采用笔者所发展的二阶分裂步有限元方法，结合大涡模拟技术，在对雷诺数为100的三维方腔拖曳流动模拟的基础上，分析了不同高宽比条件下，矩形方腔内湍流流动及相应能耗场的变化。计算结果表明，矩形方腔高宽比对流场和能量损耗特性具有较强的影响，方腔内湍流对应涡系变化丰富，显示了上述方法在捕捉涡系及其时间演变过程方面具有较强的优越性。从计算结果可以看出，方腔内湍流流动结构呈现竖轴环流和立面环流的规律，在相应的高宽比条件下方腔内流动形成相应完整的回流区。相应流动的能量损耗集中出现在大尺度涡变化丰富的区段，正是对应湍流流动局部阻力损失产生的主要原因。流动和能耗场随时间的变化表明，整个方腔内湍流流动过程呈现出拟周期流动的特性。     

大型沉井拖航多迎流角水阻力数值模拟

该文针对大型方沉井拖航过程中的水阻力计算问题,采用基于计算流体力学的方法,进行了不同流速和不同迎流角组合工况下沉井的拖航水阻力数值模拟。结果表明,大型方沉井的拖航水阻力随沉井拖航速度的增大而增加,且与速度的平方成一定正比例关系;沉井拖航速度对沉井所受压力分布情况影响不大,而迎流角是沉井所受压力分布重要影响因素;沉井的长宽比也是影响拖航阻力的重要因素之一;沉井内部吃水部分所受水阻力大小明显受到迎流角的变化影响,而且占总阻力比例最高可达15.85%,不可忽略。     

冷喷涂自由射流过程的数值模拟

在冷喷涂技术研究中，喷管内部及出口后的超音速射流流场直接影响喷涂效果，所以对该流场研究十分重要。通过建立二维数学模型，对超音速气-固两相流进行数值模拟。得到气体压力的分布，不同直径的颗粒在流场中速度、温度变化曲线，以及颗粒的存在对流场的影响。结果表明，颗粒直径在0.1～100μm范围内．粒径的变化对流场的影响较小。在简化模拟中，可以不予考虑。     

平面闸槽区湍流场的数值模拟

本文利用各向异性Ｋ－ε模型对典型的闸门槽流场进行了系统的数值研究，得到了与实验结果相符的压力分布曲线和速度场，以及合理的湍流特征量的分布曲线。     

不同压力速度耦合模式下水轮机三维CFD计算对比

为研究在水轮机数值计算中不同的压力与速度耦合模式对水轮机内流场的影响。对作为研究对象的水轮机进行全流道三维建模及CFD计算。分别在流道蜗壳、转轮、尾水管内设置测点,计算在设定工况下不同压力速度耦合的流场及测点压力脉动数据。分析结果表明:PISO与Simple压力速度耦合模式下流场速度场分布相似,压力分布差异巨大,PISO模式下压力脉动为高频,Simple模式下为低频,其中Simple模式计算与实际符合较好。     

角区湍流场的实验测量和数值模拟

本文首先对角区湍流场作了详尽的测量，包括平板壁面和翼型表面上的压力分布，角区流场在来流，绕流以及尾流共十个横截面上的平均速度，脉动速度，湍动能和Ｒｅｙｎｏｌｄｓ应力，然后应用拟压缩性方法，在曲线坐标系下求解Ｎ－Ｓ方程选取了Ｂ－Ｌ湍流模式，对角区湍流场进行数值模拟。最后把计算结果与实验结果进行了对比，二者符合较好。     

上海青浦城区西北片河网引清调水的研究

基于河道水体溶解氧浓度随时间变化的实测数据,得出了上海青浦城区西北片河网在不同季节下的引清调水频率;采用经过实际调水过程验证的数学模型,对7种边引边排工况下的河网内水流运动进行了数值仿真,获得了每种工况下的水流速度场分布。以水流速度场模拟结果为基础,分析了现有水利设施条件下青浦城区西北片河网内水体的流动性,进而提出了为实现河网水体的流动自净功能应打通留水河和进行新的水利设施建设(如配置新的高流量水泵等)的建议。     

基于Eulerian-Lagrangian模型的粗颗粒管道输送数值模拟

该文针对水平管道内较粗颗粒浆体无相变流动过程,利用Eulerian–Lagrangian模型,追踪颗粒运动状态,探究较粗颗粒浆体在管道输送时的动力学特性,分析管道阻力特性及其在不同工况下的运行稳定性。流域内速度分布、浓度分布及压力曲线等结果与经验公式和实验数据的对比验证结果表明:模拟结果与Wasp公式计算结果和RocoBalakrishnam的实验值吻合良好,仿真更完善地描述流域内的流动特性。此外根据颗粒在管道不同位置的流动稳定性、流态转变过程及临界沉积速度等关键因素进一步分析了颗粒的流动特性。     

FORCE REDUCTION OF FLOW AROUND A SINUSOIDAL WAVY CYLINDER

A large eddy simulation of cross-flow around a sinusoidal wavy cylinder at Re=3000 was performed and the load cell measurement was introduced for the validation test. The mean flow field and the near wake flow structures were presented and compared with those for a circular cylinder at the same Reynolds number. The mean drag coefficient for the wavy cylinder is smaller than that for a corresponding circular cylinder due to the formation of a longer wake vortex generated by the wavy cylinder. The fluctuating lift coefficient of the wavy cylinder is also greatly reduced. This kind of wavy surface leads to the formation of 3-D free shear layers which are more stable than purely 2-D free shear layers. Such free shear layers only roll up into mature vortices at further downstream position and significantly modify the near wake structures and the pressure distributions around the wavy cylinder. Moreover, the simulations in laminar flow condition were also performed to investigate the effect of Reynolds number on force reduction control.     

Prediction of oil-water flow patterns,radial distribution of volume fraction,pressure and velocity during separated flows in horizontal pipe

Flow of two immiscible fluids gives rise to variety of flow patterns,which influence transportation process.In this work,we present detailed analysis on the prediction of flow pattern maps and radial distribution of volume fraction,pressure and velocity of a pair of immiscible liquids through a horizontal pipeline by computational fluid dynamics(CFD) simulation using ANSYS FLUENT 6.3.Moderately viscous oil and water have been taken as the fluid pair for study.Volume of fluid(VOF) method has been employed to predict various flow patterns by assuming unsteady flow,immiscible liquid pair,constant liquid properties,and co-axial flow.From the grid independent study,we have selected 47 037 number of quadrilateral mesh elements for the entire geometry.Simulation successfully predicts almost all the flow patterns(viz.,plug,slug,stratified wavy,stratified mixed and annular),except dispersion of oil in water and dispersion of water in oil.The simulated results are validated with experimental results of oil volume fraction and flow pattern map.Radial distribution of volume fraction,pressure and velocity profiles describe the nature of the stratified wavy,stratified mixed and annular flow pattern.These profiles help to developing the phenomenological correlations of interfacial characteristics in two-phase flow.     

EXPERIMENTAL INVESTIGATION ON THE DRAG REDUCTION CHARACTERISTICS OF TRAVELING WAVY WALL AT HIGH REYNOLDS NUMBER IN WIND TUNNEL

Drag reduction experiments of the traveling wavy wall at high Reynolds number, ranging from 1.46×10⁶ to 5.83×10⁶ based on the free-stream velocity and the model length, were conducted. A suit of traveling wavy wall device was developed and its characteristics of drag reduction at high Reynolds number were investigated. The drag forces of the traveling wavy wall with various wave speeds (c) were measured at different wind speeds (U) in the FL-8 low-speed wind tunnel and compared with the drag force of the flat plate. The results show that the mean drag force of the traveling wavy wall decreases as the value of c/U increases, at different wind velocities, the values of c/U corresponding to minimal drag force of the traveling wavy wall are different, when the values of c/U are larger than 0.6, the mean drag forces of the traveling wavy wall are smaller than those of the flat plate, and the drag reduction can be up to 60%. The drag reduction effectiveness of traveling wavy wall is thus achieved. Furthermore, as the value of c/U increases, the traveling wavy wall can restrain the separation and improve the quality of flow field.     

高含沙泄洪水流的荷载特性试验研究

高含沙水流特性已有较多研究,但主要针对河道中的高含沙渐变水流开展的,而对高含沙河流高坝枢纽泄洪水流荷载特性的研究较少,本文开展了孔板消能工高含沙水流的时均压力和脉动压力特性研究。试验共研究了含沙量从0至300 kg/m~3,流速从1.78 m/s至3.73 m/s,共28组不同工况。结果表明:高含沙泄洪水流的时均和脉动压力的沿程分布规律与清水相同,但幅值变化规律存在差异,相同流速条件下时均压力幅值随含沙量的增加而增加,而脉动压力幅值受含沙量和流速条件的双重影响,随含沙量的增加呈现出先增加后减小的趋势;脉动压力概率密度分布符合正态;频率分布范围受水流条件影响随流速的增加而增加,其中低频分量随含沙量的增加而增加。根据试验结果,提出了高含沙泄洪水流荷载计算的修正方法,该方法对于高含沙枢纽的工程设计有重要参考价值。     

全自动鱼雷网式过滤器内部清水流场特性数值分析

采用Fluent软件中的Realizable k-ε湍流模型与多孔介质阶跃面对不同流量下全自动鱼雷网式过滤器的清水流场进行数值模拟.结果表明:数值计算中进、出口间水头损失同物理试验的吻合程度较高,选择的数学模型具有较高的准确性和可靠性.对比不同流量下的计算结果可知,流量不同时过滤器内速度分布规律相同,压强分布规律也相同,但流量越大,水头损失越大,滤网内外侧的速度差、压强差也就越大;过滤器内的速度和压强分布越不均匀,结构有待进一步优化.     

PIV analysis and high-speed photographic observation of cavitating flow field behind circular multi-orifice plates

Based on a self-developed hydrodynamic cavitation device with different geometric parameters for circular multi-orifice plates, turbulence characteristics of cavitating flow behind multi-orifice plates, including the effects of orifice number and orifice layout on longitudinal velocity,turbulence intensity, and Reynolds stress, were measured with the particle image velocimetry(PIV) technique. Flow regimes of the cavitating flow were also observed with high-speed photography. The experimental results showed the following:(1) high-velocity multiple cavitating jets occurred behind the multi-orifice plates, and the cavitating flow fields were characterized by topological structures;(2) the longitudinal velocity at each cross-section exhibited a sawtooth-like distribution close to the multi-orifice plate, and each sawtooth indicated one jet issuing from one orifice;(3) there were similar magnitudes and forms for the longitudinal and vertical turbulence intensities at the same cross-section;(4) the variation in amplitude of Reynolds stress increased with an increase in orifice number; and(5) the cavitation clouds in the flow fields became denser with the increase in orifice number, and the clouds generated by the staggered layout of orifices were greater in number than those generated by the checkerboard-type one for the same orifice number. The experimental results can be used to analyze the mechanism of killing pathogenic microorganisms through hydrodynamic cavitation.     

地下水源热泵回灌过程颗粒迁移-脱离模型及堵塞区判定

开展多孔介质中悬浮颗粒的迁移-脱离过程研究对地下水回灌工程、注浆工程和石油工程等具有重要意义。以地下水源热泵工程为依托,提出了描述颗粒迁移-脱离过程的波浪状曲面模型,研究不同的粒径组合以及不同压力对多孔介质中颗粒迁移以及脱离特性的影响。在此基础上,采用Comsol对典型地下水源热泵工程进行模拟,揭示了不同粒径及压力分布条件下回灌堵塞区分布规律。结果表明:在相同颗粒粒径组合(相同临界速度)下,压力越大,可以脱离的悬浮颗粒的范围越大;在相同压力下,临界速度越大,可以脱离的悬浮颗粒的范围越小;其他条件相同时,位置离抽水井和回灌水井越近,压力越大,渗流速度越大,悬浮颗粒越容易脱离。     

PERIODICAL PRESSURE-DRIVEN FLOWS IN MICROCHANNEL WITH WALL SLIP VELOCITY AND ELECTRO-VISCOUS EFFECTS

In a microfluidic system, the flow slip velocity on a solid wall can be the same order of magnitude as the average velocity in the microchannel. The flow-electricity interaction in a complex microfluidic system subjected to a joint action of wall slip and electro-viscosity is an important topic. An analytical solution for the periodical pressure-driven flow in a two-dimensional uniform microchannel, with consideration of wall slip and electro-viscous effect is obtained based on the Poisson-Boltzmann equation for the Electric Double Layer (EDL) and the Navier-Stokes equations for the liquid flow. The analytic solutions agree well with the numerical solutions. The analytical results indicate that the periodical flow velocity and the Flow-Induced Electric Field (FIEF) strongly depend on the frequency Reynolds number (Re = ωh²/v), that is a function of the frequency, the channel size and the kinetic viscosity of fluids. For Re<1 the flow velocity and the FIEF behave similarly to those in a steady flow, whereas they decrease rapidly with Re as Re>1. In addition, the electro-viscous effect greatly influences the periodical flow velocity and the FIEF, particularly, when the electrokinetic radius κH is small. Furthermore, the wall slip velocity amplifies the FIEF and enhances the electro-viscous effect on the flow.     

Air flow inside a vertical pipe induced by a free-falling water jet

The air flow induced by a water jet freely falling inside a vertical pipe with its top and bottom both open to the atmosphere was investigated experimentally and numerically. In the experiments, the radial air velocity distribution and the air pressure variation along the vertical pipe were measured. The air drag of the falling water jet was related to the jet surface disturbance and analyzed by introducing the equivalent friction factor. A predictive model was developed for the air flow inside a 3-m-high pipe based on the momentum equation and its results compared well with the experimental measurements. Numerical simulations were also conducted by approximating the free-falling water jet as a continuous moving solid with diameter and velocity varying in the direction of motion. The effects of pipe size on the air velocity profile and the induced air flow rate were examined. The simulation results showed that the streamwise air velocity profiles inside pipes of different sizes approached the same after a certain traveling distance. The maximum induced air flow rate was found at the pipe diameter of about 20 times of initial water jet diameter.     

Wavy properties and analytical modeling of free-surface flows in the development of the multi-domain method

The wavy(oscillatory both in space and in time) properties of free-surface flows due to presence of floating bodies are analyzed within the framework of the potential-flow theory by assuming that the fluid is perfect and flow irrotational. A so-called new multi-domain method has been developed based on the fluid domain division by an analytical control surface surrounding bodies and the application of different methods adapted in the external and internal domains. In the analytical domain external to the control surface, the fundamental solution satisfying the linear boundary condition on the free surface associated with a point singularity(often called Green function and referred here as point solution) is applied to capture all wavy features of free-surface flows extending horizontally to infinity. Unlike classical studies in which the control surface is discretized, the unknown velocity potential and its normal derivatives are expressed by expansions of orthogonal elementary functions. The velocity potential associated with each elementary distribution(elementary solutions) on the control surface can be obtained by performing multi-fold integrals in an analytical way. In the domain internal to the control surface containing the bodies, we could apply different methods like the Rankine source method based on the boundary integral equations for which the elementary solutions obtained in the external domain playing the role of Dirichlet-to-Neumann operator close the problem.