连续弯道水流紊动特性试验研究

采用电磁流速仪, 在接近天然河道形态的连续弯道中, 对沿程断面上各点的脉动流速进行量测.根据测得的数据分析得到了紊动能谱、紊动强 度、紊动切应力、紊动能、紊动参数等的全断面分布.研究结果表明水流紊动主要集中在10 Hz以下,不同环流形式与各种紊动量之间会互相影响,边壁处纵向紊动强烈、横向和垂向紊动较弱.     

定床弯道内水沙两相运动的数值模拟

在适体同位网格中采用非正交曲线坐标系下的三维k-ε-kp固液两相双流体湍流模型研究弯道内水流和悬浮泥沙运动,主要计算了试验室S型水槽内清水流动的三维流场、120°弯道内水沙两相流动中底沙与底流的运动轨迹以及S型水槽内水沙两相流动的两相流场和泥沙浓度场. 对于S型水槽内清水流动,数值结果与试验结果吻合良好. 120°弯道内水沙两相流动中固液两相的运动轨迹在弯道直线段基本重合,在弯道内泥沙轨迹逐步偏离水体轨迹,其偏离程度随泥沙粒径增大而增大. 从S型水槽内水沙两相流动计算结果中发现泥沙纵向流速在壁面附近比水流纵向速度大,在远离壁面区域比水流纵向速度小;弯道内泥沙横向流速比水流横向流速小;垂向流速在直线段和泥沙沉速相当,在弯道内受螺旋水流影响而变化;两相流速差别随泥沙粒径增大而变大;泥沙浓度呈现下浓上稀的分布,在弯道内横向断面上呈现凸岸大凹岸小的分布,泥沙浓度随泥沙粒径增大而减小.      

矩形平底渠道淹没水跃区的水头损失

研究了矩形平底明渠淹没水跃区的水头损失。根据Rajaratnam对淹没水跃区的流速分布、壁面切应力、最大流速的试验成果和Verhoff附壁射流区断面流速分布的计算公式,应用紊流边界层理论研究了淹没水跃区的边界层发展和沿程水头损失的计算方法。根据动量方程和能量方程研究了淹没水跃区的跃前断面水深、总水头损失、局部水头损失、消能率的计算方法。给出了淹没水跃区最大流速、紊流边界层厚度、沿程水头损失、总水头损失、局部水头损失、局部阻力系数、消能率的计算方法。研究表明:淹没水跃区的总水头损失是跃前断面弗劳德数、跃前水深和淹没度的函数,沿程水头损失和局部水头损失与跃前断面流速、水深、水跃长度、跃前断面的特征雷诺数和消力池宽度有关。淹没水跃区的水头损失主要是局部水头损失,消能率随着弗劳德数的增加而增加。     

透水床面明渠湍流时空平均特征的大涡模拟与分析

基于大涡模拟数据,研究了理想粗糙透水床面明渠湍流的时空平均特性. 考虑到空间异构性,对比分析了不同位置的时空平均流速、雷诺剪应力、构造剪应力、脉动幅度的垂线分布. 结果表明:第一,顶层床面之上,空间异构性的影响较小,不同位置的双平均流速符合类似的对数分布,但由于透水床面影响,卡门常数较不透水床面小;在床面附近,空间异构性影响较大,不同位置的双平均流速分别符合线性分布与多项式分布;在透水河床内部,靠近底层球孔的双平均流速为上部球孔双平均流速的1.55 倍. 第二,床面之上,雷诺剪应力占总剪应力的95% 以上,占有主体地位;床面附近,紊动较大,构造剪应力不能忽略,其值大约占总剪应力的15%.由于流场的各向异性,纵向与垂向的脉动幅度有所差异.      

90°弯道明渠横向环流的大涡模拟研究

采用气液两相流大涡模型模拟90°弯道明渠水流的水力特性。使用有限体积法对控制方程进行离散;使用压力隐式算子分裂PISO(Pressure-Implicit with Splitting of Operators)算法求解速度与压力的耦合;采用了VOF(Volume of Fluid)法模拟自由水面。通过计算得到弯道处流速、压强系数、横向环流强度等水力参数的分布规律。分别比较弯道纵向流速与横向流速的模拟值与实验值,二者吻合较好。通过分析弯道环流的流态特征得出:因受重力作用与水流在流经弯道时发生的离心现象的影响,凸岸附近较凹岸存在较大的二次流强度的结果;凸岸与凹岸压强系数均沿程增大,当达到弯顶时,水面横比降达到最大值;弯道横向环流强度随弯道角度增大而逐渐增大,其最大值出现在明渠底部。     

自由水跃区壁面阻力的研究

根据已有文献对附壁射流区流速分布和壁面阻力的试验成果,分析了自由水跃区断面流速分布和最大流速沿程分布规律;首次根据边界层的动量积分方程分析了水跃主体段的射流厚度、水跃区的壁面切应力系数、壁面阻力系数的变化规律;给出了边界层厚度、壁面局部阻力系数、壁面阻力系数、平均壁面阻力系数的计算方法,并将计算结果与已有文献的试验资料进行了比较。结果表明:由本文式(9)和式(26)得到的数据与文献中的试验数据吻合较好;在Fr1≥5.45时,式(29)的计算结果与试验较吻合,在Fr1?5.45时,其计算结果与试验偏差较大;采用本文公式(34)计算水跃的共轭水深,与文献所得结果的最大误差为3.643%。     

弯道水流数值模拟研究

采用边界拟合坐标技术,生成边界处正交的曲线网格,在曲线坐标系中进行弯道水流数值计算。借鉴现有关于弯道水流流速分布的研究成果,对曲线坐标系平面二维浅水方程作了修正,修正后的方程组能够计入弯道环流引起的横向的动量交换,即考虑了二次流对流线弯曲的复杂水力特性的影响。通过连续弯道实例计算,验证了该模型的可靠性和实用性。     

曲线坐标系下平面二维浅水模型的修正与应用

借鉴有关弯道水流流速分布的研究成果,计入弯道环流引起的横向的动量交换,对曲线坐标系平面二维浅水方程做了修正;采用边界处正交的曲线网格生成技术,处理复杂的计算区域边界。采用修正后的模型对90°弯道水流进行了数值模拟,并与原模型的计算结果及实测资料进行了比较,结果表明该模型能够有效地模拟流线弯曲的复杂水流的水力特性。     

多焊点情况下胶焊单搭接头的静力分析

以胶接分析为基础,将焊点视为大剪切弹性模量胶粘荆,假设被粘体切应力沿厚度线性分布,胶层和焊点切应力沿厚度方向不变,建立了多焊点情况下胶焊单搭拉剪接头的线弹性应力解析模型.计算结果表明:被粘体正应力和胶层切应力解析解与有限元模型吻合得较好.对焊距的参数研究表明:胶焊单搭拉剪接头连接区纵向正应力和切应力随焊距减少而分布更均匀,峰值切应力下降,与前人的试验结果一致.     

浅水波方程的高精度隐式WCNS格式

设计了高精度隐式WCNS格式,用于数值求解浅水波方程。方程通量导数采用四阶隐式紧致差分格式计算;半节点通量采用五阶非线性加权插值方法计算。对于含源项浅水波方程,采用特殊的源项处理,使得隐式WCNS格式具有和谐性,即在静水条件下保持流速为零,水位为常数。通过线性算例及几个经典的无源项和含源项数值算例对WCNS格式进行测试,结果表明:该格式在光滑区具有四阶精度,在间断处具有良好的捕捉激波能力,同时对于含源项问题具有保持静水条件下定常解的和谐性。     

植被作用下的复式河槽流速分布特性

通过水槽试验，探讨了不同滩地植物 (乔木、灌木和野草) 对复式河槽流速分布的影响. 详细地介绍试验过程及三维流速仪ADV的测量原理. 试验时， 选塑料吸管、鸭毛和塑料大草分别模拟乔木、灌木和野草. 同时，考虑了流量、床面底坡对 流速分布的影响. 试验结果表明，滩地未种树的复式河槽在大的相对水深时，流速满足对数 分布；滩地种树后，主槽流速增大，流速分布复杂，滩地流速减小，呈 S 形分布，不同植物的S 形分布是不同的. 这种S 型分布将水流划分为3个区的复杂行为，每区的范围与水深，垂线位置和植物类型有关. 床面坡度对流速分布的影响非常明显     

Hydrodynamics of viscous fluid through porous slit with linear absorption

The exact solutions for the viscous fluid through a porous slit with linear ab-sorption are obtained. The Stokes equation with non-homogeneous boundary conditions is solved to get the expressions for the velocity components, pressure distribution, wall shear stress, fractional absorption, and leakage flux. The volume flow rate and mean flow rate are found to be useful in obtaining a convenient form of the longitudinal velocity component and pressure difference. The points of the maximum velocity components for a fixed axial distance are identified. The value of the linear absorption parameter is ran-domly chosen, and the rest available data of the rat kidney to the tabulate pressure drop and fractional absorption are incorporated. The effects of the linear absorption, uniform absorption, and flow rate parameters on the flow properties are discussed by graphs. It is found that forward flow occurs only if the volume flux per unit width is greater than the absorption velocity throughout the length of the slit, otherwise back flow may occur. The leakage flux increases with the increase in the linear absorption parameter. Streamlines are drawn to help the analysis of the flow behaviors during the absorption of the fluid flow through the renal tubule and purification of blood through an artificial kidney.     

基于五阶WENO格式的燃气在药床中流动过程二维两相流研究

为研究内弹道初始阶段中心点火管燃气在膛内药床中的流动特性和传播规律,设计了可视化点传火实验平台,并进行了膛内假药床的点传火实验。基于加权本质无震荡(weighted essentially non-oscillatory, WENO)格式,构造了膛内轴对称二维内弹道两相流模型,对膛内燃气在假药床中的流动过程进行数值模拟。计算结果与可视化实验结果符合较好,全局压力平均误差为5.35%。表明数值计算准确地描述了燃气流动特性,完整地呈现了点火管燃气在假药床中的发展过程。在点火初始阶段,膛内压力径向效应明显,气相沿径向传播较快,药床药粒基本不会发生运动;随着燃气逐渐在膛内传播,膛内压力呈现径向一致、轴向梯度分布的特征,在压力梯度作用下,气相轴向速度开始占据主导,径向速度在膛底和中部区域减小为零,而固相速度随气相速度变化而变化;气相在到达弹底前,由于固相颗粒的壅塞,会提前出现速度反向波动现象。     

An insitu borescopic quantitative imaging profiler for the measurement of high concentration sediment velocity

The design, calibration, and testing of a borescopic quantitative imaging profiler (BQuIP) system, suitable for the insitu measurement of two components of the instantaneous velocity in high sediment concentration flows, are presented. Unlike planar quantitative imaging techniques, BQuIP has a concentration-dependent field of view, requiring detailed calibration. BQuIP is demonstrated in unidirectional sheet flow in an open channel flume with a narrow-graded sand with median diameter 0.25 mm. Acoustic velocity measurements are made in the suspension region above the BQuIP measured region yielding a continuous measurement of velocity and turbulent stress from the immobile bed to just below the free surface. The temporal history at a point reveals the sheet flow sediment velocities to be highly intermittent, and the spectra reveal a broad range of temporal scales close to −5/3 in slope for the streamwise velocity component. At its core BQuIP is a quantitative imaging technique giving it significant flexibility in terms of both the spatial and temporal analysis parameters (e.g., interrogation subwindow size and Δt, the time between images in a pair to be analyzed), allowing it to have tremendous dynamic range in terms of the velocities that can be measured.     

Flow Field Around Single and Tandem Piers

The present study provides a comparison between the flow pattern around two circular piers in tandem and a single pier set up on a moderately rough flat bed in a laboratory flume. Velocities are measured by an Acoustic Doppler Velocimeter (ADV). The contours of the time-averaged velocity components, Reynolds shear stresses, turbulence intensities and turbulence kinetic energy at different planes are presented. Streamlines and vectors are used to study the flow features. The analysis of power spectra around the piers is also presented. The results show that the presence of downstream pier changes the flow structure to a great extent, particularly in the near-wake region. Within the gap between the two piers, a stronger and substantial upflow is shaped. However, a weaker transverse-deflection is formed in comparison with that in the single pier. Near the bed, the velocity of flow approaching the downstream pier decreases to 0.2–0.3 times of the approach mean velocity (U ₀) due to the sheltering effect of the upstream pier. In the wake of downstream pier, the flow structure is completely different from the one in the wake of single pier. In comparison with the single pier, the values of turbulence kinetic energy and turbulence intensities show a considerable decrease around the tandem piers. In tandem piers, the high values of turbulence characteristics are found near the downstream pier. There is a recirculation zones just upstream of the sheltered pier close to the bed and another behind that pier near the free surface. The results show a decrease in the strength of vortical structure in the wake of tandem piers in comparison with single pier. It is shown that the formation of flow with different Reynolds number along the flow depth due to the effect of bed roughness, as well as pier spacing, can influence the type of flow regime of tandem case. In addition to enhancing the flow structure indulgence, the present detailed measurements can also be used for verification of numerical models.     

Measuring void fraction and velocity fields of a stepped spillway for skimming flow using non-intrusive methods

Stepped spillways have higher energy dissipation than smoother hydraulic structures used to divert flood discharges. The inception point related to air entrainment is, however, located further upstream causing an undesired bulking of the flow depth. For large discharge rates and for straight stepped spillways, the skimming flow regime may be assumed two dimensional; this is an attractive feature for the application of non-intrusive flow visualization techniques because these methods measure the flow characteristics in the vicinity of the sidewalls which are likely to correlate with the flow at the centre of the flume. This paper tests the hypothesis that such techniques can be used to measure the flow inside the flume. The hypothesis is tested against measurements taken with an intrusive probe. Void fraction contour lines and velocity fields are obtained in 12 different stepped spillway configurations using the image processing procedure and the bubble image velocimetry, respectively. The void fraction and velocity results are overall consistent with the probe measurements. The velocity fields show a persistent underestimation of the probe measurements which can at least be partially explained by sidewall effects and possible probe’s overestimation.     

Monitoring the inception of sediment transport by image processing techniques

 In this paper we present a non intrusive device to detect the inception of sediment transport and to measure bed load in low-submergence flows. A solid state linear CCD camera provides linear images of the sediment movements across a control section, located on the bottom of a laboratory flume. These arrays of information are reassembled to provide a raster image of the bottom of the flume in correspondence of the control section. An on-line operating image processing software counts the number of grains and evaluates their velocity. Received: 25 July 1996/Accepted: 3 February 1997