Motion and deformation of immiscible droplet in plane Poiseuille flow at low Reynolds number

Droplet migration in plane Poiseuille flow is numerically investigated with a dissipative particle dynamics method.The single droplet deformation in the channel flow is first studied to verify the current method and the physical model.The effect of the viscosity ratio between the droplet and the solvent and the effect of the confinement are systematically investigated.The droplet is in an off-centerline equilibrium position with a specific selection of the parameters.A large viscosity ratio makes the droplet locate in a near-wall equilibrium position,and a large capillary number makes the droplet migrate to the near-centerline region of the channel.For the droplet migration at the same Capillary number,there is a critical width of the channel,which is less than twice of the droplet diameter,and the droplet will only migrate to the channel centerline if the width is less than this critical value.     

COUPLING DISTINCT AND CONTINUOUS MEDIUM MODEL FOR FLOW ANALYSIS IN A FRACTURED ROCK MASS AND ITS APPLICATION

Fractures in a rock mass can be divided into dominant fracture system and network fracture system. An approach for the analysis of three dimensional ground water flow in a fractured rock mass is presented, in which flow in the dominant fracture system is described by a distinct medium model while flow in the network fracture system plus rock matrices (if considered) is described by a continuous medium model, and the two models are coupled by hydraulic head and flux. The coupling model facilitates to calculate one-by-one the fluid flow in the dominant fractures which are functioned as the major water transmission conduits, and it avoids unnecessary calculating fluid flow in individual network fractures which are numerous in number. In this way, the method can be applied to a large-sized calculation domain. In addition, a method of using network geometry data to calculate its equivalent porous permeability is presented in the paper, and the model implementation of water source and sink such as the pumping     

3-D simulation of transient flow patterns in a corridor-shaped air-cushion surge chamber based on computational fluid dynamics

The 3-D characteristics of the water-air flow patterns in a corridor-shaped air-cushion surge chamber during hydraulic transients need to be considered in the shape optimization. To verify the reliability of the water-air two-phase model, namely, the volume of fluid model, the process of charging water into a closed air chamber is successfully simulated. Using the model, the 3-D flow characteristics under the load rejection and acceptance conditions within the air-cushion surge chamber of a specific hydropower station are studied. The free surface waves, the flow patterns, and the pressure changes during the surge wave process are analyzed in detail. The longitudinal flow of water in the long corridor-shaped surge chamber is similar to the open channel flow with respect to the wave propagation, reflection and superposition characteristics. The lumped parameters of the 3-D numerical simulation agree with the results of a 1-D calculation of hydraulic transients in the whole water conveying system, which validates the 3-D method. The 3-D flow structures obtained can be applied to the shape optimization of the chamber.     

Estimation of discharge and its distribution in compound channels简

Results of research into a compound channel having width ratio(?)in excess of 11 are presented in the form of boundary shear distributions across the compound cross section.New relationship is derived between the percentage of shear carried by the flood plains(%)fp S and the percentage of area occupied by the flood plains(%)fp A.The equation so derived is taken as the basis to develop a new methodology to predict the stage discharge relationship specifically for wide compound channels using Darcy’s friction factor(f)for the main channel and flood plain regions.The methodology also is used for compound channels with smaller width ratios by applying the appropriate relation for%fp S derived earlier by different researchers and seems to work well.Next,as a corollary to the methodology,separate formulae are proposed to estimate flow distribution in main channel and flood plain regions.The proposed method and its corollary are tested for their validity against well-published small-scale data series of previous researchers along with some large-scale data series from EPSRC-FCF(A-Series)compound channel experiments and very good agreement is observed between the measured values and predicted values for total flow as well as zonal distribution of flow.The methodology is also applied to some compound river section data published in literature and is found to serve well the purpose of predicting flow in real world application.This new method gives the least RMS value of error for discharge prediction compared with some other well-known methods used for estimating stage-discharge relation in compound channels by considering all data sets.     

Large-eddy simulation of suspended sediment transport in turbulent channel flow

The numerical simulation of the non-cohesive sediment transport in a turbulent channel flow with a high concentration is a challenging but practical task. A modified coherent dynamic eddy model of the Large Eddy Simulation (LES) with a pick-up function is used in the present study to simulate the sediment erosion and the deposition in a turbulent channel flow. The rough wall model is used instead of the LES with the near-wall resolution to obtain the reasonable turbulent flow characteristics while avoiding the high costs in the computation. Good results are obtained, and are used to analyze the sediment transport properties. The results show that the streamwise vortices play an important role in the riverbed erosion and the sediment pick-up, which may serve as guidelines for the sediment management and the water environment protection engineering.     

MECHANISM FOR VISCOELASTIC POLYMER SOLUTION PERCOLATING THROUGH POROUS MEDIA

The pore throat of porous media is modeled as a constricted channel or expanded channel. The flow of viscoelastic polymer solution in pore throat model is studied by numerical method. Relationship between pressure drop and flow rate is developed,viscoelasticity and throat size are found to be two main factors in high flow resistance. According to pore throat model,2-D stochastic channel bundle is put forward to model porous media,which is composed of pore throat models in series -parallel connection with size and length accord to Haring -Greenkorn stochastic distribution. Percolation model of viscoelastic fluid is developed on the basis of Darcy equation and pressure drop vs. flow rate relation in 2-D stochastic channel bundle. Results indicate that the seepage ability of viscoelastic polymer solution decreases with the increase of viscoelasticity,injection rate,and heterogeneity as well as the decrease of mean pore size of porous media. The high pressure drop of viscoelastic fluid at the connection of pore to throat plays a great role in its anomalous high flow resistance through porous media.     

Simulation and analysis of ice processes in an artificial open channel

The Middle Route Project for South-to-North Water Transfer, which consists of a long artificial open channel and various hydraulic constructions, is a big water conveyance system. A numerical modeling of water conveyance in the ice period for such large-scale and long distance water transfer project is developed based on the integration of a river ice model and an unsteady flow model with complex inner boundaries. A simplified method to obtain the same flow discharge in the upstream and downstream of the structure by neglecting the storage effect is proposed for dealing with the inner boundaries. According to the measured and design data in winter-spring period, the whole ice process, which includes the formation of the ice cover, its development, the melting and the breaking up as well as the ice-water dynamic response during the gate operation for the middle route, is simulated. The ice characteristics and the water conveyance capacity are both analyzed and thus the hydraulic control conditions for a safety regulation are obtained. At last, the uncertainties of some parameters related to the ice model are discussed.     

A coupled 1-D and 2-D channel network mathematical model used for flow calculations in the middle reaches of the yangtze river

A coupled one-dimensional (1-D) and two-dimensional (2-D) channel network mathematical model is proposed for flow calculations at nodes in a channel network system in this article.For the 1-D model, the finite difference method is used to discretize the Saint-Venant equations in all channels of a looped network.The Alternating Direction Implicit (ADI) method is adopted for the 2-D model at the nodes.In the coupled model, the 1-D model provides a good approximation with small computational effort, while the 2-D model is applied for complex topography to achieve a high accuracy.An Artificial Neural Network (ANN) method is used for the data exchange and the connectivity between the 1-D and 2-D models.The coupled model is applied to the Jingjiang-Dongting Lake region, to simulate the tremendous looped channel network system, and the results are compared with field data.The good agreement shows that the coupled hydraulic model is more effective than the conventional 1-D model.     

An Investigation of Turbulent Rectangular Jet Discharged Into A Narrow Channel Weak Crossflow

A computational investigation of the mean flow field of turbulent rectangular jets issuing into a narrow channel crossflow is presented. The length of the jet slot spans more than 55% of the crossflow channel bed, leaving a small clearance between the jet edge and sidewalls. A finite volume code employing the standard k-εmodel is used to predict the mean, three-dimensional flow field. The mean flow field is investigated for two velocity ratios （6 and 9）. Important flow features, such as the formation of different vortical structures and their characteristics owing to different values of the velocity ratio, are discussed. Some predicted results are compared with the experimental data reported in the literature. The predicted mean and turbulent flow properties are shown to be in good agreement with the experimental data.     

《南水北调与水利科技》优先数字出版声明

The turbulent flows through the channels with abrupt cross-sectional changes are common and importantphysical process in nature.For a better prediction of the mean flow and turbulent characteristics for this problem,atwo-dimensional depth-averaged numerical model is developed.The model is robust and accurate in reproducing therecirculation flow behind a groyne and turbulent flows in channels with abrupt cross-sectional changes,when com-pared to the available experimental data of mean velocities and turbulence kinetic energy.Our results reveal that theabrupt cross-sectional change of a channel can affect the flow pattern significantly and introduces the complex turbu-lence characteristics.In particular,when the channel has an abrupt expansion,the mean flow pattern is mainly in lon-gitudinal direction with rather small transverse component.Meanwhile,a recirculating region forms behind the expan-sion position and the turbulence has very strong intensity within this region.For the flow in the channel with an ab-rupt contraction,the longitudinal component of the flow is decreased by the obstruction on one side and accelerated onthe other side,whereas the transverse velocity is small.The turbulence is extraordinarily strong in the regions adja-cent to the contraction wall in the narrow channel.In both cases of abrupt cross-sectional changes,the TKE is genera-ted dominantly by the shear of the longitudinal velocities.     

Application of Genetic Programming in Stage Hydrograph Routing of Open Channels

Routing is a technique used to simulate and predict changes in water flow along a river or channel. There are several hydraulic flow routing methods that model channel flow with high accuracy using lots of data related to channel geometry and specifications, thus making calculations very expensive. In contrast, hydrologic methods are techniques that simplify the calculation of flow conditions in a channel reach. In this paper, a stage hydrograph is modeled in simple and compound channels by genetic programming (GP) as a hydrologic method that does not depend on channel geometry and specifications, channel shape, and modeling time step. Routed hydrographs for simple and compound channels are then compared with a river analysis system model (HEC-RAS) and a coupled characteristic-dissipative-Galerkin procedure in one-dimension (CCDG-1D) as the hydraulic methods, respectively. Results show that the sum of squared differences (SSD) between a stage hydrograph by GP and modeled hydrographs by HEC-RAS and CCDG-1D methods, respectively, are not considerable in simple and compound channels. Moreover, GP is a capable tool to route an acceptable stage hydrograph even by using less geometry specification and time intervals in the detected stage. Those results indicate that the proposed GP method is effective in routing a stage hydrograph.     

复式断面河槽流速横向分布及其对滩唇形成的影响

通过对水流微小控制体进行受力分析，建立了复式断面流速横向分布模型，该模型考虑了侧向副流惯性力的影响。采用实验资料对该模型进行检验，模型计算值与实测值符合较好。运用该模型计算了不同条件下复式断面流速和挟沙力的横向分布，并定量分析了横向分布特性对滩唇形成的影响。分析表明，水流漫滩时，复式断面的横向挟沙力变幅较大，尤其是在主槽和河漫滩交界处，挟沙力减小迅速，而含沙量减小相对较小，泥沙发生淤积，容易形成滩唇。单从水流挟沙力角度考虑，水流漫滩后水深越小、滩槽的糙率差越大，越容易形成滩唇。     

基于个体模型模拟的鱼类对上游水库运行的生态响应分析

建立了一维全河流和二维局部河段的水环境模型，并与基于个体的鱼类模型耦合，从鱼类种群动态角度研究水库运行对下游河流水生态系统的作用。文中选取了漓江下游的一段复式河道，以优势种草鱼和鲫鱼为研究对象，模拟了自然条件和水库调节作用下河道的水环境条件，以及相应的鱼类生长和分布的变化。通过模拟结果的对比分析，发现如果仅考虑水库运行造成的下游水流变化的作用，枯水期水库向河道补水对草鱼有一定的正面影响，对鲫鱼有轻微的负面影响；而在4—5月，水库运行对两种鱼类都存在比较明显的负面影响。本文建立的模型方法可为河流优化管理及水库生态友好运行提供支持。     

复式渠槽水沙输移特性研究综述

水流运动特性受边界的影响较大,由于复式渠槽特有的几何特征和边界条件,当发生漫滩流时,水流结构比较复杂,水流特性和泥沙输移规律均不同于单一渠槽。分别对顺直和弯曲复式渠槽漫滩情况下的流速分布、剪切力分布、水流阻力及泥沙输移特性进行归纳和分析。从复式断面形态、滩槽交互区动量交换、推移质泥沙运动特性以及自然因素条件对水沙输移特性的影响4个方面,对复式渠槽水沙输移特性的研究趋势进行了展望。     

滩地加宽及主槽变化对复式断面过流能力的影响

为了分析不同断面形态对复式断面过流能力的影响,针对概化的复式断面顺直型河道,应用数学模型分别计算并分析了滩地加宽和主槽位置变化河道滩槽流量分配比、沿程水位、河道水力坡降的影响。结果表明：当滩地过水面积小于4~6倍的主槽过水面积时,增大滩地的宽度可以明显降低河道的沿程水位;改变主槽的位置几乎不会影响河道的过流能力。     

矩形明渠三维紊流的数值模拟

在明渠三维流动中，紊流产生的二次流起关键作用，它对主流流场分布，壁面应力及污染物的扩散有很大影响，有时还影响床面的稳定，Ｋ－ε紊流模型及类似的双方程模型不能计算这种二次流动。本文将非线性Ｋ－ε紊流模型用于明渠三维紊流的计算，模型用张量形式推出，比代数应力模型更易推广到复杂边界流动，应用这一模型及另两种代数应力模型对矩形明渠流动进行计算，所得结果，尤其是表述紊流特征的量，与实测资料进行了详细比较，并     

复式断面交汇水流滩槽交界水流特性试验研究

通过在室内自制水槽模型内布置网格,利用先进的声波多普勒流速仪（ADV）测取网格内各点流速。再把各点的流速数据输入软件,通过做切片云图和分析流速数据的方法,研究复式交汇河道滩槽交界水流流态及某一特征断面的剪应力分布。结果表明：滩槽交界附近存在一个流速间断面,在这个区域水流所受阻力较大;复式河道断面的平均流速与剪切应力呈线性关系。     

有植被的河道水流紊动特性模型试验研究

通过物理模型试验,研究了有植被的河道水流紊动特性.试验结果表明,在复式断面河道滩地种植柔性植被后,滩地糙率增大,水流紊动更为剧烈,河道水流紊动强度峰值由原先的滩槽交界区转移到滩地区.滩地的水流紊动强度沿程递减;滩槽交界区的水流紊动强度沿程不断增大;主槽的水流紊动强度主要与床面糙率有关,滩地植被影响了滩地水流的归槽时间,使主槽水流流速沿程增大.     

Analysis of One-Dimensional Modelling for Flood Routing in Compound Channels

In this paper a number of hydraulic aspects concerning the flood routing in compound channels are discussed. In particular, attention is firstly focused on the management of boundary conditions for compound channel flow when 1D modelling is used. In this context, the characteristics theory was used to obtain the complete expression of the eigenvalues of the system and the consequences of the simplification associated to the commonly-used approximation were highlighted. The analysis has shown that the number of physical conditions to be imposed at the boundaries is influenced not only by the Boussinesq coefficient but also by its derivative over the water level. The second part of the paper is devoted to the analysis of unsteady flow simulations. Attention was focused on the role played by the lateral momentum transfer, between main channel and floodplains, within the 1D flood propagation model. In particular, the simulations showed that significant differences may occur between the traditional approach and the methods able to take into account the momentum transfer mechanisms.     

长沟泵站泵装置流道优化与选型研究

经对南水北调长沟泵站肘型和钟型进水流道分别与平直管式、低驼峰式、虹吸式出水流道组合成10个装置流道方案,进行水力优化设计和CFD计算分析,优选出较佳的2种进水-出水流道与优选的2个转轮模型,再组合成4组泵装置,进行装置模型同台对比试验。试验所得最优泵装置即TJ04-ZL-06模型转轮配肘型进水流道-低驼峰出水流道,在设计工况（对应泵站平均扬程3.66、流量33.5m3/s）时装置效率达78.2%,综合性能达到了较理想的目标,大大提高了装置效率和叶轮中心安装高程,不仅减少了工程投资还节约了年运行费。