Rapid Flow Startup in Filled Horizontal Pipelines

Maintenance or repair of water mains may require the interruption of flow. Reinitiation of flow may present opportunities for the interaction of air and the accelerating water, resulting in undesirable pressure transients. This study focuses on air intrusion during flow startup in an initially filled horizontal pipeline supplied by a constant-head reservoir. Flow was initiated by opening the downstream end, allowing a free discharge at that point. During the initial phases of flow startup, an air cavity intruded in the upper portion of the pipe cross section while water exited the pipeline through the lower portion. The initial reservoir head controlled the rate of water velocity increase and, thus, the air intrusion advance. Air intrusion occurred until the water velocity was sufficient to arrest the intrusion. Higher reservoir heads resulted in the subsequent expulsion of the intrusion from the pipeline. However, for lower reservoir heads, the intrusion was not expelled, but readvanced to a final position that was controlled by shear forces. Criteria are developed for the flow conditions necessary to arrest the air intrusion in a horizontal pipeline as well as the intrusion lengths to be expected.     

Numerical Simulation Software for Oil Sand Slurry Flow in Flexible Pipelines

In order to optimize the hydraulic transportation system efficiency and cost in the surface extraction of Athabasca oil sand deposits in Canada, there is a desire to extend the hydraulic transport system to production faces in oil sands mines using mobile train of Flex-Rite-based flexible pipelines. Hydraulic transportation system based on flexible-pipe arrangement has been shown to be more competitive than the dump-truck transportation system. This flexible arrangement introduces a unique set of hydraulic transport problems which needs rigorous modeling, experimentation, and analysis to understand the system production capacities and efficiency. Part of the work presented here is an attempt to provide multiphase oil sand slurry simulation and modeling by developing a slurry flow simulator, a graphical user interface-based software, for Flex-Rite flexible-pipe train, a form of hydraulic transportation system. Such software provides a tool/platform for rigorous experimentation and analysis of flow and production capacities.     

低速高混合比水平气力输送临界速度

通过分析水平气力输送系统悬挂式电子称量装置的固体物料输送量记录曲线,判定了输送状态的稳定性.进而提出了中细颗粒(d_s ≤ 0.5mm)、高混合比(μ_s=30~150)、水平低速(u_g<15m/s)输送临界速度的经验关联式。     

Interaction of Particles and Near-Wall Lift in Slurry Pipelines

In pipeline transport of slurries, it is desirable that the solid particles should be suspended by the fluid phase. Within the body of the flow, turbulent diffusion promotes suspension, but this mechanism is not effective near the lower boundary. Under certain conditions, near-wall fluid lift can provide the necessary support for the particles. The Kutta-Zhukovski equation is used to relate the lift force to the shape of the fluid velocity profile. Comparison with experimental findings shows that this lift may be associated with profiles of solid concentration that show a decreased concentration as the bottom of the pipe is approached. Observed reductions of pressure gradients result from this “off-the-wall” lift force. In certain instances, the slurry pressure gradient is found to be less than that for the “equivalent fluid,” with favorable implications for pipeline economics.     

Liquid Metal Flow in Horizontal Rods

The flow velocity and flow pattern of liquid tin contained in a long horizontal boat have been determined by radioactive tracer techniques. The major flow resulted from buoyancy forces generated by an imposed temperature gradient along the melt. The flow pattern in the longitudinal direction was observed to be unicellular. Flow in planes transverse to the longitudinal direction was also observed. A small adverse vertical temperature gradient was detected in the melt and is believed to be the driving force for the transverse flow. The results indicate that the flow velocity increases linearly with the average temperature gradient between the hot and cold ends of the melt, in the temperature range examined. The velocity is reproducible and is not particularly sensitive to slight variations in experimental procedure. The velocity is not dependent on the temperature distribution (linear or nonlinear) along the melt, providing there are no sections of the melt with a zero temperature gradient. In this case, fluid does not flow through these sections. The flow velocity increases with increasing average temperature of the melt. The results are in general agreement with the results predicted by a modification of Batchelor’s solution of fluid flow in a rectangular cavity. L. C. MacAULAY, Formerly a Graduate Student, Department of Metallurgy, University of British Columbia     

气液两相管流流型信号的小波去噪处理

流型信号能够反映气液两相管流的流动特征,它们往往会伴随着各种随机噪声,为此建立了一座气液两相流的综合试验装置,提取气液两相管流的流型信号．采用小波变换对信号样本的进行多尺度分解,利用信号和噪声在不同尺度上的特性把它们区分开来,消除噪声后再对信号进行重构,得到了较好的去噪效果．     

Maximum Velocity and Regularities in Open-Channel Flow

Maximum velocity in a channel section often occurs below the water surface. Its location is linked to the ratio of the mean and maximum velocities, velocity distribution parameter, location of mean velocity, energy and momentum coefficients, and probability density function underpinning a velocity distribution equation derived by applying the probability and entropy concepts. The mean value of the ratio of the mean and maximum velocities at a given channel section is stable and constant, and invariant with time and discharge. Its relationship with the others in turn leads to formation of a network of related constants that represent regularities in open-channel flows and can be used to ease discharge measurements and other tasks in hydraulic engineering. Under the probability concept, the ratio of mean and maximum velocities being constant means that the probability distribution underpinning the velocity distribution and other related variables is resilient, and that the same probability distribution is governing various phenomena observable at a channel section and explains the regularities in open-channel flows.     

Clear-Water Scour below Underwater Pipelines under Steady Flow

Experiments on clear-water scour below underwater pipelines (initially laid on the sediment bed) in uniform and nonuniform sediments under steady flow were conducted. Equilibrium scour profiles were modeled by a cubic polynomial. The experimental results are examined to describe the influence of various parameters on equilibrium scour depth. The equilibrium scour depth ds increases with increase in approach flow depth h for shallow flow depths, becoming independent of higher flow depths when h/b>5, where b=pipe diameter. However, the curves of scour depth versus sediment size d and Froude number Fb have a maximum value of ds/b = 1.65 at b/d = 27 and Fb = 0.6. The influence of sediment gradation on scour depth is prominent for nonuniform sediments, which reduce scour depth to a large extent due to the formation of armor layer within the scour hole. The influence of different shaped cross sections of pipes on the scour depth was investigated, where the shape factors for circular, 45° (diagonal facing) and 90° (side facing) square pipes obtained as 1, 1.29, and 1.91, respectively. Using the data of scour depths at different times, the time variation of scour depth is scaled by an exponential law, where the nondimensional time scale increases sharply with increase in Froude number characterized by the pipe diameter. In addition, clear-water scour below circular pipelines laid on a thinly armored sand bed (the sand bed is overlain by a thin armor layer of gravels) was experimentally studied. Depending on the pipe diameter, armor gravel, and bed-sand sizes, three cases of scour holes were recognized. The comparison of the experimental data reveals that the scour depth below a pipeline with an armor layer under limiting stability of the surface particles (approach flow velocity nearly equaling critical velocity for surface particles) is greater than that without armor layer for the same sand bed, if the secondary armoring formed within the scour hole is scattered. In contrast, the scour depth with an armor layer is less than that without armor layer for the same sand bed, when the scour hole is shielded by the secondary armor layer.     

Critical Flow Section in Collector Channel

This paper shows how the critical flow section in a collector channel can be located by solving the dynamic equation of spatially varied flow, Manning's equation, and making use of the singular-point concept. In addition to channel length and tailwater elevation, the occurrence of a critical flow section in a spatially varied flow also depends on the combination of channel cross-sectional geometry, roughness, slope, and inflow rate. When the critical flow section is necessary to be developed in a collector channel, the two dimensionless parameters (Fq∕S0 representing the design capacity and N∕S0 representing the channel roughness) derived in this study guide selection of channel cross-sectional parameters. A set of design charts is provided for trapezoidal channels with a side slope of 1V:1H, 0.5V:1H, or 0V:1H.     

Sediment Entrainment at High Flow Velocity

In dredging practice sand is eroded at very high flow velocities using water jets. Breaching of dikes or dams is another process where sediments are eroded under the influence of high flow velocities. The existing pick-up functions were developed for relative low values of bed shear stress and hence overestimate erosion. Conventional pick-up functions can be made suitable for dealing with high-velocity erosion by taking the permeability of the sediment into account. This can be achieved by modifying the critical Shields parameter. The procedure is demonstrated using the van Rijn pick-up function. The theory is compared with experiment, and agreement is found to be good.     

Flow and Velocity Distribution in Meandering Compound Channels

An investigation of flow and velocity distribution in meandering compound channels with over bank flow is described. Equations concerning the three-dimensional variation of longitudinal, transverse, and vertical velocity in the main channel and floodplain of compound section in terms of channel parameters are presented. The flow and velocity distributions in meandering compound channels are strongly governed by interaction between flow in the main channel and that in the floodplain. The proposed equations take adequate care of the interaction affect. Results from the formulations, simulating the three-dimensional velocity field in the main channel and in the floodplain of meandering compound channels are compared with their respective experimental channel data obtained from a series of symmetrical and unsymmetrical test channels with smooth and rough sections. The aspect ratio of the test channels varies from two to five. The equations are found to be in good agreement with the experimental data. The formulations are verified against the natural river and other meandering compound channel data. The power laws used for simulating the three-dimensional velocity structure are found to be quite adequate.     

Horizontal Information Flow in Spoken Sentence Production.

In 4 experiments the authors used a variant of the picture-word interference paradigm to investigate whether there is a temporal overlap in the activation of words during sentence production and whether there is a flow of semantic and phonological information between them. Experiments 1 and 2 demonstrate that 2 semantically related nouns produce interference effects either when they are in the same or different phrases of a sentence. Experiments 3 and 4 demonstrate that 2 phonologically related nouns produce facilitation effects but only when they are within the same phrase of a sentence. The results argue against strictly serial models of multiple-word access and provide evidence of a flow of semantic and phonological information between words during sentence production. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Velocity Profile and Flow Resistance Models for Developing Chute Flow

A developing boundary layer starts at the spillway crest until it reaches the free surface at the so-called inception point, where the natural air entrainment is initiated. A detailed reanalysis of the turbulent velocity profiles on steep chutes is made herein, including mean values for the parameters of the complete turbulent velocity profile in the turbulent rough flow regime, given by the log-wake law. Accounting both for the laws of the wall and the wake, a new rational approach is proposed for a power-law velocity profile within the boundary layer of turbulent rough chute flow. This novel approach directly includes the power-law parameters and does not require for a profile matching, as is currently required. The results obtained for the turbulent velocity profiles were applied to analytically determine the resistance characteristics for chute flows. The results apply to the developing flow zone upstream of air inception in chute spillways.     

充填料浆流动温变性研究

为解决矿山充填料浆堵管事故频发的问题,以具有代表性的不同配比充填料浆为研究对象,通过安东帕MCR102高级流变仪获取并分析相关数据,重点研究了充填料浆的温度对高浓度充填料浆流变特性的影响,探索温度变化对充填料浆流动性能的影响.研究结果表明:(1)高浓度全尾砂充填料浆的流变性能会随着料浆的温度变化而发生变化;(2)随着温...     

Uniform and Critical Flow Computations

The application of theory developed for direct integration of gradually varied flow equations to uniform and critical flow computation greatly reduces the computational effort. A small generalized subroutine is able to compute accurately the various parameters involved in the computation for all types of natural and constructed cross sections. Although the equations are implicit, in a majority of cases the number of iterations needed to achieve the required accuracy is less than 3. The method is even useful for computation by hand held calculators.     

Critical Depth Relationships in Developing Open-Channel Flow

Doubts have been expressed about the validity of the critical depth defined in terms of the minimum specific energy head of the free-surface streamline when dealing with developing open-channel flows. This note examines the two approaches for defining critical flow, that based on the minimum specific energy of the free-surface streamline and that based on the mean energy head of the whole flow section. Large differences for the dimensionless critical depths are obtained with the two methods due to each critical depth proving to be a different control point on the free-surface profile. It is argued that both methods are different alternatives, although the critical depth concept was different in each case. Theoretical support to critical flow computations based on the free streamline is provided. An alternative approach for computing the discharge characteristics of broad-crested weirs based on the energy loss inside the boundary layer is also proposed.     

Deflecting Velocity Rod for Flow Measurements in Small Channels

A hinged rod, when immersed in flowing water, deflects against its weight due to the hydrodynamic force of water. A relationship was derived to calculate the average flow velocity in small channels from the deflection of the rod, length and thickness of the rod, density of the rod's material, flow depth, and an experimentally determined rod's velocity coefficient. The rod's velocity coefficient was found to be invariant with flow velocity (V) and Reynolds number (R) for the range investigated in this study (V ? 60 cm∕s and 25,000 ? R ? 60,000). The calculated velocity compared very well with the measured velocity, with an average error of only 0.7%. Analysis suggested that a rectangular rod made of seasoned wood (density ? 0.7) with length = 100 cm, width = 2 to 4 cm, and thickness = 3 to 5 cm will provide a simple but acceptable technique for determination of average flow velocity in small prismatic channels having a flow velocity ?1 m∕s and flow depth ?45 cm with less than 5% error.     

Velocity Distributions in Spatially Varied Flow with Increasing Discharge

The experimental study presented in this paper explores the distribution of the mean velocities for a channel receiving spatially varied (SV) inflow from directly above the centerline of the channel via sets of nozzles. The velocity components u, v, and w have been measured using a laser Doppler velocimeter. Initially the validity of the law of the wall in the channel receiving SV inflow was investigated. It was found that the measured velocity profile within the inertial sublayer region near the channel bed falls below the line representing the log law. Further, if the SV inflow enters at the center of the channel, the degree that the data depart from the log law increases from the sidewall toward the center of the channel. The structures of the velocity distributions are also presented in detail. The results include both near field, that is the area close to where the flow enters the channel, and far field measurements. It was found that the influence of the SV inflow on velocity profiles is largely contained within the SV inflow zone and that the influence within this zone reduces in the downstream direction. At any one section within this zone the influence reduces from the center of the channel toward the sidewall. In addition, some features of the secondary flow established by the SV inflow are described.