Movement Properties of Pipe Flow Along Granite Slope of Three Gorges Area of Yangtze River in China

It is well known that, in most cases, soil water doesn't move in the form of laminar flow as described by Darcy law. Only when Reynolds number ( Re ) is no more than 10, does water movement follow Darcy law. A soil profile with 2 9 m long and 2 13 2 60 m deep was excavated on a lower slope located at Zigui County, Hubei Province, China. Field observation found that soil pipes were mainly distributed in the transient layer between horizon B with higher degree of granite weathering and horizon C with lower degree of granite weathering. At the foot of the slope, about 5 7 soil pipes per meter were observed along the vertical direction of the slope. The observed results, obtained by continuous observation of soil pipes and pipe flow processes at granite slope for many rainfall events, indicate that the relationship between velocity of pipe flow and hydraulic gradient along the pipe is parabolic rather than linear. Based on the investigated data of soil, landform, and land use etc., combined with observed data of pipe flow derived from many rainfall events, a pipe flow model was developed. For velocity V p, discharge Q p of pipe flow and radius r of soil pipe, great similarity was found between simulated and observed values. Particularly, the simulated length of soil pipes reflects the great difference among soil pipes as a result of its different position in the soil profile. The length values of 4 soil pipes were estimated to be 98 1%, 27 6%, 11 0% and 3 0% of the longest distance of the catchment, respectively. As a special case of water movement, soil pipe flow follows Darcy Weisbach law. Discharge of pipe flow is much greater than infiltration discharge in common. Only when the depth of groundwater is more than the diameter of soil pipe and water layer submerges soil pipes during rainfall, may pipe flow occur. Under these circumstances, discharge of pipe flow is directly proportional to the depth of groundwater.

Analyses and Modeling of Laminar Flow in Pipes Using Numerical Approach

This paper investigate some important works done on numerical analysis and modeling of laminar flow in pipes. This review is focused on some methods of approach and the analytical tools used in analyzing of the important parameters to be considered in laminar flow;such as frictional losses, heat transfer etc. in laminar flow in pipes of different shapes, and the importance of laminar flow in its areas of applications. Prominent researchers have approached this from different perspectives. Some carried out analysis on the pressure drop as a function of permeability, some worked on friction factor analysis, some discussed heat transfer effects of laminar flow in the entrance region, while some discussed its applications in various industries. Some of these works were done considering a given form of pipe configuration or shape which is circular pipes. Only a few, of the literature reviewed have related their considerations to different forms of pipes. Most consider pipes to be majorly circular in shape, but in industries today some circular pipes have become elliptical in shape due to long time usage of the pipes, which would have contributed to increase in some different forms of losses in the industries. In engineering, efficiency and effectiveness improvement is the major goal, if a research work has been done, considering the important parameters in laminar flow showing their effects on different forms of pipe configuration as a result of pipe deformation due to usage, huge amount of money will be saved. This will show clearly how the efficiency of a given circular pipe has seriously been affected due to deformation, and the level of loss this has resulted to.

Simulation of Average Turbulent Pipe Flow: A Three-Equation Model

The aim of this study is to evaluate a three-equation turbulence model applied to pipe flow. Uncertainty is approximated by comparing with published direct numerical simulation results for fully-developed average pipe flow. The model is based on the Reynolds averaged Navier-Stokes equations. Boussinesq hypothesis is invoked for determining the Reynolds stresses. Three local length scales are solved, based on which the eddy viscosity is calculated. There are two parameters in the model;one accounts for surface roughness and the other is possibly attributed to the fluid. Error in the mean axial velocity and Reynolds stress is found to be negligible.

Exact Solution of Unsteady Flow of Viscoelastic Fluid in a Pipe with Fractional Maxwell Model

The unsteady flow of viscoelastic fluid in a cylindrical pipe was investigated using the fractional Maxwell model. Two special cases of unsteady pipe flow were expressed. The first is start-up flow, and the second is oscillating flow. The exact solution of start-up flow under a constant pressure gradient was obtained by using the theories of Laplace transform and Fourier-Bessel series for fractional derivatives. The exact solution of oscillating flow was obtained by utilizing the separation of variables.

Two-flow model for piping erosion based on liquid-solid coupling

Previous studies have indicated that piping erosion greatly threatens the safe operation of various hydraulic structures. However, few mathematical models are available to perfectly describe the erosion process due to the complexity of piping. The focus of the present work is to propose a new fluid solid coupling model to eliminate the shortcomings of existing work. A 'pseudo-liquid' assumption is suggested to simulate the particle movement in the erosion process. Then, based on the mass and momentum conservations of the moving particles and flowing water, a new two-flow model is established by using the continuity equations and motion equations. In the model, the erosion rate of soil is determined with a particle erosion law derived from tests results of STERPI. And ERGUN's empirical equation is used to determine the interaction forces between the liquid and the solid. A numerical approach is proposed to solve the model with the finite volume method and SIMPLE algorithm. The new model is validated with the tests results of STERPI. And the soil erosion principles in piping are also explored.

REYNOLDS-STRESS MODELLING OF TURBULENT ROTATING FLOWS

The present analysis shows that the EVM can not reflect the turbulence physics in non-inertial frame. The effects of Coriolis force on turbulence is embodied naturally in the Reynolds-stress transport equation. It is observed that the existing second-moment closure model with appropriate near-wall treatment can adequately predict flows in rotating channel and in axially rotating pipe for moderate rotation rate.

AN ANALYTIC SOLUTION OF DENSE TWO-PHASE FLOW IN A VERTICAL PIPELINE

According to a mathematical model for dense two-phase flows presented in the previous pape[1],a dense two-phase flow in a vertical pipeline is analytically solved, and the analytic expressions of velocity of each continuous phase and dispersed phase are respectively derived. The results show that when the drag force between twophasesdepends linearly on their relative velocity, the relative velocity profile in the pipeline coincides with Darcy's law except for the thin layer region near the pipeline wall, and that the theoretical assumptions in the dense two-phase flow theory mentioned are reasonable.

Numerical modeling of earthen dam breach due to piping failure

Based on model tests of earthen dam breach due to piping failure, a numerical model was developed.A key difference from previous research is the assumption that the cross-section of the pipe channel is an arch, with a rectangle at the bottom and a semicircle at the top before the collapse of the pipe roof, rather than a rectangular or circular cross-section.A shear stress-based erosion rate formula was utilized, and the arched pipe tunnel was assumed to enlarge along its length and width until the overlying soil could no longer maintain stability.Orifice flow and open channel flow were adopted to calculate the breach flow discharge for pressure and free surface flows, respectively.The collapse of the pipe roof was determined by comparing the weight of the overlying soil and the cohesion of the soil on the two sidewalls of the pipe.After the collapse, overtopping failure dominated, and the limit equilibrium method was adopted to estimate the stability of the breach slope when the water flow overtopped.In addition, incomplete and base erosion, as well as one-and two-sided breaches were taken into account.The USDAARS-HERU model test P1, with detailed measured data, was used as a case study, and two artificially filled earthen dam failure cases were studied to verify the model.Feedback analysis demonstrates that the proposed model can provide satisfactory results for modeling the breach flow discharge and breach development process.Sensitivity analysis shows that the soil erodibility and initial piping position significantly affect the prediction of the breach flow discharge.Furthermore, a comparison with a well-known numerical model shows that the proposed model performs better than the NWS BREACH model.

基于三维流动的弯管模型的建立及流场分析

排气歧管是发动机的必要零部件之一,对发动机的性能有很大的影响。文章对排气歧管的弯曲管进行了研究,建立了弯管内气体流动的理论模型,利用FLUENT软件对弯管内气体流动状况进行了仿真,然后对两种弯曲管道(90°-56°管和90°-90°管)中的气体进行了对比分析。结果表明,90°-90°管道内的气体速度分布、压力分布和流线分布更为均匀,流动分离面积和涡流相对较小,速度均匀系数更接近于1,对柴油机进气的影响较小,柴油机的动力性能得以充分发挥。

考虑不同水流交换模式的城市洪涝一维二维双向耦合模型

为准确模拟城市洪涝过程,以地表二维流动模型和SWMM一维管流模型为基础,同时考虑地表径流与地下管流交换的3种模式,构建了城市地表与地下管流双向耦合的水动力学模型。采用水槽试验算例和理论算例对耦合模型进行验证,并将耦合模型应用到英国Glasgow城市街区,分析排水管网和不同地表地下水流交换模式对城市洪涝过程的影响。结果表明:模型在试验算例和理论算例的模拟中均具有较好的精度和可靠性,模型能够准确地模拟具有排水管网的城市洪涝演进过程;与无排水系统相比,检查井简化法、雨水口法和雨水口-检查井法3种水流交换模式下Glasgow城市街区模拟的最大淹没面积分别减少9.3%、23.2%和24.5%,其中对重度积水的消减作用更显著,淹没面积分别减少43.6%、79.9%和80.9%;检查井简化法的消减作用要远小于雨水口法和雨水口-检查井法,后两者差异较小。雨水口法和雨水口-检查井法比较符合实际情况,且雨水口-检查井法的计算效率更高更简单,因此,在城市洪涝模拟中采用雨水口-检查井法考虑地表径流与地下管流交换过程更符合实际。

正弦波形壁面紊流临界分离流动特性的数值研究

波形壁面对波纹管内流动的影响十分显著,其中流动分离对波纹管的流动阻力和传热特性有重要和本质的影响。针对波形比对产生流动分离的影响问题,采用SSTκ-ω紊流模型对不同波形比的正弦型波纹管内流动进行数值模拟,描述了波纹管流的流动特性,分析了波纹管波形比和雷诺数对流动分离的影响。结果表明,在不同波形比的波纹管流中均存在一个流动分离的临界雷诺数,当雷诺数小于临界雷诺数时,波纹管内不会发生流动分离现象;最后拟合得到流动分离临界雷诺数关于波形比的分布公式。研究结果可在一定程度上为波形壁面的工业设计提供参考。

中国首个长期弃置深水油田二次开发技术创新与实践

中国首个长期弃置的深水油田由于二次开发面临复杂的技术难题和较低的经济效益等问题,成为难以动用的边际油田。通过GGRP(地球物理-地质-油藏-生产)一体化技术研究与实践,盘活弃置油田,保障高产稳产。针对剩余油分布的不确定性、构造复杂、储层非均质及水下管汇限温等问题,克服了多项前沿技术难点。这些创新技术包括长期水驱关停油田的剩余油预测技术、复杂油藏的地质导向及精细描述技术、油藏管流耦合模型流动保障技术,成功指导了油田的二次开发,显著提升了油田的开发效果。结果表明:该油田初期产能跃居南海东部油田前三,实际含水上升趋势与方案设计基本一致,预计增加可采储量达259×10^(4)m^(3)。这一开拓性研究为长期弃置深水油田二次开发提供了宝贵的经验,该科技成果在同类油田的开发进程中有着广泛的应用前景。

局部土地利用类型变化对城市水文过程的影响研究

为探究城市下垫面局部土地利用类型变化对城市水文过程的影响,采用高效高精度城市雨洪模型(GAST)耦合管网模型(SWMM),模拟不同降雨重现期下动态改变土地利用类型(单块无下渗土地C_(1)、多块组合无下渗土地C_(2)、单块裸土地C_(3)、单块草地C_(4)和单块林地C_(5))对城市地表积水、管网排水的影响。结果表明:改变局部原始土地利用类型(B1)在小降雨重现期下降低了城市积水量,而在大降雨重现期下改变土地下渗面积和区域位置无法进一步减少积水,此时则需考虑非工程措施的极端暴雨应对模式。不同动态规划区域下渗强度导致管网排口流量增幅不同(C_(2)>C_(1)>C_(3)>C_(4)>C_(5)),隔渗能力越强对管网排口流量增幅影响越大,而管网径流控制率则呈相反趋势。结合对积水量的影响可知,增加下垫面下渗能力并结合排水系统可进一步降低城市内涝风险和管网排水负荷,且管网径流控制率同样可以作为评估动态规划可行性的一个重要指标。

考虑管径因素的中高流速气液两相倾斜管流持液率新模型

为准确得到高流速下倾斜管气液两相管流的持液率,以空气和水为实验介质,设置气量180~2000 m^(3)/h,液量2~20 m^(3)/h,在内径60 mm、长9.5 m的测试管内进行了常压条件下倾斜管高气液两相流实验。实验范围内主要流型是段塞流和环状流,将实验流型绘制到现有流型图中,对比多种流型图发现Mukherjee-Brill、Kaya和Chokshi流型图适用于实验流型的判别。进一步通过实验数据对常用的持液率预测模型进行检验,对比发现Mukherjee-Brill模型相对准确,但误差接近20%,仍然较大。鉴于此,统计国内外高气液流速条件下不同压力、温度、管道直径、管道倾角等参数的文献实验数据,分析总结持液率的影响因素,选择液相黏度准数、管径准数、气相速度准数、液相速度准数、压力准数和倾斜角作为比较序列,持液率作为参考序列,通过灰色关联度分析方法确定管径准数对持液率存在较大影响,从而优化Mukherjee-Brill模型,建立考虑管径影响因素的新持液率计算模型。通过文献实验和本实验高气液流速下包含25.2~95.3 mm共14种管径的数据对新模型进行检验验证,新模型平均绝对百分比误差为6.85%,较现有5种持液率模型至少减少4.96%。

过滤双流体模型的水平管道内稠油输送数值模拟

针对介观尺度下蜡晶颗粒聚团在管壁形成宏观尺度下石蜡层的现象,采用过滤双流体模型研究水平管道输送伴有固态沥青质的稠油的液固两相流流动和传热特性.对比均匀结构曳力模型和亚格子曳力模型的模拟结果,获得了颗粒相时均体积分数、颗粒相压力和过滤传热系数的修正系数等参数分布规律.同时分析了壁面温度对稠油温度分布和传热的影响.结果表明:与均匀模型Gidaspow model相比,过滤模型能够揭示蜡晶颗粒非均匀流动结构对液固两相流的变化规律.Filtered modelⅡ的结果更加接近于试验结果,Filtered modelⅡ的结果随着蜡晶颗粒体积分数的增加而减小.当蜡晶颗粒相体积分数增加到12%时,加入壁面修正的亚格子模型的误差仅为4.1%.而ZAMBRANO等人模拟结果与试验压降的误差为12.9%.亚格子尺度模型能够详细地再现沥青质颗粒聚团的介观尺度流动行为,为稠油输送过程中的蜡晶聚集以及流动过程的预测提供了新的方法.

管道中重质原油流变特性及流动传热规律

因重质原油流动过程存在历史记忆性和全域相关性,经典牛顿本构模型无法有效刻画其流变特性。建立了能够有效刻画重质原油流变特性的空间分数阶本构模型,并基于有限元法数值模拟了原油流动与传热过程。主要研究了空间分数阶模型阶数对原油流动与传热的影响,分析了平均努塞尔数与摩擦阻力系数随着分数阶阶数的变化规律;并比较了管壁热边界条件分别为常壁温与壁面热流密度下,原油传热过程中局部努塞尔数和对流换热系数的变化情况。研究结果表明:随阶数α(α>1)的增大,原油流变性能逐渐向剪切变稀转变,加快了原油流动速度,同时原油传热性能增强,有助于原油的输运效率增加。此外,在壁面热通量条件下的传热效率高于常壁温条件下的传热效率。因此深入研究原油的流变特性以及流动与传热规律,可为提高管道原油输运效率与经济运行提供理论指导。

大城市高架路实测数据分析与交通流模型研究

对上海市中心延安高架路一个路段交通流进行长时间录像拍摄,提取到"车速-车头间距"有效数据26000余对.应用该批实测数据,对多种常见交通流速密关系模型进行比较研究后发现,一维管流模型在我国高速道路交通流参数计算中具有优势.提出采用变参数一维管流模型刻画交通流非线性特征的基本方法.

井孔-含水层系统数值模拟方法研究进展

目前"井孔-含水层"系统处理的三种主要方法:基于线汇理论的井孔模拟、高渗透系数法和渗流-管流耦合模型,评述了各种方法的优缺点,重点指出了传统线源(汇)法理论上的缺陷及实际应用中的局限性。概括了MODFLOW,TOUGH2,FEFLOW等地下水数值模拟软件对井孔含水层模拟的方法;应加强井周小尺度水流水质的精细研究,并研究井周水流运动对水质的作用,以及对大尺度地下水模拟的影响。

管流模型概算法识别大孔道

在疏松砂岩油藏注水开发中后期,大孔道的存在是进一步提高采收率的主要制约因素。文中针对边底水驱油藏特点,在前人研究的基础上,建立了管道流动模型;结合流体的不同流动形态,推导得出了相应的大孔道孔喉直径及渗透率概算公式。在冀东油田高浅北区高104-5区块的应用结果表明,该方法计算结果与井间示踪剂监测及油田开发动态资料均能较好地吻合,具有使用简便、结果可靠、成本低的特点。其对大孔道参数的定量识别,为大孔道封堵技术应用过程中堵剂的选择及用量的确定提供了科学依据。

深层产水气井井筒压力预测研究

井筒压力计算是气井动态分析的重要内容,川西须二段气藏深层气井具备高温、高压、产地层水的生产特征,井筒压力的预测是该气藏动态分析急需解决的难题之一。为此,采用5种常用的气液两相管流模型,对川西气田须二段气藏6口气井进行了9井次的井筒压力计算,并将结果与生产测井的实际资料进行了对比分析。结果表明,常用的H-B模型和M-B模型具有较高的预测精度,基本能满足现场工程计算的需要,在低水气比条件下,H-B模型具有更高的计算精度,在高水气比条件下,M-B模型具有更高的计算精度。