A MODIFIED SIMPLE ALGORITHM FOR 2-D FLOW IN OPEN CHANNEL

1.　INTRODUCTIONSince the SIMPLE[1 ] algorithm was set up,it has been used to numerically simulateincompressible flow successfully.And later on,the improved algorithms such as SIMPLERalgorithm[2 ] and SIMPLEC algorithm[3] have been presented in succession.For all thealgorithms stated above,only when velocity field varies linearly with water pressure(i.e.,pressure flow) ,owing to the coefficients of the velocity correction formulae beingindependent of pressure,do the velocity corre…     

求解守恒形式的二维浅水方程的SIMPLE类程式

对二维浅水方程守恒形式，采用控制体积法离散，可得流速与水深的耦合关系.据此，本文在SIMPLE类程式的基础上，提出一种新的、具有更快收敛速度的流速校正公式.作为测试算例，对由两种不同底坡组成的棱柱形明渠水流进行了数值模拟，取得了预期的效果。     

矩形明渠边界平均剪切应力变化规律研究

针对棱柱型矩形明渠的特点 ,在分析均匀流运动机理的基础上 ,认为水流可以分为河床作用部分和岸壁作用部分 ,各部分分别作均匀流运动。在分析水体能量消耗的物理模式的基础上 ,提出了面积分割的补充关系。对于河床和岸壁糙率相同的情况 ,利用静力平衡条件和水流连续方程 ,可推得水流槽底、岸壁剪应力的计算关系式。对关系式的讨论表明 ,公式结构合理 ,能反映明渠水流的特点。对已有水槽试验资料进行的分析表明本文提出的计算关系式较好地描述水流的实际情况 ,比已有的公式更简便可靠。     

Theoretical analysis and numerical simulation of mechanical energy loss and wall resistance of steady open channel flow

The mechanical energy loss and the wall resistance are very important in practical engineering. These problems are investigated through theoretical analysis and numerical simulation in this paper. The results are as follows.(1) A new mechanical energy equation for the total flow is obtained, and a general formula for the calculation of the mechanical energy loss is proposed.(2) The general relationship between the wall resistance and the mechanical energy loss for the steady channel flow is obtained, the simplified form of which for the steady uniform channel flow is in consistent with the formula used in Hydraulics deduced by ? theorem and dimensional analysis.(3) The steady channel flow over a backward facing step with a small expansion ratio is numerically simulated, and the mechanical energy loss, the wall resistance as well as the relationship between the wall resistance and the mechanical energy loss are calculated and analyzed.     

射流冲刷试验研究(之二)

根据室内试验结果 ,建立了一个能够统一表达圆形喷嘴和矩形喷嘴射流强度的公式 ,建立了由射流产生的冲刷坑的几何尺度与射流强度间的关系。对试验中发生的喷嘴临界提升高度从理论上分析了存在的合理性。依据分析建立的喷嘴在临界提升高度和最大提升高度之间的冲刷坑尺度与射流强度、倾角和提升高度间的关系能够较好地描述试验结果。     

水库三角洲河道输沙之研究

水库进口附近三角洲河道之水流系近似均匀流，并非真正之均匀流。三角洲河道动床之自我调整作用，因水库水位之回水影响，其输沙特性有异于明渠均匀流，传统上，将明渠均匀流平衡条件之下输沙公式应用于估算的三角洲河道之输沙能力，似有其不稳定性。本研究进行一系列水流区输沙试验，并纳入文献「１０」Ｈｏｔｃｈｋｉｓｓ之试验数据一并分析。     

挟沙水流的冲刷率及河床惯性的研究

在清水水流河床冲刷率的实验研究基础上，本文进一步研究了挟涉水流来沙率对冲刷率的影响。结果说明挟抄水流的冲刷率随来沙率与水流输沙力欠饱和度之比以负指数律降低。当来水挟抄率与水流饱和输抄率相等时，冲刷率降刊0。河床惯性是河床在非恒定流中一种重要的动力学性质。利用河床惯性与冲刷率的关系测量了各种沙样的河床惯性值。发现河床惯性随床沙颗粒分选系数增大而增大，分选系数很大时趋近于极限值50t／Tn0。利用河床惯性和河床变形方程得出了冲刷过程中水流输沙率沿程和随时间的变化规律，结果说明水流输沙率欠饱和度向下游以负指数律下降，这与冲刷率随实际水流挟沙率与欠饱和度之比以指数率下降的规律有耜同意义。河床惯性愈大，实际水流输沙率增长得愈慢。河床惯性与于容重及摩阻流速之比构成的无困次数A。代表河床变形和水流实际挟沙量对水流挟沙力变化的响应程度。     

河道冲刷和清水水流河床冲刷率

在冲积河流里。水流条件变化如洪水、水库泄放清水、河道渠化等使挟沙力不饱和引起冲刷，称为河道冲刷。这与水工建筑造成的局部冲刷不同。河道冲刷深度主要决定于冲刷率和冲刷历时。本研究通过对各种泥沙大量实验，证明了河床冲刷率正比于水流提供的冲刷功率并依赖于泥沙粒径和容重，首次提出了冲刷率公式。经验证，该公式可以用于非恒定流输沙和河流洪水冲刷计算。     

Influence of bed elevation discordance on flow patterns and head losses in an open-channel confluence

Confluences play a major role in the dynamics of networks of natural and man-made open channels,and field measurements on river confluences reveal that discordance in bed elevation is common.Studies of schematized confluences with a step at the interface between the tributary and the main channel bed reveal that bed elevation discordance is an important additional control for the confluence hydrodynamics.This study aimed to improve understanding of the influence of bed elevation discordance on the flow patterns and head losses in a right-angled confluence of an open channel with rectangular cross-sections.A large eddy simulation(LES)-based numerical model was set up and validated with experiments by others.Four configurations with different bed discordance ratios were investigated.The results confirm that,with increasing bed elevation discordance,the tributary streamlines at the confluence interface deviate less from the geometrical confluence angle,the extent of the recirculation zone(RZ) gets smaller,the ratio of the water depth upstream to that downstream of the confluence decreases,and the water level depression reduces.The bed elevation discordance also leads to the development of a large-scale structure in the lee of the step.Despite the appearance of the large-scale structure,the reduced extent of the RZ and associated changes in flow deflection/contraction reduce total head losses experienced by the main channel with an increase of the bed discordance ratio.It turns out that bed elevation discordance converts the lateral momentum from the tributary to streamwise momentum in the main channel more efficiently.     

顺坡渐扩矩形明渠水跃计算公式

顺坡渐扩矩形明渠常被用在排水工程中作为排水口与河道的连接段。由于河道水位变化,水跃将发生在连接段。本文从动量守恒原理出发推导了顺坡渐扩矩形明渠水跃方程,在假定水跃水质点作二维运动和水跃段内质点垂向加速度近似为常量的基础上推导了水跃长度近似计算公式。并与扩散角为9°、水平坡度角为6°特定条件的模型试验结果进行了对比,结果吻合良好,可供类似工程参考。     

3D CFD validation of invert trap efficiency for sewer solid management using VOF model

Earlier investigators have numerically carried out performance analysis of the invert trap fitted in an open channel using the stochastic discrete phase model(DPM) by assuming the open channel flow to be closed conduit flow under pressure and assuming zero shear stress at the top wall.This is known as the fixed lid model.By assuming the top wall to be a shear free wall,they have been able to show that the velocity distribution looks similar to that of an open channel flow with zero velocity at the bottom and maximum velocity at the top,representing the free water surface,but no information has been provided for the pressure at the free water surface.Because of this assumption,the validation of the model in predicting the trap efficiency has performed significantly poorly.In addition,the free water surface subject to zero gauge pressure cannot be modeled using the fixed lid model because there is no provision of extra space in the form of air space for the fluctuating part of the water surface profile.It can.however,be modeled using the volume of fluid(VOF) model because the VOF model is the appropriate model for open channel or free surface flow.Therefore,in the present study,three-dimensional(3D) computational fluid dynamics(CFD) modeling with the VOF model,which considers open channel flow with a free water surface,along with the stochastic DPM.was used to model the trap efficiency of an invert trap fitted in an open rectangular channel.The governing mathematical flow equations of the VOF model were solved using the ANSYS Fluent 14.0 software,reproducing the experimental conditions exactly.The results show that the 3D CFD predictions using the VOF model closely fit the experimental data for glass bead particles.     

峡岛湍流海域水流力荷载计算方法探讨

与常规明渠流断面流速对数分布形态不同,外海连岛间海域断面流速呈现出复杂的分布特征,其主要原因在于凹凸不平海床面对海域流场分布有很大的影响。通过室内模型试验发现,峡岛湍流海域垂线流速基本呈二次抛物线分布形态,随后通过分析计算提出了以等效坡度为主因子的湍流流速分布公式。该公式计算结果与现场实测结果比较吻合,同时还给出了以抛物线分布形态为基准的水流力荷载计算修正系数。研究成果可为峡岛海域的工程结构设计提供参考。     

受边壁影响的矩形光滑明渠垂线流速分布研究

当明渠宽深比较小时,由于边界剪切应力分布不再是均匀的。垂线流速分布由底向上,从某一高度开始,在该点以下为对数分布,在该点以上为抛物线分布。本文在已有研究理论的基础上,验证了流速最大点位置α分布公式的正确性,提出了光滑矩形明渠各垂线上流速分布的新抛物线公式。     

180°弯曲水槽内床面冲淤演化过程数值模拟

为准确掌握180°弯曲水槽内床面冲淤特征及其演化过程,采用基于非结构化三角形网格的三维流动和地形冲淤数值模型对180°弯曲水槽内床面的冲淤演化过程进行复演。运用标准k-ε紊流模型和显式2步投影方法求解RANS方程,推移质输沙率选取VanRijn输沙公式计算,对于二次流强度较强、横向坡度对输沙方向影响较大的强弯曲水槽,采用方便实用的Engelund方法计算横向底坡所引起的输沙方向的偏移,同时对河床变形所引起的河床临界起动切应力变化进行修正及对流动和地形冲淤相同时间步模拟非恒定的河床冲淤演化过程。与试验测量结果对比显示数值模型对强弯曲水槽冲淤特征有较好的模拟效果;Engelund方法对计算输沙方向偏移角度具有明显的改进;模型同样也具备复演内床面非恒定冲淤演化过程的能力。     

壅水条件下水流阻力试验研究

壅水条件下的水流阻力及输沙特性,在水利工程的应用中占有十分重要的位置。对壅水条件下河道开展概化水槽试验,采用声学多普勒测速仪ADV对水流流速进行了测量,并对壅水条件下水流阻力和床面切应力等进行了分析。结果表明壅水条件下,水流流速沿垂线分布较均匀流条件下更加均匀,当壅水程度越大时,水流流速沿垂线分布越均匀,且流速分布大致上仍服从对数率分布;壅水条件下,随着水深的增大,摩阻流速不断减小;壅水条件下河道水流阻力系数随着非均匀系数及水力半径的增大而增大;引入壅水程度指标,并拟合得到了床面切应力随壅水程度指标的变化关系式。成果可为壅水条件下水流结构特征及输沙规律的研究提供参考。     

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.     

Flume study of the hydraulic effects of large woody debris in lowland rivers

As a part of a study investigating the hydraulic effects of large woody debris (LWD) in lowland rivers, a series of small-scale experiments were conducted in a rectangular glass-walled recirculating flume. These experiments were undertaken to determine the order of magnitude of the increase in flood levels caused by LWD at different positions within a channel cross-section. Position variables that were considered in these experiments were height above bed, angle to flow direction, and separation distance in the direction of flow. This study was undertaken to quantify the hydraulic benefits (primarily reduced flood levels) gained by the removal of LWD from lowland rivers, which is a common practice in several countries. From an integrated river management perspective it is necessary to weigh any hydraulic benefits of LWD removal up against the environmental costs of loss of faunal habitat, and possible geomorphic instability. The results of these experiments indicate that the levels of LWD commonly occurring in the lowland rivers of southeastern Australia seldom cause any significant effect on flood levels. However, where LWD occur at channel constrictions, or where unusually high densities of LWD are present, the effect on flood levels will be significant.     

PIV EXPERIMENTAL RESEARCH OF FLOW STRUCTURE IN RECTANGULAR CHANNEL WITH TRANSVERSELY PLACED SPIRAL COIL INSERT

The flow field in a rectangular channel with a transversely placed spiral coil insert is investigated by Particle Image Velocimetry (PIV) measurements in both transverse and longitudinal sections. The experimental results show that multi-longitudinal vortices are induced downstream of the spiral coil and are distributed as a symmetrical vortex array along the horizontal central line of the transverse section. Along the mainstream, due to the spiral motion of the longitudinal vortices, the velocity fluctuates in a manner of the damped sinusoidal curve and the velocity component in the wall normal direction is improved in the channel. Compared with the flow field in a smooth channel it is found that the movement of the longitudinal vortices can cause a continuous disturbance near the channel walls and thus enhances the fluid velocity in the near wall region, which consequently leads to the reduction of the velocity gradient and a more uniform velocity distribution. With the increase of the Reynolds number, the induced longitudinal vortices gain strength and become straighter and closer to the channel walls, thus the turbulence intensity is further enhanced in this area.     

明渠湍流床面附近跃移层面颗粒浓度垂线分布

本文以动理学理论的Boltzmann方程为基础，考虑明渠湍流床面附近猝发喷射和清扫运动对跃移层内运动颗粒的不同作用，分析了明渠中泥沙颗粒浓度垂线分布问题，得到了适用于包括跃移层、悬移层在内的统一浓度垂线分布公式。文中着重研究了跃移层内运动颗粒的浓度垂线分布，并将本文结果与实测跃移层内浓度垂线分布及实测跃移层顶部浓度进行了对比，结果表明理论与实验两者符合较好。     

明渠岸边横向取水口的三维数值计算

本文是在明渠岸边横向取水口的试验研究基础上的配套数值模拟。采用雷诺平均的N—S方程，以各向异性的雷诺应力模型(RSM)封闭方程组，用SIMPLEC算法对压力—速度场求解。计算结果与试验实测结果吻合较好，反映了此项模拟的可信性，可籍以扩大、分析一些运动规律。数值计算结果启示了横向取水口水流的复杂三维流动特性，据之对取水口附近水流各区的划分、水流的分离和反向流动、螺旋流以及床面剪应力的分布等复杂水力和泥沙输移物理现象有了进一步认识。