COMPUTER-AIDED ANALYSIS OF UNSTEADY PARTIALLY FILLED FLOWS IN DRAINAGE SYSTEMS

The partially filled pipeflows encountered in drainage systems belong to a family of unsteady flow problems capable of numerical solution via the method of characteristics.The defining equations in terms of flow depth,velocity and surface wave speed are developed and numerically solved by characteristic-difference method with time-lineinterpolation scheme.Boundary conditions for inflow,outflow,moving hydraulic jump and junctions are developed both experimentally and numerically.Full scale model experiments were carried out and it was consequently clarified that numerical model is capable of predicting flow characteristics in realistic drainage networks.     

多层建筑物排水（污）系统非恒定流数学模型

建筑物污水排放系统中的水流为非恒定流，研究其系统中的非恒定流波的传播现象不但对预估管道中的各种水流现象，进行最优设计有着紧密的联系，同时对进一步研究管道中固体物的运动机理及水气两相流问题也有着重要的意义。本文通过应用特征差分方法，数值求解圣维南方程组，对管道中非恒定流进行了分析并建立了相应的计算机程序；对建筑物排污系统常见的边界情况进行了研究，并建立了无量纲的经验公式，这些公式作为边界条件与计算机程序相结合，可直接用于多层建筑物排水系统的模拟及预估     

一维河网非恒定流及悬沙数学模型的节点控制方法

本文的一维河网非恒定流及悬沙数学模型，是根据以一维圣维南方程组，悬沙非平衡输运方程及水位、含沙量节点控制法而建立。首先，利用单一河流有限差分方程组转换形式和节点处质量、能量守恒性，写出所有节点的水位控制方程组。求解此不规则稀疏矩阵方程组得到得有节点的水位，再由单一河流非恒定流的求解方法可获得所有单一河流的断面水位和流量。基于水注的节点水位控制法，本文提出了节点悬沙控制法。假设节点处冲刷或淤积较小，所有节点的含沙量控制方程组可通过输沙量守恒方程用矩阵形式写出。求解此不规则稀疏矩阵方程组，得到所有节点处的含沙量。所有单一河流断面处的含沙量通过单一河流悬沙输运的求解方法获得。本文介绍的模型适用于各种河网类型。作为检验，该模型成功地应用于珠江三角洲流域河网水流及悬沙的数值计算。     

COMPREHENSIVE STUDY OF COMBINING FLOW CONDITIONS AT PIPE JUNCTIONS

ＣＯＭＰＲＥＨＥＮＳＩＶＥＳＴＵＤＹＯＦＣＯＭＢＩＮＩＮＧＦＬＯＷＣＯＮＤＩＴＩＯＮＳＡＴＰＩＰＥＪＵＮＣＴＩＯＮＳ￥ＭａｏＺｅ－ｙｕ（ＨｙｄｒａｕｌｉｃｓＧｒｏｕｐ，ＤｅｐａｒｔｍｅｎｔＯｆＨｙｄｒａｕｌｉｃＥｎｇｉｎｅｅｒｉｎｇ，Ｔｓｉｎｇｈｕａ...     

河网非恒定流隐式方程组的汊点分组解法

本文在现有研究成果的基础上，提出了一种汊点分组解法其特点是能够根据实际问题的需要，灵活方便地将河网中的汊点划分为任意多组，使汊点方程组的系数矩阵压缩到与分组后每组中的汊点数相同的阶数不仅极大地压缩了系数矩阵的贮存量，而且计算量大幅度减少，计算精度也得到了保证     

Unsteady Flow Simulation and Erosion Assessment in a Ditch Network of a Drained Peatland Forest Catchment in Eastern Finland

We developed and applied a computational model for simulating unsteady flow in a drainage network of a boreal forested peatland site. The input to the model was the hourly runoff produced by a hydrological model. The simulations of the flow in the ditch network were performed using an iterative procedure for solving the Saint-Venant equations that govern the flow in each of the network channels. These equations were solved separately for each ditch branch, and the flow depths at the junctions were corrected using the method of characteristics. The model was applied to the drainage network of a peatland catchment in Eastern Finland over a period of 15 months. Because flow resistance in the ditches depended strongly on flow conditions, flow resistance (Manning’s n) was introduced as a function of discharge. The model was calibrated and validated against field data and the simulation results were further applied to assess erosion risk. The highest risk of erosion occurred during long lasting flows induced by snowmelt at ditch sections with a steep slope and a large upstream area. These model results can aid in the design and siting of water protection measures within the drained area.     

高水头船闸输水阀门非恒定流减压试验方法探讨

对船闸输水阀门非恒定流减压试验方法及其成果进行了初步评估。阐述了船闸输水阀门非恒定流减压试验方法提出的缘由。简要地介绍了国内外首座船闸专用非恒定流减压试验设备。总结了非恒定流减压试验的特点，并对恒定流与非恒定流两种减压试验方法的差异进行了初步分析和比较。     

大藤峡水利枢纽船闸中间渠道非恒定流三维数值模拟研究

采用两相流模型,辅以RNGk-ε湍流模型来模拟双级船闸中间渠道的水力特性,对于自由水面的模拟采用了VOF法.通过对中间渠道中非恒定流的三维数值模拟,主要针对波速、振荡波高、局部水面比降、渠道流速等水力要素进行分析,给出了上、下级船闸不同运转方式下的水力特性,为工程设计提供依据,且可为今后类似工程提供参考和借鉴.     

平原城市自排区排涝模数计算方法研究

针对平原城市自排区的排涝特点,通过分析几种排涝计算方法的原理及计算结果,提出了适用于平原城市自排区排涝模数计算的一维非恒定流法。以安徽省宿州市主城区为例,分别采用平均排除法、割平头法和非恒定流法计算其排涝模数。结果表明：非恒定流法更适用于平原自排区排涝模数的计算,为城市排涝提供了依据。     

ANALYSIS OF HYDRODYNAMICS FOR TWO-DIMENSIONAL FLOW AROUND WAVING PLATES

Hydrodynamic characteristics for two-dimensional flow around a waving plate are investigated. Under large Reynolds number approximation, the flow is assumed to be a combination of the outer potential flow and a thin vortex layer, which consists of a boundary layer and a shed free shear layer. A nonlinear mathematical formulation for describing the outer unsteady potential flow coupled with an unsteady boundary layer equation for the inner viscous flow adjacent to the waving plate is developed. A semi-analytical method with a nonlinear Kutta condition imposed at the trailing edge is used to solve the velocity field of the outer flow and the evolution of wake vortex induced by a large-amplitude waving plate. The unsteady boundary layer equation is solved by extending Pohlhausen’s method to its unsteady counterpart. The thrust and viscous drag coefficients, propulsive efficiency, and the pattern of wake vortex sheet are discussed.     

Numerical predictions of pressure pulses in a Francis pump turbine with misaligned guide vanes

Previous experimental and numerical analyses of the pressure pulse characteristics in a Francis turbine are extended here by using the unsteady Reynolds-averaged Navier-Stokes equations with the shear stress transport （SST） turbulence model to model the unsteady flow within the entire flow passage of a large Francis pump turbine with misaligned guide vanes at the rated rotational speed. The S-curve characteristics are analyzed by a combined use of the model test and the steady state simulation with the aligned guide vane firstly. Four misaligned guide vanes with two different openings are chosen to analyze the influence of pressure pulses in the turbine. The characteristics of the dominant unsteady flow frequencies in different parts of the pump turbine for various misaligned guide vane openings are investigated in detail. The predicted hydraulic performance and the pressure fluctuations show that the misaligned guide vanes reduce the relative pressure fluctuation amplitudes in the stationary part of the flow passage, but not the runner blades. The misaligned guide vanes have changed the low frequencies in the entire flow passage with the change of the pulse amplitudes mainly due to changes in the rotor-stator interaction and the low frequency vortex rope flow behavior.     

水电枢纽下泄非恒定流作用下的航道整治研究

水电枢纽下泄非恒定流具有日水位、流量频繁大幅波动的特点,对下游河道的河床演变与通航条件产生了严重影响。针对枢纽下泄非恒定流作用下河床演变与航道整治的特点,建立了贴体正交曲线坐标系统下的韩江上游二维水沙数学模型;在运用大量水沙实测资料对模型详细验证的基础上,对推荐方案实施后的整治效果与非恒定流对航深的影响进行了计算。     

液体管道高频水力瞬变过程的数值模拟

目前在液体管道高频水力瞬变分析中,人们通常采用经典的拟稳态摩阻模型进行分析.但这种方法针对管壁切应力具有拟稳态特性的缓慢瞬变的分析是可行的,而对高频瞬变流动过程而言却不能准确预测水击压力波具体的衰减过程以及出现的波形畸变现象.介绍了一种新的考虑瞬时加速度对高频水力瞬变过程影响的非恒定摩阻模型,并结合特征线法给出了其数值解法,最后通过实例验证了该模型能比经典的拟恒定摩阻模型更为准确地模拟液体管道中高频瞬变流压力波的衰减和波形畸变.该模型对计算机的要求和计算耗时与经典的拟稳态摩阻模型相差不大,是一种具有良好工程应用潜力的液体管道高频瞬变分析数学模型.     

NUMERICAL SIMULATIONS OF 2D PERIODIC UNSTEADY CAVITATING FLOWS

1. INTRODUCTION Cavitation is a natural phenomenon especially existing in liquids. A cavitating flow generally involves a large number of vapor structures such as bubbles or vortices which are convecting downstream. When they reach high pressure zones, th…     

A NEW APPROACH TO THE SIMULATION OF UNSTEADY SUBCRITICAL FLOW

ＡＮＥＷＡＰＰＲＯＡＣＨＴＯＴＨＥＳＩＭＵＬＡＴＩＯＮＯＦＵＮＳＴＥＡＤＹＳＵＢＣＲＩＴＩＣＡＬＦＬＯＷ￥ＭａｏＺｅ－ｙｕ（ＤｅｐａｒｔｍｅｎｔｏｆＨｙｄｒａｕｌｉｃＥｎｇｉｎｅｅｒｉｎｇ，ＴｓｉｎｇｈｕａＵｎｉｖｅｒｓｉｔｙＢｅｉｊｉｎｇ１０００８...     

On the hydrodynamics of hydraulic machinery and flow control

Hydraulic machinery mainly includes turbine and pump, which is closely related to national economy and people's livelihood involving aerospace industry, marine engineering, hydropower engineering, petroleum industry, chemical industry, mining industry, biomedical engineering, environmental engineering, agricultural water-soil engineering, etc.. The internal flow of hydraulic machinery is extremely complex, and its characteristics can be summarized as high Reynolds number, multi-scales, inhomogeneous and vortex-dominant unsteady turbulence which interact with the rotating dynamic boundary(rotor blade). Based on the analysis of the internal flow characteristics of hydraulic machinery, the author and his research team successively proposed a rotation correction model, a curvature corrected filter-based model, a scalable detached eddy simulation method, and a non-linear hybrid RANS/LES turbulence model to capture unsteady flow structures and then predict hydraulic performance and dynamic characteristics more accurately. According to the analysis on the internal flow, the corresponding flow control measures were put forward. It was verified by experiments that these methods could significantly improve the hydraulic performance, anti-cavitation performance and dynamic characteristics(pressure pulsation and vibration) of hydraulic machinery in a certain range of operating conditions. In addition, the mechanism how flow control measures influence internal flow was analyzed in depth, aiming at finding a feasible and effective way to improve hydraulic performance, anti-cavitation performance and dynamic characteristics of hydraulic machinery.     

NUMERICAL SIMULATION OF FLOW OVER TWO SIDE-BY-SIDE CIRCULAR CYLINDERS

In the present paper, the unsteady, viscous, incompressible and 2-D flow around two side-by-side circular cylinders was simulated using a Cartesian-staggered grid finite volume based method. A great-source term technique was employed to identify the solid bodies (cylinders) located in the flow field and boundary conditions were enforced by applying the ghost-cell technique. Finally, the characteristics of the flow around two side-by-side cylinders were comprehensively obtained through several computational simulations. The computational simulations were performed for different transverse gap ratios (1.5≤T/D≤4) in laminar (Re=100,200) and turbulent (Re=104) regimes, where T and D are the distance between the centers of cylinders and the diameter of cylinders, respectively. The Reynolds number is based on the diameter of cylinders,D. The pressure field and vorticity distributions along with the associated streamlines and the time histories of hydrodynamic forces were also calculated and analyzed for different gap ratios. Generally, different flow patterns were observed as the gap ratio and Reynolds number varied. Accordingly, the hydrodynamic forces showed irregular variations for small gaps while they took a regular pattern at higher spacing ratios.     

三峡电站调峰流量对航运的影响分析

针对三峡—枝城河道的地形特征,建立一维非恒定流模型.在三峡电站预先给定的航运约束条件下,计算电站下游的非恒定流对航运的影响并对若干调峰流量过程曲线进行分析,找出满足航运要求的调峰曲线.提出可调整葛洲坝的库容水位关系,对三峡调峰流量进行反调节,削峰填谷,以满足航运要求.     

双线船闸引航道水力特性数值模拟

长沙综合枢纽双线船闸共用引航道,船闸引用流量大,在灌、泄水时引航道内形成非恒定流,水流十分复杂.为确保引航道内船舶航行和停泊安全,采用三维数学模型对船闸最不利运行工况下引航道内复杂非恒定流进行了深入研究,分析了复杂水流形成机理、发展和传播过程,获得了不利工况下的波高、波速、比降和系缆力等水力要素,提出并研究了双线船闸错峰运行和增加船闸旁侧泄水等改善措施,有效改善了引航道内水流条件.研究成果已应用于依托工程中,船闸试运行表明研究提出的改善措施十分有效,该成果可供类似工程参考借鉴.     

水轮机活动导叶关闭过程中导水机构内动态流场数值模拟研究

水力机组在暂态过程中诱发的强瞬变流是一种复杂的非定常湍流,对机组安全稳定运行具有重要影响。为了探索水轮机活动导叶动态调节动作诱发叶后强瞬变流对机组暂态特性的影响,本文应用模拟流固耦合动态效应较好的浸入边界法和大涡模拟技术来处理该类强非线性动边界流体动力学问题。首先,精细模拟槽道内两级线性排列动静叶栅动态绕流叶后压力和尾迹结构分布,由于受到固定导叶和活动导叶动静干涉的影响,其下游流场表现出复杂的非定常流动特征。随后完成了水轮机导水机构两级非线性环列叶栅动态绕流的模拟,展现了水轮机导叶调节运动的关闭过程。该方法可用于水轮机流道内多级翼型叶栅绕流的精细模拟,为研究水轮机调节振荡对机组暂态性能的影响提供有益的参考,对耦合上游管道系统水力暂态和水轮机三维暂态效应的研究也有指导意义。