【作者】 石喜；

【导师】 吕宏兴；

【作者基本信息】 西北农林科技大学 ， 水利水电工程， 2013， 博士

【摘要】 管道输水具有输水效率高、施工简便、占地少、维护成本低等优点，目前已成为世界上农业节水的一项关键技术。灌溉管网一般使用PVC、PE等塑料管道，这种管道的承压能力比较低，常常由于阀门、给水栓的快速启闭以及事故停泵等因素，导致管网水锤的发生，引起管道爆裂事故使整个管网系统陷入瘫痪状态。一般情况下，管网中产生水锤的危害比相同激励作用下单管产生的危害要大。随着滴灌、喷灌的不断发展，管道的材料向轻型化的方向发展，管网的结构形式也会越来越复杂，水锤问题将会愈来愈突出。因此开展灌溉管网非恒定流方面的研究对于管网的科学管理、安全运行具有重要意义。本文通过试验与数值模拟对灌溉管网的非恒定流过程进行了研究，作为非恒定流计算的初始条件，之前对恒定流方面的有关内容也进行了探讨。研究的主要内容有：常见PVC三通管和PVC球阀的阻力特性及流动特征研究；简单PVC管网水锤的试验与计算分析；滴灌、喷灌管网的非恒定流建模与分析，水锤防护研究；非恒定流计算程序设计方法研究。得到了以下主要结论：(1)研究了PVC三通管的阻力特性，数据在管网计算中调用。三通管由于边界的影响在分叉处增加了水流的掺混和紊动，使水流提前进入类似圆管沿程阻力系数的阻力平方区，局部阻力系数趋于稳定值的雷诺数约为1.5×105。通过试验与数值模拟得到了常见的7种三通管阻力系数的定量表达式，三通管的局部阻力系数与分流比成二次抛物线关系。引起主管——侧管方向局部水头损失的主要原因是水流方向变化的损失和离心力造成的速度分布变化损失，而引起主管——直管水流方向的主要诱因是在较大分流比时由于水流的剪切和横向环流导致直管分岔处上侧的漩涡运动和流速梯度变化损失。(2)球阀的阻力规律是计算恒定流和非恒定流的重要参数，通过试验与数值模拟得到了5种规格PVC球阀阻力系数随相对开度变化的幂函数表达式。流场分析表明球阀开度较小时在阀体内形成回流区，出现较大的漩涡，导致很大的能量损失。(3)通过建立的管网非恒定流模型与试验结果对比分析表明，采用特征线法求解能较好的模拟管网最大水锤压力值，所有试验工况下管网监测点处计算与试验得到的最大水锤压力相对误差小于14%，但特征线法计算的压力波的衰减规律明显比试验结果缓慢，主要原因是在传统的特征线法计算时摩阻项采用了恒定流摩阻，关于非恒定摩阻在管网计算中的广泛应用还需深入研究。管网最大水锤压力随关闭时间的延长而减小；当关闭时间一定时，不同关闭规律对最大水锤压力的影响不同，其中直线关闭规律产生的最大水锤压力较大，两阶段线性关闭规律产生的压力次之，采用曲线关闭规律产生的压力最小。在两阶段关闭方式中，第一阶段时间较长的操作产生的水锤压力小于第一阶段时间较短的关闭方式。在曲线关闭规律中，幂函数关闭方式产生的压力小于抛物线关闭方式产生的压力。(4)建立了典型滴灌管网和喷灌管网的非恒定流计算数学模型，研究了管段分段最优时间步长的处理方法，提出了用当量毛管代替原来毛管的方法，经过处理后边界水锤波的反射与透射情况与原来相似。典型管网的计算表明几个阀门同时关闭时容易在管网中形成叠加波，最大水锤压力值比无叠加波时的要大；当管网中无叠加波时，管网中的最大水锤压力与操作阀门的距离有关，距离操作阀门越近，最大水锤压力的值越大，紧靠阀门处的压力峰值最大。本算例中管网最大水头一般为稳定流时的2~5倍左右，最大水锤发生的时间为阀门完全关闭后的稍后时间内。从波形的衰减幅度来看，管网中水锤波的衰减较快，明显大于长距离单管输送液体管道的情况，原因可能是管网中支路和节点较多，其水流冲撞作用比较明显、水头损失较大。(5)管网中在操作的阀门前和水泵的出口位置设置空气罐，能使最大水锤压力比无防护时减小30%左右，而且可以有效的控制负压，降低了水锤破坏的几率。(6)针对复杂管网，研究了管网信息的表达与编码设计方法，介绍了基于VisualBasic6.0语言平台管网非恒定流的计算方法，编写了相应的代码。表明设计的程序输入简单，计算、输出方便，可用于实际管网的计算。(7)本文建立的数学模型可方便地计算出整个管网、泵站等每个部位水锤压力波动过程以及最大水锤压力的变化规律，从而指出水锤压力对管网危及的程度、范围和所在位置，为管网的防护工作提供理论依据。更多还原

【Abstract】 The pipeline has become a key technology of water-saving agriculture in the worldbecause of high efficiency, simple construction, less land occupation and low maintenancecosts. The irrigation pipe network always uses PVC、PE and other plastic pipe. The pressureof this pipe is relatively low, with often led broken and made the whole system fall intoparalyzed state by water hammer caused by rapid opening and closing valve and pumpstopped. The water hammer damage generated in network is higher than the same excitationin pipeline. With the development of drip irrigation and sprinkler irrigation, the pipe materialdeveloped to the light direction and the structure of network will be more complex, and thewater hammer problems will be more and more outstanding. So research on the unsteady flowproblems in irrigation network has important significance for correct management and safeoperation.This paper studies the process of unsteady flow in irrigation network by experiment andnumerical simulation. As initial conditions of unsteady flow calculation, the constant flow isdiscussed in prior. The main research content includes: Study on the resistance characteristicsand flow characteristics of PVC tee pipes and PVC ball valve; Study on the water hammer ofsimple PVC pipe network by Tests and analysis; Discuss and build unsteady flow model ofdrip irrigation and sprinkler irrigation pipe network, and research on water hammer protection;Design the calculation program of unsteady flow. The main results are as follows:(1) The resistance of PVC tee pipes was studied and the data was used in the networkcalculation. Due to boundary effects in the bifurcation increased the flow mixing andturbulence, the water flow advanced into the similar pipe drag square zone friction coefficient.The Reynolds number which the local resistance coefficient tended to stable value wan about1.5×105。The resistance coefficient quantitative expression of7kinds of pipes was obtainedby experiment and numerical simulation, which the local resistance coefficient was correlatedwith the flow by second-order parabolic equations. Flow characteristics analysis showed thatthe main reason caused the main branch to side branch due to the loss of direction changesand velocity distribution cause by centrifugal force, and changes main branch to straightbranch was due to the vortex motion and velocity gradient in the straight caused by water shearing and transverse circulation in the large flow ratio.(2) The resistance of ball valve was the important parameter to calculate the steady flowand unsteady flow.5kinds of power function of PVC ball resistance coefficient with openingdegree was obtained by experiment and numerical simulation. The flow field analysis showedthat there has flow region and large vortex in the small opening degree which caused greaterhydraulic losses.(3) Through comparison of experiment and calculation showed that the MOC methodcan better predict the maximum water hammer pressure in pipe network which the relativeerror between experiment and calculation is less than13%. The pressure wave attenuation ofsimulation is slower than experiment because of the constant flow friction is used in thecalculation. The maximum water hammer pressure is reduced with the closing time extension.The maximum water pressure of difference closure rules was distinct, with the linear closingpattern was maximal, the two-stage straight closing pattern by the second, and the curveclosing pattern was lowest. In the curve closing pattern of power function, the pressuregenerated by power function pattern was less than the parabolic closed mode.(4) The unsteady flow mathematical model of drip irrigation pipe network and sprinklepipe network was established and the optimal step processing of pipe segments was studied. Amethod which used the equivalent capillary to replace primary capillary was presented. It wasaffirmed that the processed reflection and transmission of boundary water hammer wave wassimilar to original. The calculation of typical network showed that the double wave was easilyformatted in pipe network when several valve closed simultaneously, and the value ofmaximum water hammer pressure was greater than no overlapping wave. The maximumwater hammer pressure in pipe network was related to the distance of operation value, withthe distance was closer, the pressure was greater. The maximum head of calculation networkwas about2~5times of steady and the maximum water hammer occurred at a time when thevalve completely closed. From the point of view to the wave attenuation, attenuation of waterhammer wave in the pipe network was significantly larger than the long distance pipelineswith conveying fluid because of large nodes and branches in the network which caused muchresistance losses.(5) Arranged air tank in pipe network before operation valve and outlet location of pumpcould decrease the maximum water hammer pressure by about30%, and could control thenegative pressure effectively to reduce the probability of water hammer damage.(6) The network information expression, design method of coding and unsteady flowcalculation in view of the complex network was introduces based on Visual Basic6platformsystem. It showed that the designed procedure with simple input, calculation and convenient output, which can be used to calculate the actual pipe network.(7) The mathematical model established in this paper can be conveniently calculate thewater hammer variation of each part of the whole pipe network, pumping station and the ruleof maximum water hammer pressure, so that indicate the water hammer pressure endangerdegree, range and location to provide a basis for pipe network protection.更多还原