共查询到20条相似文献，搜索用时 890 毫秒
1.
Total energy loss assessment for trickle lateral lines equipped with integrated in-line and on-line emitters 总被引：4，自引：3，他引：1
Gürol Yildirim 《Irrigation Science》2010,28(4):341-352
The accurate evaluation for the pressure head distribution along a trickle (drip) irrigation lateral, which can be operated
under low-pressure head, dictates to precisely determine the total energy (head) losses that incorporate the combined friction
losses due to pipe and emitters and, the additional local losses, sometimes called minor losses, due to the protrusion of
emitter barbs into the flow. In routine design applications, assessment of total energy losses is usually carried out by assuming
the hypothesis that minor losses can be neglected, even if the previous experimental studies indicated that minor losses can
become a significant percentage of total energy losses as a consequence of the high number of emitters (with reducing the
emitter spacing) installed along the lateral line. In this study, first, simple mathematical expressions for computing three
energy loss components—minor friction losses through the path of an integrated in-line emitter, the local pressure losses
due to emitter connections, and the major friction losses along the pipe—are deduced based on the backward stepwise procedure,
which are quickly implemented in a simple Excel spreadsheet, to rapidly evaluate the relative contribution of each energy
loss component to the amount of total energy losses. An approximate combination formulation is finally proposed to evaluate
total energy drop at the end of the lateral line. For practical purpose, two design figures were also prepared to demonstrate
the variation of total friction losses (due to pipe and emitters) with emitter local losses, and the variation of pipe friction
losses with emitter minor friction losses, versus different emitter spacing ranging from 0.2 to 1.5 m, and various total number
of emitters, regarding two kinds of the integrated in-line emitters. Comprehensive comparison test covering two design applications
for different kinds of integrated in-line and on-line emitters indicated that the present mathematical model is simple, can
be easily adaptable, but sufficiently accurate in all design cases examined, in comparison with the alternative procedures
available in the literature. 相似文献
2.
通过试验研究了标准管径16 mm的5种内镶贴片式滴灌带的局部水头损失,分析了滴灌带局部水头损失占沿程水头损失的比值hjt/hf和局部水头损失系数α的变化规律.结果表明:相同工作压力下,滴灌带当量直径随壁厚的增大而减小,造成沿程水头损失和局部水头损失的增大,局部水头损失与壁厚、滴头断面面积和雷诺数有关.随着雷诺数的增大,滴灌带局部水头损失占沿程水头损失的比值hjt/hf减小,最小值可达到0. 67,但仍超过中国制定的微灌工程技术规范设计标准(0. 1~0. 2).通过对试验数据进行多元回归分析,提出了滴灌带局部水头损失系数与过水断面收缩比和雷诺数的关系式,相关系数为0. 96. 相似文献
3.
Analysis of factors affecting the availability of air bubbles to subsurface drip irrigation emitters during oxygation 总被引：3，自引：0，他引：3
In this study, we sought to define system features that impact air delivery in subsurface drip irrigation systems. A 58 % decrease in emitter cross-sectional area caused a 71 % reduction in the water flow rate, but the 37 % decrease in emitter air flow rate was statistically non-significant. For emitters with symmetric connectors, delivery of air from the emitters depended on the length of the connector relative to the air layer flowing at the top of the pipe. Emitters with asymmetric connectors yielded greater air flow rates compared to those with symmetric connectors, a result ascribed to a low-pressure region at the tip of asymmetric connectors. When symmetric connectors were used, an increase in pipe diameter was directly related to an increase in the uniformity of emitter air flow rate distribution expressed by the Christiansen uniformity coefficient (CUC), and inversely related to the efficiency of air bubble delivery and mean emitter air flow rate. In contrast, when asymmetric connectors were used, an increase in pipe diameter was associated with a decrease in CUC, and an increase in the efficiency of air bubble delivery and mean emitter air flow rate. 相似文献
4.
微孔渗灌管水力特性的试验研究 总被引：1，自引：0，他引：1
通过试验实测的方法,对埋入地下的微孔渗灌管灌水时管路的水力特性进行了研究。结果表明,随着进水口压力、管长和微孔渗灌管透水性能的增加,微孔渗灌管水流量、沿程的水头损失和水力偏差率增大,且水头损失主要发生在微孔渗灌管靠近进水口的前半段。实际设计管网时,应综合考虑供水压力、渗灌管透水性能对水头损失的影响,确定管网中毛管的长度,保证灌水均匀度。 相似文献
5.
A computer model, SPRINKMOD, was tested with field data collected from a simple sprinkler irrigation system in operation.
The original data for laterals and the amount and way leakage is considered were modified to evaluate the model sensitivity.
The model predicted the pump station flow rate within 2% and the pump station pressure head within 5% with the original data
collected. For this irrigation system, no practical effect was observed in the system operating point by changing the lateral
pipe characteristics, lateral leakage amount and distribution, lateral pipe roughness and lateral local loss coefficient for
flow past a riser outlet. The amount of leakage had more effect on the model simulation of pressure heads than the way leakage
was considered, localized or distributed along the laterals. The use of a variable local loss coefficient, K
r, along the 350-m hand-move laterals had a negligible effect on both system operating point and distribution of pressure heads
along the laterals.
Received: 14 February 1998 相似文献
6.
薄壁微喷带沿程水头损失试验研究 总被引：2，自引：0，他引：2
【目的】研究薄壁型微喷带沿程水头损失的水力性能。【方法】采用控制变量法与L9(34)正交试验方案,对折径为N43、N45、N50、N64 mm的微喷带进行沿程水头损失水力性能试验,获取流量、长度、折径与水头损失等试验数据,分析流量、长度、折径三因素对沿程水头损失的影响程度以及水头损失相关水力性能参数,提出了沿程阻力系数,对沿程水头损失计算公式参数进行修改,得出了薄壁型微喷带水头损失计算参数。【结果】薄壁型微喷带沿程水头损失随着压力与铺设长度的增大而增大;折径、流量、长度的F值分别为90.314、26.056、19.041,表明对沿程水头损失影响依次减小。【结论】采用修改后的沿程水头损失计算参数计算薄壁型微喷带沿程水头损失值与试验值吻合较好。 相似文献
7.
采用小孔扩散方式所建立的轴对称二维切片模型和二维轴对称数值模型,对抽水工况的出流特性和尾流的水流摆向进行了研究.试验与数值模拟结果显示,抽水工况下出流可视作射流,水流摆向与水位有一定关系,高水位时摆向河床,低水位时摆向水面;三维模型对比试验显示,抽水工况下采用防涡板结构时的进/出水口水头损失系数可达0.61,而无防涡梁、阶梯防涡梁和水平防涡梁等3种结构的水头损失系数范围为0.44~0.48;发电工况下水头损失系数均接近0.40.试验结果显示,竖向扩散段的扩散角小于9°时能保证配水均匀.采用2~3倍发电流量观察发电工况时漩涡的形成,试验显示漩涡的变化特征随水位发生变化：高水位时在进/出水口顶盖上部形成单一的漩涡;当水位降低到一定程度后,大环流转化为若干个漩涡,漩涡数量与导流墩数量相同.两个进/出水口同时运行时,环流之间相互干扰,可能形成一顺一逆环流. 相似文献
8.
9.
为了提高滴灌系统水力设计的准确性,基于有限元原理,提出一种计算薄壁内镶贴片式滴灌带能量损失和灌水均匀度的方法,局部水头损失根据贴片式滴头结构、管内压力和管道壁厚确定,沿程水头损失通过改进Darcy－Weisbach公式编写计算机程序,分析了不同滴灌带的水头损失及均匀度变化规律,并与《微灌工程技术规范》中推荐计算方法的结... 相似文献
10.
A computer model, SPRINKMOD, was tested with field data collected from a complex sprinkler irrigation system in operation.
The original data collected were adjusted in order to calibrate the model for the irrigation system. Five modifications were
made in the original data so that the model sensitivity could be evaluated. The model predicted the system operating point
with less than 1% error, after some adjustments in the data. The relative mean standard error was 4.1% for the upstream pressure
heads and 2.1% for the downstream pressure heads of all laterals analyzed together. Measurement of pressure and discharge
at pump stations along with a reasonable estimate of leakage appears to be essential for simulation of old systems. Adjustments
made to pipe wall thickness and pipe roughness were not as important as the adjustments made to the lateral valves closure
in getting SPRINKMOD to simulate pressure heads that were close to the measured values. For long laterals, like center pivot
laterals, a variable local loss coefficient for flow past a riser outlet worked better than a fixed value of 0.3.
Received: 24 November 1997 相似文献
11.
12.
《Agricultural Water Management》2005,75(3):184-193
The low efficiency water control provided by sluice gates and weirs used in the flooded rice tillage system in Rio Grande do Sul, Brazil, have caused significant water losses. Such devices are utilized to control the water flow from the main to the secondary channels. The water flow through the gates is highly influenced by the water depth fluctuation in the main channel. The purpose of this work was to construct and evaluate a flow regulator to reduce flow variations in the secondary channels, resulting from water level fluctuation in the main channels. The prototype operates with a float that prevents the water head variation over the water passage orifices. The regulator flow control was compared to the sluice gate flow control. Both structures were installed at a lateral inlet, and the depth of water in the main channel ranged from 70 to 90 cm. The flows from the regulator and sluice gate were measured with “H” flumes. To relate the flow provided by the regulator to the water head over the water passage orifices, the regulator was submitted to six different water heads, ranging from 5 to 30 cm. The comparison between the structures showed that both presented variation in the controlled flow. However, the flow control provided by the automatic flow regulator was more effective than that provided by the sluice gate. The controlled flow variation was 5.5% for the automatic flow regulator, and 23.7% for the sluice gate. Regulator flow analysis for the different water heads showed that it can operate with flows ranging from 24 to 49 L s−1. Comparing the sluice gate to the automatic flow regulator, the latter is a more efficient flow control device, reducing the waste of water. 相似文献
13.
14.
为研究竖井贯流泵中竖井部分对贯流泵装置的水力性能的影响,采用计算流体动力学方法对包含进出水延长段、进出水流道、叶轮和导叶在内的整体泵装置进行数值模拟,分析竖井长度、竖井头部型线以及竖井尾部型线对进水流道水力损失、出口断面轴向速度分布均匀度、出口断面速度加权平均角以及泵装置能量特性的影响.结果表明:竖井长度、竖井头部和尾部型线对进水流道水力损失和出口断面速度加权平均角有影响,但是对进水流道出口断面轴向速度分布均匀度几乎没有影响;竖井尾部型线对流道水力损失影响最为显著,在设计流量工况下,竖井头部和尾部皆为锥形型式的进水流道水力损失较头部和尾部皆为圆弧形型式的进水流道的水力损失小24%;竖井头部型线和尾部型线采用锥形型式的进水流道水力性能更优,但是在选择锥形型线时候应注意不要延长竖井尾部长度.采用模型试验对数值模拟结果进行了验证,两者结果吻合较好,表明该数值模拟方法是可靠的. 相似文献
15.
我国温室产业近年来发展迅猛,由于面积、种植结构与密度等与大田差异较大,沿用大田滴灌系统的设计方法已不适宜,需要根据温室的具体条件确定设计方法。根据我国普通单栋温室情况,通过室内试验研究分析了入口压力、支管长度、毛管间距3个因素对滴灌系统中支管沿程压力分布的影响。结果表明:支管沿程压力分布的均匀性随支管长度的增加、毛管间距和首部压力的减小而降低。结合滴头的水力特性参数得出支管上的最大允许压力偏差为30.85%。毛管间距0.6、0.9和1.2m条件下,满足水力偏差要求的单栋温室支管最大铺设长度分别为20、40和60m。运用量纲分析方法将影响支管水头损失的基本量导出为3个无量纲量υd/ν、υ2/(g d)和L d/s2,通过多元回归建立支管水头损失的经验预测模型(R2=92.4%)。分析了支管能坡曲线的函数形式,回归得到了支管水头损失比和沿程压力分布模型。以上模型预测值与实测数据拟合效果良好,可用于温室滴灌系统水力计算及规划设计。 相似文献
16.
本文不采用缝隙管的假定,提出毛管水头线的多段折线模型;在此基础上,定义了降比r和压比G,根据r的大小,讨论了均匀坡毛管压力水头的分布;讨论了总水头损失计算方法;导出诸水力特征量的计算公式。 相似文献
17.
《灌溉排水学报》2021,(1)
【目的】解决自压微灌管网系统布置与管径优化设计的问题,节省工程投资造价。【方法】以新疆某灌区一微灌工程为研究对象,以微灌系统中各级管道的管段长度、管径为决策变量,支毛管允许水头差、工作压力、管径、流速等为约束条件,以管网总投资最小为目标,分别建立了双向毛管布置和单向毛管布置的自压微灌管网数学模型,并采用混合蛙跳算法进行求解,优化管网的布置及各级管道的管径。【结果】该优化设计方法对自压微灌管网系统能够实现管网系统布置与管径的同步优化,优化设计后的方案干管段数减少,干管每一段的长度和每条支管长度增加,部分管段管径减小,所需总投资为469 129.3元,与依据相关规范和经验进行设计的原方案相比,管网投资降低了21.5%。【结论】该优化设计方法所得的优化结果节省投资明显,混合蛙跳算法收敛性能稳定,计算速度较快,具有较高的计算精度,对水源有保证、地面坡度不大且较为均匀的自压微灌管网系统的优化设计具有一定的应用价值。 相似文献
18.
A new method for calculating total friction head loss in center-pivots with an operational end-gun was developed. The proposed methodology is based on adjusting the previous friction correction factors for center-pivots with end-guns in order to correct their paradoxes and shortcomings. Equations presented in the current work are developed for center-pivots with a finite number of outlets along the lateral and constant outlet spacing and discharge as well as constant discharge and variable spacing. The proposed formulas depend on the number of outlets along the supply pipeline, the exponent of velocity term in the friction formula used and the distance that water is jetted by the end-gun. All equations reduce to the well-established equations for the friction correction factor when the end-gun is turned off. The equations presented here compare well to the stepwise friction calculation method, yet correct slight errors in the way that these friction correction factors were calculated in the past. 相似文献
19.
事故停泵水锤对压力管道的影响 总被引：1，自引：0，他引：1
介绍了大战场泵站的基本情况，对该泵站由于事故停泵水锤造成压力管道破坏的现场进行了调查．基于水锤理论并运用水锤特征线法，建立了事故停泵水锤计算的数学模型，模拟了事故停泵水力过渡过程中的水泵参数及压力变化过程，绘制了该泵站事故停泵的最大、最小水头包络线．通过计算结果及对泵站压力管道破坏情况的分析，得出此次管道破裂是由于事故停泵产生过高水锤压力，沿管线多处出现负压，管道存在质量问题等原因造成．提出的解决方法是更换破坏的管道，同时在管道凸起（3^#镇墩）K0＋075处及（6^#镇墩）K0＋201处设进排气补气阀，防止事故停泵时管道产生过大的负压． 相似文献
20.
混流泵叶轮流动性能数值模拟和叶型优化设计 总被引：5，自引：0，他引：5
在设计工况下,对一个较高比转速的混流泵叶轮内部流动进行三维湍流数值模拟计算.通过分析混流泵叶轮内部的流动特点,发现由于局部结构设计不合理,流道内产生了较大范围漩涡区和壁面脱离现象,增加了流动损失.针对这一问题提出了改进措施,采用一种多参数的优化方法对叶轮叶型进行设计,并分析了叶片型线对叶轮内部流场的作用规律.结果表明,控制叶型弯曲度可以有效控制叶片进口处的马蹄涡,消除近壁面流动分离和漩涡,减小流动中的通道涡强度和影响范围,改进后叶轮流道内存在的涡团和流动脱离现象基本消失,叶轮水力效率相对提高4.74%,单位功耗的扬程增加11.5%.叶轮性能参数的计算数据与试验数据吻合较好,验证了所采用的计算方法及模型的准确性和可靠性. 相似文献