【作者】 胡君杰；

【导师】 吕宏兴；

【作者基本信息】 西北农林科技大学 ， 农业水土工程， 2008， 硕士

【摘要】 跌水为水利工程中一种较为常见的落差建筑物,特别在我国广大丘陵塬坡地区的渠道输水工程中采用的较为普遍。在修建了跌水的渠道工程中,如果能利用跌水口来精准量水,将可以减少因灌溉系统设置量水设施所产生的水头损失,既可节省大量附加量水设备的建设费用,又可以减少工程量,是一种较为经济、简便的量水方法。因此,研究如何利用跌水口精准量水、确定影响其过水能力的因素以及水流的水力特性,具有重要的应用价值,对保证农田灌溉、发展农业经济起到一定的作用。本文是在梯形渠道上选用矩形跌水缺口形式,采用两种连接渐变段形式——扭面和隔墙,每一种渐变段分别采用四种不同的缺口厚度(δ=0.02m、0.075m、0.13m、0.19m)和四种不同的缺口宽度(bc=0.14m、0.2m、0.25m、0.3m)进行了组合试验,并取得了初步的研究成果。结合理论分析和试验研究,通过建立无量纲数相对临界水深与相对上游水深之间的函数关系,得到了在自由溢流状态下利用跌水口量水的流量公式,由此建立的流量公式满足量纲和谐性,且流量公式简单、测流精度较高。在连接渐变段为扭面时,利用无量纲分析得到的流量公式计算所得流量与实测流量的相对绝对值误差最大为3.615%,最小为2.168%;当连接渐变段为隔墙时,利用无量纲分析得到的流量公式计算所得流量与实测流量的相对绝对值误差最大为4.941%,最小为3.398%。并且得出连接渐变段为扭面时的泄流能力大,测流精度高,为跌水进口段较好的连接形式。通过试验验证分析,发现跌水的流量系数值除了与上游渠道水深、缺口的形式和连接渐变段的形式等因素有关外,还与缺口的厚度有着密切的联系。本文通过建立两无因次数与之间的函数关系,得出在不同条件下流量系数的对数计算公式。并且得出流量系数M随着流量的增大而增大;在相同的流量与相同的缺口厚度情况下,缺口宽度越大,流量系数越小;反之,若缺口宽度越小,则流量系数越大。在同一缺口厚度的情况下,佛汝德数Fr随着缺口宽度的增大而增大;在相同缺口宽度的情况下,缺口的厚度越大,佛汝德数Fr越小;在缺口的厚度和缺口宽度都确定时,佛汝德数Fr随着流量的增加而减小。槽内的佛汝德数Fr除个别点据数值外其余均都小于0.5,基本上可满足利用跌水口来测流的条件。更多还原

【Abstract】 Drop water is one kind of rather common fall structures in the hydraulic engineering, which is used commonly in transport water channel projects for the vast hilly area of the plateau in China, particularly. if we could use the drop water to gauge water accurately, it might not only reduce the loss of head caused by gauging facility of irrigation system, but also might save a lot of additional construction costs for gauging water and also reduce the project quantity, so it is one kind of economical and convenient gauging water method. Therefore, these works, which were how to gauge water by drop water accurately, ascertain the affected factors of discharge capacity and the hydraulic characteristics, has a significant applicative value and plays an important role in field irrigation and agriculture economy development.This article chooses the rectangle gap form of drop water on the trapezoidal channel and uses two kinds of link gradual transition——the distortion and the partition wall, each gradual transition takes four kinds of different gap thickness (δ=0.02m, 0.075m, 0.13m, 0.19m) and widths (bc=0.14m, 0.2m, 0.25m, 0.3m). Preliminary research results are obtained through combination test.Combining theoretical analysis and experimental study, through established two dimensionless number——relative critical water depth hk/bc and the relative upstream water depth H0/bc functional relationships, discharge formula under the free over discharge condition is educed , which has the characteristics of dimensional harmony, simplicity and highly precision. When link gradual transition is the distortion, the maximum absolute error value between calculated discharge by the discharge formula and measured discharge is 3.615%, the minimum is 2.168%; When link gradual transition is partition wall, the maximum is 4.941%, the minimum is 3.398%. In conclusion, gradual transition of the distortion have a big drainage ability, highly measured precision, which is a preferable link form of drop water. Through the experimental confirmation and analysis, we discovered that the discharge coefficient value of drop water has a close relation with the gap thickness, besides the upstream channel water depth, the gap form , link gradual transition form and so on .This article through establish dimensionless numbers between M/ξandδ·bc/H02 functional relationships, obtains discharge coefficient logarithmic computation formula in the dissimilar condition, the results shows that the discharge coefficient increases with the discharge. With the same discharge and gap thickness, the bigger gap width is, the smaller discharge coefficient is, vice versa. With the same gap thickness, the Froud Number Fr becomes larger with the gap width becoming larger. With the same gap width, gap thickness gets bigger when Froud Number Fr gets smaller. Froud Number Fr become larger with the discharge decrease in certain gap thickness and the gap width. Froude number Fr in water slot is less than 0.5 except some individual spots, which basically meet the request of the flow measurement using drop water.更多还原