Experimental Study For Drop Water Gauging In The Trapezoidal Channel

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.