Prototype Observation And Numerical Simulation Of Roughness Coefficient Of Typical Aqueduct In Pumping Irrigation District

My country is a big agricultural country,of which the irrigated area accounts for about 50%of the country’s arable land.Water transportation and distribution in an irrigation area are inseparable from hydraulic structures such as channels,aqueducts,and culverts.Due to the cold and dry climate in northern country,the original concrete-lined channels are vulnerable to frost heave damage,and after a long period of operation,the surface of the channel will fall off,which increases the roughness value of the channel side wall,thereby reducing the over-flow rate.capacity,so that the economic benefits of the irrigation area cannot be fully exerted.In recent years,in order to solve the problem of insufficient flow capacity,for the special tie-rod structure of aqueducts,the flow capacity of domestic channels has been improved from reconstruction and expansion to the use of new materials with reduced roughness.However,at present,the roughness coefficients of new lining materials and channel inner walls are mostly based on experience.This paper summarizes the research progress of SCL anti-seepage membrane and SK scraping-coated polyurea commonly used in domestic water conservancy projects and roughness coefficients.The aqueduct transformed by the lining of the roughening material in the irrigation area is the research object,and the related prototype observation and numerical simulation are carried out in turn.The main research results are as follows:(1)In Hongsibao,Yanhuanding,and Guhai Yangshui irrigation areas,the prototype observation test of roughness coefficient was carried out in Shangmahuanggou,Tongshanggou,Yazawizigou,the Hongjing,keng and Changshantou Aqueduct respectively.According to the constant flow formula,combined with the flow state judgment and different hydraulic gradients and other conditions,the average current roughness ratios of the aqueduct under the condition of constant uniform flow are 0.01287(water surface gradient),0.01426(design gradient),and 0.01459(measured aqueduct bottom).The average roughness of the aqueduct after SCL anti-seepage membrane transformation is 0.01115(hydraulic slope),0.01344(design slope),and 0.01320(measured tank bottom slope);the average roughness of SK scraping polyurea after transformation is respectively It is 0.01060(hydraulic gradient),0.01180(design gradient)and 0.01086(measured groove bottom gradient).Under constant non-uniform flow,the current average roughness of the typical aqueduct in Hongsibao is 0.01324,the average roughness of the SCL impermeable membrane is 0.01179,and the average roughness of the aqueduct after SK scraping and coating polyurea is 0.00974.Regardless of whether it is a constant uniform flow or a non-uniform flow,the two roughening materials can achieve a good roughening effect.(2)The one-dimensional hydraulic modeling was established by HEC-RAS,and the roughness value of the current aqueduct was 0.0131,and the roughness value of the SCL impermeable membrane was 0.0115,and the roughness value of the SK blade-,coated poly urea was 0.0098.Compared with the roughness value calculated by the empirical formula,in practical engineering applications,the roughness coefficient can be determined according to the change of the water surface line,using the constant nonuniform flow formula or the constant uniform flow roughness formula through the inverse calculation of the hydraulic gradient.(3)By comparing the roughness reduction and flow-increasing and construction process of the two kinds of roughening materials,it is concluded that the effect of SK scraping polyurea in reducing roughness and increasing flow is better than that of SCL anti-seepage film.At the same time,its construction is simple and its performance is better than SCL anti-seepage membrane.Therefore,in the future renovation of the aqueduct,SK scraping polyurea can be used for spraying.(4)Deduce the error formula of roughness coefficient measurement under different section forms and different flow states,and carry out error and sensitivity analysis for the calculation of the roughnthe ess coefficient of each aqueduct.The calculation results show that the relative error value of roughness coefficient of each typical aqueduct is less than 20%under the minimum precision level,indicating that the measured results are reliable,and the calculated roughness value can be used in engineering practice.At the same time,whether it is a constant uniform flow or a constant non-uniform flow,the roughness coefficient is highly sensitive to the water depth.Especially under the condition of non-uniform flow,it is most sensitive to the downstream water depth.Therefore,to ensure the calculated roughness value can be used in engineering In fact,in addition to improving the accuracy of current measurement,more attention should be paid to improving the accuracy of water depth measurement,especially downstream water depth measurement,and more precise instruments should be used for measurement.(5)Use Fluent to carry out numerical simulation of water flow in the inlet section of the aqueduct The upstream adopts the velocity inlet condition,and the downstream is free outflow.The finite volume method is used to discretize the control equation.The coupling of velocity and pressure field adopts SIMPLE,RNG model,etc.for the transition section.Three-dimensional numerical simulation of water flow.The simulation results are basically consistent with the measured data,and the research results show that the change of roughness value will affect the water surface line of the channel and reduce the water surface line at the inlet end of the aqueduct The scour is also large,so in the construction design,it can be designed into an arc shape,with a smooth transitional water flow line to reduce the scour strength of the water flow here.