Study On Water Level Fluctuation Mechanism And Control Measures Of Large Aqueduct In Middle Route Project Of South To North Water Diversion

China is a country with shortage of water resources and frequent floods and droughts.At the same time,the spatial and temporal distribution of water resources is uneven,showing the phenomenon of more in the South and less in the north.The south to North Water Diversion Project is a major water conservancy project to optimize the spatial and temporal allocation of water resources in China.Since the middle route of the south to North Water Diversion Project was officially put into operation in 2014,it has effectively solved the problem of water shortage in the Huang Huai Hai River Basin in Northern China,greatly improved the ecological environment of cities along the line,promoted the construction of urban ecological civilization,and promoted the green development of social economy.In the Middle Route Project of South to North Water Diversion,large aqueducts need to be built in order to cross the obstacles when the channels intersect with rivers,valleys,depressions and roads.With the normal operation of the Middle Route Project of South to North Water Diversion,the water level of a large aqueduct fluctuates abnormally.The maximum amplitude of fluctuation in the aqueduct is close to 1.0 m.the wave crest strikes the top beam of the aqueduct intermittently.If the wave lasts for a long time,the durability of the aqueduct will be affected and the water conveyance safety of the south to North Water Diversion Project will be affected.This paper studies the fluctuation of large aqueduct in the middle route of South to North Water Diversion Project during the period of large flow water delivery.Firstly,the field measurement of the aqueduct with water level fluctuation in the middle route project is carried out,the water level fluctuation law of the aqueduct is summarized,and the causes of water level fluctuation are analyzed.Secondly,the FLOW-3D fluid calculation software is used,based on RNG k-ε Based on the turbulence model and VOF method,a three-dimensional numerical simulation model of an aqueduct is established.Combined with the field measurement results,the model parameters are calibrated to ensure the accuracy of numerical simulation of aqueduct water level fluctuation in FLOW-3D software.Finally,the water level fluctuation of an aqueduct under different water delivery conditions is numerically simulated by using the established three-dimensional hydraulic calculation model of the aqueduct.By analyzing the vortex distribution behind the tail pier and the amplitude of water level fluctuation in the aqueduct section,the mechanism of water level fluctuation is further studied,the causes of water level fluctuation are preliminarily revealed,and the applicable engineering treatment measures are put forward.The main conclusions are as follows:(1)the Karman vortex street formed at the tail pier of an aqueduct outlet is the source of the abnormal water level fluctuation;(2)By adopting the scheme of lengthening 8 m oval tail pier,the fluctuation amplitude of water level in aqueduct can be reduced to 0.12 m;(3)The water level fluctuation in aqueduct can also be eliminated by arranging two staggered bottom sill at the outlet of the right aqueduct.The fluctuation amplitude of water level in aqueduct can be reduced to 0.15 m when the distance is 7m.The research results can provide theoretical support for the safe operation of the Middle Route Project of South to North Water Diversion,and make the Middle Route Project of South to North Water Diversion give full play to the project benefits on the premise of ensuring the safe operation.