Study On Free-surface-pressurized Flow And Hydraulic Control In The Long-distance Water Diversion System

The hydraulic transients in the long-distance water transfer system, especially the way of channel network coupling pipe network water deliver, caused by hydraulic control is very complex. The hydraulic overhaul, hydraulic accident and discharge regulation etc of project conditions might appear free-surface-pressurized flow, including separation phenomenon in the gate-closing process, water-filling or water-releasing after hydraulic overhaul, the water touch the crest of free-flow conduit during accident power off. The pressure pipe may encounter water impact pressure and lead to breakage under the state of free-surface-pressurized flow.The way of stepped low-pressurized water delivery has successfully been used in the project of Kunming Zhangjiuhe River water diversion and it was adopted by Tianjin Main Line of South-to-North water transfer project recently. Except lots of benefits, however, there is much concern about that it complicates the phenomenon of unsteady flow which evoked by hydraulic control, especially on the asymmetric water transfer, which one or more lines of whole line stop,begin delivering water, at operation. During the run of asymmetric water transfer, it will not only cause seriously hydraulic oscillation, but also influence other lines'operation. A mathematic model of asymmetric water transfer was built based on the method of characteristics, the paper analyses the operation of changing lines, discusses the way of continuous opening,closing gate and optimizes the time interval between two gates'operation.The water-filling operation frequently took place in pressure conduit for overhaul etc. But it always adopted appropriate discharge according to experience which was formed in practice, the hydraulic transient phenomenon still unknown for us by far. So, a mathematical model of water-filling was established with Preissmann implicit difference method, it can simulate flow movement from anhydrous state to pressure flow in conduit, including the free-surface-pressure flow. Finally, the model was applied to numerical calculation of Tianjin main line of South-to-North Water Transfer Project. Finally, the paper discussed the disadvantageous phenomenon and elicited a secure, economic operation mode. The result shows that the water-filling model achieved a satisfied precision.