Investigation On Hydraulic Characteristics Of Water Hammer Protection Of Overflow Well In Long-distance Water Transfer Tunnel

The water phenomenon called the water hammer is abrupt alternate changes in the pressure rise and fall that transmit upstream or downstream at a certain velocity and are reflected at the boundary.The pressure changes are caused by the velocity changes due to a sudden shut-off of the valve due,abrupt stop of the pump unit and so on in a pressurized pipeline.Water hammer may produce strong vibration noise in pipe system,may damage pipelines,pumps,valves,and cause pump reversing and pipe network pressure reduction,which does severe harm to long-distance water transfer systems.In the long distance water transfer system,the overflow well setting before the sluice gate can effectively control the fluctuation of the water hammer pressure during the opening and closing of the long distance water transfer system.The method of theoretical analysis and numerical simulation are adopted to analyze the characteristics of water hammer protection in long-distance water transfer tunnel,and to optimize design of shape and parameter of the overflow well before sluice gate.The water hammer calculation model of the long distance water transfer including the overflow well before sluice gate is established to simulate the characteristics of the water hammer in the long distance water transfer tunnel system using the ventilation hole and the overflow well before the sluice gate.The unsteady surge process,the extreme pressure distribution of the whole line under different operating conditions are obtained.The surge characteristics and the extreme pressure distribution of the whole line along the ventilated well with or without pre-gate overflow well are compared,and the water hammer protection effect of the overflow well on the water diversion system is analyzed.In order to optimize the design of the overflow well before the sluice gate,the sensitivities of overflow well height,roughness coefficient,plane position of overflow well,inner diameter of water pipeline,cross-sectional area of overflow well are analyzed.So does the influence of each parameter on the pressure distribution,overflow flow and overflow duration of the whole line.The results of this study show that by setting the overflow well before the sluice gate,it is possible to control the extreme pressure of the water hammer.The height of the overflow well and the inner diameter of the pipeline are the most important factors influencing the overflow process and extreme pressure distribution.Within a certain range,as the height of the overflow well is decreased,the extreme pressure of whole line will decrease correspondingly,but the overflow flow and duration of the overflow well will increase.And as the inner diameter of the water supply pipe is increased,it is not only possible to reduce the extreme pressure distribution of the whole line,but also can reduce the flow of the overflow and duration.In the long-distance tunnel water transfer system,the distribution of the extreme pressure of the whole line can be controlled by increasing the inner diameter of the pipeline and reducing the height of the overflow well.