Study On Water Hammer Protection For Long Distance Negative Head Pipeline Water Transfer Project

Building long-distance water transfer projects is an effective way to effectively solve the uneven distribution of water resources in China and achieve rational allocation of water resources.Transportation of high water level water resources to low water level areas through pressure pipelines is a common form of long-distance water transfer.During the operation of the water transfer system,pipeline water hammer will greatly threaten the safety of the water transfer system,causing significant losses.Therefore,conducting research on transient characteristics and safety protection measures of long-distance negative lift pipeline water delivery systems have important practical significance to ensure the safe,stable,and efficient operation of water supply pipelines.Aiming at the common problems of valve closing and pump stopping water hammer in long-distance negative head water transfer projects,how to set up water hammer protection facilities,provide reasonable water hammer protection schemes,and control the positive and negative pressure of water hammer within the pressure bearing range of the pipeline is the key to water hammer protection in water transfer projects.This paper uses a research method that combines theoretical derivation and numerical simulation to conduct in-depth research on the protection of valve closing water hammer and pump stopping water hammer in long-distance negative head water regulation systems,and proposes optimized protection schemes for valve closing water hammer and pump stopping water hammer,and further explores the impact of air valve intake and exhaust flow characteristics on the protection effect of water hammer.Provide design basis for water hammer protection for similar long-distance negative lift pressure pipeline water transmission projects,and provide reference for ensuring the safe operation of the project.The main research contents and conclusions of the paper include:(1)Taking a long-distance gravity flow water conveyance project as the research object,the hydraulic transient characteristics of the project were analyzed,and an optimized scheme for water hammer protection of the combined valve group for valve closing was proposed.At the same time,the impact of the installation position of the intermediate online valve and the valve closing law on the protection effect was explored.Conclusion: The combined valve group water hammer protection scheme consisting of an intermediate online valve and an end valve can effectively control the water hammer of pipeline valve closing.(2)Based on a negative lift pressurized water conveyance project,according to the water hammer protection characteristics of the water hammer air valve,combined with the layout and pressure of the pipeline,the water hammer protection scheme of the project is designed,and the impact of the air valve and the air valve surge chamber on the hydraulic transition process of the water conveyance system of the long-distance pressurized pumping station is analyzed.It is believed that the protective scheme combining air valve and air valve surge chamber can effectively suppress the negative pressure of water hammer and control the water hammer when the pipeline stops pumping.(3)Based on the DN100 waterproof hammer air valve,a three-dimensional calculation model of the air valve was established.The intake and exhaust characteristics and flow field characteristics of the waterproof hammer air valve were simulated and analyzed,and the impact of the intake and exhaust characteristics of the air valve on water hammer protection was explored.The limitations of the water hammer protection effect of a single air valve are further verified,and a conclusion is drawn that the relevant parameters of the intake and exhaust flow characteristics of the air valve are dynamically changing during operation.