The Research On Hydraulic Transition In Project Of The South-to-North Water Transfer Pipeline System

Beijing Water Supply Project is an important livelihood project improve the security of water supply and water supply in Beijing,which requires a full reliability and high water supply guarantee rate.The main objectives of this project are to achieve joint scheduling of the South-North Water Diversion,Miyun Reservoir and groundwater;to ensure that the main water plants have dual water sources and to reasonably adjust the South-North Water Transfer process and increase the safety of water supply.Beijing loop project has long route and complex structure.There are many water diversion points,multiple surge tanks and three large-scale regulating tank along the route.Considering different water quantity of South-to-North Water Diversion Project,different water supply of water sources and different water consumption of water users in Beijing,there are many possible operation schemes.Water supply conditions in the whole project are complicated.Even to the extent that there will be reverse flow under certain conditions,.In addition,the project operation is very likely change operation due to water supply regulation,maintenance and accident power outage,causing energy imbalance in the system.And due to the inertia of the water body to produce water hammer in the pipeline,resulting in rapid changes in pressure,there may be due to loss of control caused by backflow,pump reversal.This paper focuses on the characteristics of the hydraulic transient process of the loop water supply project under various operating conditions.According to the basic theory of hydrodynamics and the specific characteristics of Beijing loop water supply project,a mathematical model of hydrodynamics for water supply system with multiple water sources is established.And the system static and dynamic simulation are carried out on the different operating conditions of different water resources combination and different engineering risk conditions to check the water pipe network capacity.The hydraulic transient process of the accident and closing process of various operating conditions(forward water supply,reverse water supply)was studied,and the extreme pressure and the setting of surge tank were analyzed.The following main conclusions according to the results of the study:(1)Rational arrangement of air valve can effectively reduce the negative pressure within the pipeline;(2)A variety of measures combined treatment should be taken to avoid water hammer;(3)It is recommended to drive the pump by a frequency converter to avoid water hammer for the pumping stations,which have large water hammer pressure.To weaken the water hammer pressure,power of pump should be gradually reduced.In addition to evaluating the rationality of engineering design,this paper can provide scientific basis for pipeline layout,pump parameter selection,pressure control measures and so on,and lay the foundation for hydraulic system optimization design,system scheduling control design and system safe operation.