Research On The Operation Process Of Long Distance Water Transfer Open Channel Regulation And Storage System In Multi Stage Pump Stations

With the rapid development of China’s social economy and the advancement of urbanization,the demand for water resources in industries,agriculture,and daily life is also increasing day by day.The contradiction between water resource demand and supply is becoming increasingly acute.This characteristic is particularly evident in the water scarce areas of northwest China.The most direct and effective way to solve the contradiction between supply and demand of water resources in the northwest region is to transport water from resource rich areas to resource scarce areas,which is a cascade pumping station project for cross basin water transfer.This type of project has the characteristics of long distance,high lift,and large flow.In practical engineering,it is inevitable for the cascade pumping station system to experience accidents such as canal collapse,tripping and shutdown due to overload,large flow,and high water level operation.As a result,the water delivery system enters the hydraulic transition state from a constant flow state,which has a significant impact on the overall energy consumption of the entire project,causing serious waste of hydropower resources and secondary disasters.In order to ensure the safe operation of the cascade pumping station project,this paper takes the multi-stage water conveyance system of Jingdian Phase II in Gansu Province as the research object,and uses the methods of numerical simulation,theoretical analysis and field investigation to carry out the research on the hydraulic transition process of the open channel under the control of the regulation and storage system after the pump station stops in an accident,the change characteristics of the regulation and storage process of the cascade pumping station water conveyance system,and the coupling process of the water conveyance flow of the open channel and the water return flow of the regulation and storage tank,The main conclusions are as follows:(1)After the pump station is shut down,there is a hydraulic oscillation phenomenon of alternating rise and fall of the water level.The peak value of the water level in the inlet forebay is the height of the first surge wave generated in the forebay.Over time,the peak value of the water level oscillation shows a gradually decreasing trend.The time when overflow occurs on the overflow weir is mainly during the first water level oscillation process.By analyzing the changes in water levels along the open channels of each pumping station,the backtracking distance of backwater waves in the open channels of each pumping station is obtained.After the pump station is shut down,the flow velocity in the channei is divided into three areas based on the cross-section: the section area where the falling water wave reaches along the flow direction,the section area where the backwater wave reaches,and the relatively stationary area.The flow velocity from large to small is the falling water wave area > the backwater wave area >the relatively stationary area.(2)The calculation method for the volume of the storage tank after the pump station is shut down is established,and the layout principle of the storage tank is proposed.In view of the difference between the theoretical calculation and numerical simulation of the volume of the storage tank,the correction coefficient of 0.84 for the volume expression of the storage tank is proposed through positive proportion function fitting,and the theoretical expression for the volume of the storage tank after the pump station is shut down is summarized,which provides a theoretical basis for the establishment of the storage system for the cascade pump station project.In view of the overflow of the channel under the condition of emergency shutdown,three safe regulation and storage modes are proposed: the regulation and storage mode of the regulation and storage tank,the heightening regulation and storage mode of the water conveyance channel,and the heightening joint regulation and storage mode of the regulation and storage tank and the water conveyance channel.(3)The specific impact range of water transfer in the storage tank at different coupling angles is within the water flow coupling intersection area.When the coupling angle is 60 °,the water level at the coupling intersection of the channel drops to the lowest value,and the distribution of flow velocity in the channel is the most uneven.It is recommended to have a coupling angle of90 ° between the water conveyance in the storage tank and the channel.