Study On Transition Process Of Starting And Stopping Of Vertical Shaft Cross-Flow Pump System

In recent years,with the continuous expansion ofChina's urban scale,the standard of urban flood control and drainage has been significantly improved.C hina's riverside and riverside areas are in a gentle terrain.The general pumping stations are low-lift pumping stations.The vertical cross-flow pumping station has the advantage of simple structure,low cost,and convenient installation and maintenance of the motor.It is widely used in urban flood control pumping stations along the Yangtze River and along the river.During the actual operation of the vertical tubular pumping station,there are sone key problems affecting the operation of the pumping station:during the starting process of the vertical tubular pumping device,the starting load will be large,the pumping device will vibrate,and the pump will appear during the shutdown of the vertical tubular pumping device.If the reverse is too fast,the motor will be damaged,which will seriously affect the safe operation of the pump station.Therefore,the research on the start-stop transition process of the vertical tubular pump system has crucial theoretical and practical significance.In this paper,the numerical simulation of the start-stop transition process of the vertical tubular pump unit is carried out.The research contents and results are as follows:(1)In the dynamic numerical simulation of the vertical tubular pumping device,this paper uses the dynamic mesh technology of the three-dimensional numerical simulation software Fluent and the UDF macro program to realize the opening and closing motion of the fest gate during the start-stop process of the vertical tubular pumping station.During the startup process of the vertical tubular pump device,the UDF macro program is programmed to control the pump speed increase process,and the specific UDF macro function is edited during the stop of the vertical cross flow pump device to realize the process of the pump impeller rotation speed changing with the water flow during the shutdown process.(2)In the numerical simulation process of the start-up transition process of the vertical tubular pump device.Through the monitoring of various parameters and performance during the starting process,the influence of punp speed increase time and rapid gate lift time on the starting operation of the vertical tubular pump unit is obtained.During the start of the vertical tubular pump unit:When the pump speed increase time is the same,the shorter the quick gate opening time,the smaller the pump section lift,but the outlet flow rate is initially negative,and the flow path is reflowed.On the contrary,the longer the opening time of the quick gate,the head of the vertical pumping pump,the pump blade torque and the axial torque increase.When the fast gate lifting time is the same,the faster the pump speed is raised,the pump flow rate is increased faster,the pressure difference between the two sides of the pump section is larger,and the pump section has a large lift.On the contrary,the slower the pump speed increase time,the lower the value of the pump parameters is more obvious,the previous water flow backflow is more serbus,and the parameters at the start are fluctuating.Therefore,the pump speed should be increased during the start of the vertical cross-flow pump,and the quick gate simultaneously cooperates with the pump speed to speed up the opening speed.(3)The numerical simulation of the accidental pump stoppage of the vertical cross-flow punp device is carried out,and the nunerical simulation results of the accidental pump-stop transition process of the upstream and downstream water level differences of 0.37m,0.68m,1.0m,1.5m and 2.0m are analyzed to obtain the shaft.Therefore,the relationship between the maximum escape angle velocity and the upstream and downstream water level difference in the transition process of the vertical cross-flow pump device is obtained.In the five different operating conditions studied,the maximum escape angular velocity was 2.0 m in the upstream and downstream water level,and the flying angular velocity was-205.797 rad/s,which was 2.303 times the rated angular velocity.In the process of accidental pump stop,the variation of fluid inside the flow channel under different upstream and downstream water level differences is basically the same,but the maximum escape angular velociy is proportional to the upstream and downstream water level difference.Therefore,the impact of the low water level difference in the vertical cross-flow punp accident stop on the unit is snall,but the high water level difference should be taken as soon as possible to close the gate to prevent the pulp from flying.(4)The numerical simulation of the normal shutdown process of the vertical tubular pumping device is carried out,and the results of the shutdown transition process under the condition that the closing times of different fast gates are 20s and 50s respectively are comared and analyzed.During the normal shutdown process,the axial force of the blade will oscillate,and the oscillation duration is inversely proportional to the fast gate closing time.When the fast gate closing time is 20s,there is no fluid backflow during the shutdown process,but the internal fluid flow on the inlet side of the fest gate is more severe.W hen the fast gate closing time is 50s,the reverse flow phenomenon occurs during the stop process.At 3.8s,the maximum reverse angular velocity of the pump impeller is-12.01 rad/s.At this time,the inlet and outlet flow rates of the vertical cross-flow pump are reversed at the same time.The maximum flow rates were-98.81 L/s and-95.58 L/s respectively.When the shaft cross-flow pump device is shutdown,the fest gate closing time should be shortened according to the actual conditions,the influence of the water flow backflow during the shutdown process should be reduced,and the safety of the unit should be ensured.