Study On The Characteristics Of Hydraulic Transition Process Of Axial Flow Pump Station With Siphon Outlet Channel

Siphon outlet conduit is widely used in large-scale axial-flow flood control and drainage pumping stations in our country because of its convenient and reliable cut-off mode.However,with the change of hydrogeological conditions,the situation of water level exceeding the hump often occurs in flood season.Under the condition of water level exceeding the hump,the siphon outlet conduit can not be cut off,which directly affects the safe and stable operation of the unit.Therefore,aiming at the hydraulic stability of the startup and shutdown of an axial-flow pump station with siphon outlet conduit under the condition of Super-Hump in Guangdong Province,the start-up and shutdown characteristics of the axial-flow pump under the condition of Super-Hump are analyzed based on the theory of transient flow,and a combined control strategy of pump and gate under the condition of Super-Hump is proposed to determine the operation scheme of the gate under the condition of super-hump,which has strong application value and learning.The value of surgery.The details are as follows:Aiming at the start-up problem of axial flow pump under Super-Hump conditions,considering the law of air pressure variation at the hump of flow channel,the start-up transition process was simulated by step-by-step superposition method.The results show that the maximum start-up head occurs at the same time as the rated speed of the unit.The acceleration of gate opening time is helpful for the unit to enter stable operation as soon as possible.The scheme of "30% pre-opening of fast gate,120 s linear opening of gate and 6 s starting of pump" can meet the start-up requirements under the condition of Super-Hump less than 2 m.Aiming at the problem of normal shutdown of axial flow pump under super hump condition,the transient flow theory is used to calculate the transition process based on the full characteristics of the pump and the boundary conditions at the outlet gate end of the channel.The results show that the maximum reversal speed will exceed 1.2 times of the rated speed when the pump stops normally without closing a certain gate opening in advance,which will threaten the safety of the pumping station.When the pre-closing opening of the gate exceeds 50%,a large negative pressure will occur.It is suggested that the gate should be closed 30% in advance and the gate should be closed linearly in 100 s when the pump stops normally.Aiming at the protection of axial flow pump from accident shutdown under super hump condition,based on the basic theory of transient flow,an optimization model of two-stage closure law of gate is established,and the chaotic particle swarm optimization algorithm is used to solve the problem.The results show that the chaotic particle swarm optimization algorithm has strong optimization ability and good stability,which effectively improves the protection effect of two-stage valve closing water hammer;the results of multiple optimization reveal that in the two-stage valve closing,the first-stage valve closing speed and angle play a stronger role in weakening the water hammer;when the maximum ultrahump water level is less than 2 m,the strategy of "14 s fast closing stroke 66%,104 s slow closing stroke 34%" is adopted.It can effectively protect the water hammer from accident.