Characterization of startup transition process of a large axial flow pump system with a siphon outlet channel

To investigate the transient process mechanism and the influence characteristics of various factors of a large vertical axial-flow pump system with a siphon outlet channel, transient numerical simulations of the internal flow field were conducted using the volume of fluid method and renormalization group k-ε turbulence model. The simulations accounted for vacuum breaker valve, height differences between the outlet pool water surface and hump bottom of the siphon outlet channel (HDOPH), pump system heads, pump outflow circulations, and pump system startup durations. The results indicate that opening vacuum breaker valve can shorten the startup transition process. The exhaust process can be categorized into the large air bubble exhaust and hump overflow exhaust. When large bubble exhaust is present, HDOPH has a minimal impact on duration, pump head, flow rate, and shaft power of the transition process. The smaller the pump system head, the shorter the transition process duration and the shorter duration of power fluctuations at its high level. The larger the pump outflow circulation, the faster the exhaust in the early stage; however, in the later stage, the larger circulation impedes the exhaust. A longer pump startup duration will prolong the transition process and increase the peak pump head. However, an excessively short startup duration can cause a rise and fall peak in pump flow rate and power during this stage. These results provide a basis for optimizing the design and operation of pumping stations, thereby improving the startup stability and reliability of the pump system.