Abstract
Increasing extreme rainfall events caused by global climate change have had a significant impact on urban drainage systems. As a critical component of a pumping station, a large-scale slanted axial-flow pump (SAFP) featuring high specific speed plays a critical role in mitigating urban flooding and waterlogging. In this study, to reveal the transient characteristics of a SAFP at shut-off conditions, a computational fluid dynamics (CFD) based approach with dynamic mesh was proposed. Multiple shut-off conditions with various shut-down speeds of the sluice gate (SG) were modeled. Our analysis demonstrated that both the shut-off conditions and the slanted structure have conspicuous impacts on the hydrodynamic performance of a SAFP. Reducing the shut-down speed leads to a greater reverse flow rate and higher runner speed. The water hammer effect was simulated with different shut-down speeds, increasing the water head by 5.07–10.42 m, the axial force by 163.46–297.06 kN∙m, and the axial moment by 116.05–224.01 kN∙m. Compared with the axial direction, moments in the radial directions were found with more obvious oscillation as a result of stronger rotor–stator interaction. Due to the gravitational effect of the slanted structure, the fluctuation of the runner in vertical direction presented an off-axis characteristic compared with the horizontal one. As the SG speed increased, pressure fluctuations gradually decreased at various locations across the SAFP.
Highlights
In recent years, global warming has caused a significant increase in extreme weather.The insufficient drainage capacity of urban sewer systems and rapidly increasing water levels often expose cities to the risk of flooding and waterlogging [1–3]
The moment when the rotor reaches a stable state after running for a period under rated working conditions is regarded as 0 s in the transition process, at which the sluice gate (SG) begins to descend, and the rotor is disconnected from the power supply
Based on accurate external characteristic verification with a model pump, the results showed that the SG shut-down speed and the slanted structure had a significant effect on the performance of the slanted axial-flow pump (SAFP)
Summary
Global warming has caused a significant increase in extreme weather. The insufficient drainage capacity of urban sewer systems and rapidly increasing water levels often expose cities to the risk of flooding and waterlogging [1–3]. In order to quickly mitigate the danger of flooding and waterlogging, large-scale pumping stations have been extensively constructed in large cities [4–10]. In urban drainage pump stations, axialflow pumps have been widely used because of their relatively simple structure and good performance with a low head section. Horizontal and slanted axialflow pumps, slanted axial-flow pumps (SAFPs) have been increasingly adopted by urban drainage pump stations, since they are more economical to construct, more convenient to maintain and superior in operation performance, by virtue of their extraordinarily simple and compact structure [11].
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