Abstract
In order to explore the transient characteristics of the large-scale vertical siphon axial flow pumping station during the start-up and exhaust process, numerical simulations were carried out on the start-up process of the axial flow pumping station under the two starting modes of pre-opening the vacuum breaking valve and keeping the vacuum breaking valve closed. The calculation results show that during the start-up phase of the unit, the flow separation phenomenon of the impeller channel of the pump device with the vacuum breaking valve closed is serious, the large-scale vortex in the guide vane blocks the flow channel, and the instantaneous impact on the blade surface is strong. The flow field of the pump device with pre-open vacuum failure valve is obviously less affected by the instantaneous impact characteristics during the start-up of the pump. The range of high entropy production area in the impeller channel is reduced, the duration of high entropy production area is significantly shortened, and the instantaneous impact on the blade surface is weak. Under the two starting modes, the internal flow field of the pump device is similar in the evolutionary law. The unstable flow phenomenon of the pump device is most prominent in the weir flow stage. The maximum instantaneous impact on the blade surface also mainly occurs in the weir flow stage. A very small part of the remaining gas in the siphon formation stage is difficult to discharge and takes a long time. After the pump device is exhausted and enters a stable operation state, the external characteristic parameters are in good agreement with the test results. Compared with the starting method in which the vacuum breaking valve is kept closed, the method of pre-opening the vacuum breaking valve reduces the maximum starting head by 20% and the exhaust time by 43%. The pre-open vacuum breaking valve effectively avoids the system instability caused by the start-up and exhaust of the pump device.
Highlights
Pumping stations are widely used in urban drainage, inter-basin water transfer and agricultural irrigation (Wang et al, 2010; Xie et al, 2018; Intriago Zambrano et al, 2019)
In order to explore the transient characteristics of the vertical pump system in the start-up and exhaust process, this paper conducts a numerical simulation study on the start-up transition process of the vertical axial flow pump system based on the commercial fluid calculation software ANSYS CFX
In order to explore the transient characteristics of the start-up and exhaust process of the vertical siphon axial flow pump unit, this paper conducts a numerical simulation study on the whole system of the pumping station
Summary
Pumping stations are widely used in urban drainage, inter-basin water transfer and agricultural irrigation (Wang et al, 2010; Xie et al, 2018; Intriago Zambrano et al, 2019). Zhang et al (2020) studied the transient hydraulic performance of self-priming clear water pump under fast and slow start-up conditions They found that the similarity law of the pump is not suitable for the first half of the startup process when the steady-state flow is small, nor for the second half of the startup process when the steady-state flow is large. There are few studies on the startup and exhaust transient characteristics of vertical axial flow pump system with siphon outlet channel. In order to explore the transient characteristics of the vertical pump system in the start-up and exhaust process, this paper conducts a numerical simulation study on the start-up transition process of the vertical axial flow pump system based on the commercial fluid calculation software ANSYS CFX. In order to monitor the pressure change at the top of the hump of the outlet flow channel, a monitoring point is set at the top of the hump
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