Experimental analysis of forebay of Xihe pumping station under asymmetric operation
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Abstract:
The forebay is a structure connecting the suction sump (inlet passage) and the diversion channel (igniting river) of the pumping station, and its flow pattern has a direct impact on the safe and stable operation of the pumping station unit. The drainage flow and diversion flow of Xihe pumping station in Zhongshan City, Guangdong Province, are both very large, and the diversion condition is lateral inflow. Higher requirements are now set forward for the flow conditions of the forebay of the pumping station. If the incoming flow of the forebay is not uniform, there will be adverse flow patterns such as bias flow, deflected flow, backflow, and air-core vortex, which will adversely affect the safe operation of the Xihe pumping station and the operating efficiency of the unit.In order to clarify the flow pattern characteristics of the forebay of Xihe pumping station during the operation of asymmetric units, taken the Xihe pumping station project as the research object, the physical model test method was used to carry out the overall physical model test of the forebay and inlet passage of the pumping station during different startup combinations. The computational fluid dynamic technology was used to numerically analyze the operation scheme of eight units fully open at the lowest water level.It was found that, when the eight units of the Xihe pumping station are fully opened for drainage, the mainstream is centered in the inland river diversion section. The surface velocity in the mainstream zone is mostly in the range of 0.9 m/s to 1.2 m/s and the surface velocity in front of the inlet of the pumping station is in the range of 0 to 0.6 m/s. In the outlet sump and the outer river section of the pumping station, the surface velocity in the mainstream zone is mostly in the range of 0.9 m/s to 1.2 m/s, and the maximum velocity is 1.44 m/s. The flow pattern of the upstream and downstream diversion sections of the pumping station is relatively smooth. The water surface fluctuation at the inlet of the pumping station is small, and the water flow is relatively stable and smooth. Under the asymmetric unit operation scheme 2, the surface velocity in the mainstream zone of the inland river diversion section is mostly in the range of 0.6 m/s to1.0 m/s and the surface velocity in front of the inlet of the pumping station is in the range of 0 to 0.4 m/s. In the outlet sump and the outer river section of the pumping station, the surface velocity in the mainstream zone is mostly in the range of 0.6 m/s to 1.0 m/s, and the maximum velocity is 1.32 m/s. Affected by the non-startup of the number 1 and number 8 units, the flow velocity at the middle bottom is greater than that on both sides, and a weak recirculation zone is formed at the inlet of the non-startup unit, but there is no harmful surface vortex. Under start-up scheme 3, the surface velocity in the mainstream zone of the inland river diversion section is mostly in the range of 0.6 m/s to 1.0 m/s and the surface velocity in front of the inlet of the pumping station is in the range of 0 to 0.4 m/s. In the outlet sump and the outer river section of the pumping station, the surface velocity in the mainstream zone is mostly in the range of 0.6 m/s to 1.0 m/s, and the maximum velocity is 1.47 m/s. The bottom velocity distribution of the upstream section of the pumping station is more uniform along the section, and the bottom velocity distribution of the downstream section of the pumping station is also affected by the non-startup pump, with the bottom velocity in the range of 0.35 m/s to 0.81 m/s and 0.42 m/s to 0.61 m/s, respectively. Under start-up scheme 4, whose flow pattern of the forebay is stable and the uniformity of the bottom velocity distribution of the inlet section is 77.2%, the flow field distribution of the inlet and outlet surfaces of the pumping station is similar to that of start-up scheme 3. Under the conditions of full load drainage flow and the lowest water level, the difference in velocity distribution on both sides of the pier of the inlet passage of the side unit is more significant, and the difference in velocity distribution of the middle unit is smaller. There are some differences in the axial velocity distribution uniformity and velocity weighted average angle on both sides of the pier of the inlet passage of the intermediate unit and the side unit. Therefore, the safety and stability of the operation of the side unit should be paid attention to when the unit is fully opened.The followings are the results: (1) When the eight units of Xihe pumping station are fully opened for full load drainage and the lowest water level, the surface velocity in front of the inlet of the pumping station is small. The water surface fluctuation at the inlet of the pumping station is small and the water surface fluctuation at the outlet of the pumping station is slightly larger. The average uniformity of the axial velocity distribution in the inlet passage of eight units is 74.31%, and the average value of the velocity weighted average angle is 81.18°. The hydraulic performance index of the inlet surface of the inlet passage of the units on both sides is the lowest, and the stability and energy consumption of the operation are the largest. (2) At 75% of drainage load, the startup schemes of three different units were analyzed by a physical model. Under start-up scheme 3, the inlet flow pattern of the pumping station was stable. There was no obvious swirling flow, and the uniformity of velocity distribution at the bottom of the inlet section was 78.2 %, which was higher than that of startup scheme 2 and startup scheme 4. Startup scheme 3 was recommended at 75% of the drainage load. The research results can provide a certain reference value for the actual operation and management of Xihe pumping station.
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