3D simulation of closed sump for hydraulic response in water distribution system: A case study of Longquan pump station in the phase II project of the Central Yunnan Water Diversion Project
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Abstract:
Flow patterns in the closed sump can be very complicated. A sudden start-up or shut-down procedure will drain or flood the closed sump. Longquan pump station belongs to the phase II project of the Central Yunnan Water Diversion Project. The safety and stability of the pumping station operation directly affect the water supply system of the phase II project and further affect the public life and industrial and agricultural production in Kunming. Therefore, it is of great significance to study the closed sump of the pumping station.A three-dimensional (3D) simulation model of closed sump was established by computational fluid dynamics software (Flow-3D) to simulate and analyze the typical hydraulic response of Longquan closed sump. During operation of a pump station, the water level in the closed sump should be within the limit of 5～19.233 m with a stable flow pattern. To ensure the safe operation of the project and verify the rationality of the preliminary design of the closed sump, it is necessary to set up typical working conditions for simulation considering various factors. Four typical working conditions were chosen for analysis, including the sudden start-up and shut-down of the extreme working conditions of the pump. The focus was on whether the sudden drop of water level leads to excessive suction vacuum lift of the pump or whether the sudden surge of water level leads to the top penetration of the closed pump.The simulation results showed that the water level of the closed sump is slightly lower than that of the main canal under design conditions, and the water level difference ranged between 0.003 m to 0.066 m. Under the most unfavorable working conditions, sudden start-up and shut-down of the pump caused the water level to deviate–0.16~+0.10 m according to the designed level. In the water distribution system, the design of the channel-sump connection section affected the flow pattern in the closed sump and the operation efficiency of the pump station. The height setting of the connecting gate chamber and the pump sump must be matched as far as possible to ensure a smooth connection.Based on the analysis following conclusions are made: (1) Because the channel-sump is connected by a short gate chamber, the water level of the closed sump is slightly lower than that of the main channel under design conditions. (2) A sudden start-up and shut-down of the pump caused the water level of the closed sump to drop or surge sharply in a short time. To ensure the super-elevation of closed sump meet the design requirements, the influence of the sudden start-up and shut-down of the pump must be considered in the design. A 1.5 m super-elevation reserved in the preliminary design could meet the requirements of safe operation, which could be used as a reference for other similar engineering designs. (3) In a water distribution system, the closed sump could be used as a surge chamber, which might suppress the water level fluctuation during the hydraulic transition process. Under the most unfavorable working conditions, the sudden drop and surge of the water level could not lead to excessive suction vacuum lift of the pump or the top penetration of the closed pump. Therefore, the preliminary design scheme of this closed sump is feasible. Results of this research can provide technical support for the design and operation of this project, and also provide references for the design and operation scheduling of other similar projects.
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