When using the draft-tube vacuum to be less than 8.0 m as the rule to set atailrace surge tank, a mixing function that describes the process of water-hammer vacuum andvelocity-head vacuum varied with time is proposed,...When using the draft-tube vacuum to be less than 8.0 m as the rule to set atailrace surge tank, a mixing function that describes the process of water-hammer vacuum andvelocity-head vacuum varied with time is proposed, on the assumption that the guide vane of thehydraulic turbine and the turbine discharge were all changed linearly. An exact maximum of thedraft-tube vacuum for the first-phase water-hammer and the last-phase water-hammer is obtained.Finally a much more reasonable formula of critical tailrace length is derived. The results of twocases show that the formula proposed can determine correctly and reasonably whether a tail-racesurge tank is needed or not, and are more suitable for project design than the formula suggested bythe specification.展开更多
The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threat...The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threaten the station＇s safe operation. It is necessary to investigate the transient mechanisms in the tailrace system with vent tube. In this paper, a 3-D, two-phase numerical model of a vent tube on the connection of the tailrace tunnel and the diversion tunnel, is developed based on the FLUENT with the volume of fluid（VOF） algorithm to investigate the transient air-water flow patterns and the complex hydraulic phenomena in the vent tube of the tailrace system. A 1-D and 3-D unidirectional adjacent coupling（1-D-3-D-UAC） approach with a linear interpolation method is adopted to adjust the timesteps between the 1-D model and the 3-D model on the tunnel inlet and outlet boundaries through the user defined function（UDF）, to transmit the data from the 1-D model to the 3-D model. The model is verified by comparing the results obtained by using the 1-D model alone and from the experiments in literature. The transient flow processes under the full load rejection consist of four stages： the water level dropping stage, the air entering stage, the air pocket collapsing stage, and the air exiting stage. Detailed hydraulic phenomena in the air pocket collapsing process are also discussed.展开更多
To date,the Three Gorges Project is the largest hydro junction in the world.It is the key project for the integrated water resource management and development of the Changjiang River.The technology of the project,with...To date,the Three Gorges Project is the largest hydro junction in the world.It is the key project for the integrated water resource management and development of the Changjiang River.The technology of the project,with its huge scale and comprehensive benefits,is extremely complicated,and the design difficulty is greater than that of any other hydro project in the world.A series of new design theories and methods have been proposed and applied in the design and research process.Many key technological problems regarding hydraulic structures have been overcome,such as a gravity dam with multi-layer large discharge orifices,a hydropower station of giant generating units,and a giant continual multi-step ship lock with a high water head.展开更多
文摘When using the draft-tube vacuum to be less than 8.0 m as the rule to set atailrace surge tank, a mixing function that describes the process of water-hammer vacuum andvelocity-head vacuum varied with time is proposed, on the assumption that the guide vane of thehydraulic turbine and the turbine discharge were all changed linearly. An exact maximum of thedraft-tube vacuum for the first-phase water-hammer and the last-phase water-hammer is obtained.Finally a much more reasonable formula of critical tailrace length is derived. The results of twocases show that the formula proposed can determine correctly and reasonably whether a tail-racesurge tank is needed or not, and are more suitable for project design than the formula suggested bythe specification.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFC0401810)the Research Project of Science and Technology Commission of Shanghai Munici-pality(Grant No.16DZ1202205)and the Fundamental Research Funds for the Central Universities(Grant No.2016B10814)
文摘The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threaten the station＇s safe operation. It is necessary to investigate the transient mechanisms in the tailrace system with vent tube. In this paper, a 3-D, two-phase numerical model of a vent tube on the connection of the tailrace tunnel and the diversion tunnel, is developed based on the FLUENT with the volume of fluid（VOF） algorithm to investigate the transient air-water flow patterns and the complex hydraulic phenomena in the vent tube of the tailrace system. A 1-D and 3-D unidirectional adjacent coupling（1-D-3-D-UAC） approach with a linear interpolation method is adopted to adjust the timesteps between the 1-D model and the 3-D model on the tunnel inlet and outlet boundaries through the user defined function（UDF）, to transmit the data from the 1-D model to the 3-D model. The model is verified by comparing the results obtained by using the 1-D model alone and from the experiments in literature. The transient flow processes under the full load rejection consist of four stages： the water level dropping stage, the air entering stage, the air pocket collapsing stage, and the air exiting stage. Detailed hydraulic phenomena in the air pocket collapsing process are also discussed.
文摘To date,the Three Gorges Project is the largest hydro junction in the world.It is the key project for the integrated water resource management and development of the Changjiang River.The technology of the project,with its huge scale and comprehensive benefits,is extremely complicated,and the design difficulty is greater than that of any other hydro project in the world.A series of new design theories and methods have been proposed and applied in the design and research process.Many key technological problems regarding hydraulic structures have been overcome,such as a gravity dam with multi-layer large discharge orifices,a hydropower station of giant generating units,and a giant continual multi-step ship lock with a high water head.
