Although the hydraulic transients in pipe systems are usually simulated by using a one-dimensional （l-D） approach, local three-dimensional （3-D） simulations are necessary because of obvious 3-D flow features in so...Although the hydraulic transients in pipe systems are usually simulated by using a one-dimensional （l-D） approach, local three-dimensional （3-D） simulations are necessary because of obvious 3-D flow features in some local regions of the hydropower systems. This paper combines the 1-D method with a 3-D fluid flow model to simulate the Multi-Dimensional （MD） hydraulic transients in hydropower systems and proposes two methods for modeling the compressible water with the correct wave speed, and two strategies for efficiently coupling the 1-D and 3-D computational domains. The methods are validated by simulating the water hammer waves and the oscillations of the water level in a surge tank, and comparing the results ~with the 1-D solution data. An MD study is conducted for the transient flows in a realistic water conveying system that consists of a draft tube, a tailrace surge tank and a tailrace tunnel. It is shown that the 1-D-3-D coupling approach is an efficient and promising way to simulate the hydraulic transients in the hydropower systems in which the interactions between 1-D hydraulic fluctuations of the pipeline systems and the local 3-D flow patterns should be considered.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
基金the National Natural Science Foundation of China (Grant Nos. 51039005, 50909076)
文摘Although the hydraulic transients in pipe systems are usually simulated by using a one-dimensional （l-D） approach, local three-dimensional （3-D） simulations are necessary because of obvious 3-D flow features in some local regions of the hydropower systems. This paper combines the 1-D method with a 3-D fluid flow model to simulate the Multi-Dimensional （MD） hydraulic transients in hydropower systems and proposes two methods for modeling the compressible water with the correct wave speed, and two strategies for efficiently coupling the 1-D and 3-D computational domains. The methods are validated by simulating the water hammer waves and the oscillations of the water level in a surge tank, and comparing the results ~with the 1-D solution data. An MD study is conducted for the transient flows in a realistic water conveying system that consists of a draft tube, a tailrace surge tank and a tailrace tunnel. It is shown that the 1-D-3-D coupling approach is an efficient and promising way to simulate the hydraulic transients in the hydropower systems in which the interactions between 1-D hydraulic fluctuations of the pipeline systems and the local 3-D flow patterns should be considered.
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.
