Numerical Simulation And Optimization Research Of The Flow In The Water-Release Structures Of Jiudianxia Hydropower Station

Previously configuration design and hydraulics characteristic of structures of water-release are solved by model testing program. Along with the development of simulation technique, numerical simulation becomes a strongly means to solve this kind of problems gradually. At present, It is important and difficult to trace free surface of flow by numerical simulation, as well as the simulation of water-air flow which pass through the equipment of air entrainment and preventing cavitation. Base on the research result of grand old men, the complicated turbulent overflow in the bi-spillway tunnel in left bank of Jiudianxia Hydropower Station in Gansu Province are simulated using k -εtwo equation model in this paper, as well as the flow of the gate room and escarpment free surface flow of spillway in the right bank.Inlet three dimensional flow of the bi-spillway tunnel in left bank are simulated. Volume of fluid method(VOF)and elastic-lid method are introduced to trace the free surface respectively. The k -εturbulence model is applied to simulate the turbulent overflow and the non-structure grid is used to treat the irregular boundary. Some hydraulics characteristic such as velocity distribution, pressure distribution, free surface and the flux distribute along the flow are obtained. The results indicate that flow of the No.1 and No.2 spillway tunnel are on lateral inflow state in the original design geometry. There is hollow surface in right-hand of weir surface. The flow condition pass through the weir is execrable. Inlet flow can't inpour to the spillway smoothly. Furthermore, biggish negative pressure exists on the spillway crest. At one time, the research also shows that surface traced by Volume of fluid method is exacter than that traced by elastic-lid method while the surface shape is complex.Numerical modeling of the bi-spillway tunnel inlet configuration optimization is implemented in this paper. The results show that the inlet flow condition is improved obviously after setting the guide wall base on original design geometry. Inlet hollow surface disappeared basically. However, biggish negative pressure still exists on the spillway crest. Negative pressure of the spillway crest is disappeared on the whole after modifying the spillway crest configuration base on the intermediate design geometry. Inlet hollow surface also disappeared. The whole configuration has better repellency of cavitation.There exist abruptly enlarge decline bank, conversion from compressive flow to free surface flow and air entrainment. To simulate the flow more accurately, compute areas of the gate room and escarpment free surface flow of spillway in the right bank are divided into many regions. Different types and space grid are built contraposing to each region's configuration and its changes of hydraulics characteristic. Results of the simulation are good.Three dimensional flow of the spillway in the right bank is simulated, especially flow after the abruptly enlarge decline bank of air entrainment. Air entrainment cavum, the altitude and length of water wing, pressure distribution of side wall and the bed, velocity distribution are gained. The results show that value of side wall pressure is on the low side. Negative pressure exists on the midline of the bed. Cavitation numbers along the central line are all under 0.3. Flow strikes the side wall, and obvious water wing are formed. Flow of the original design geometry can't link up smoothly. This result shows that it is easy to produce destroy of cavitation. Some suggestions are put forward for the modification of its shape.Consistency of computed results with the experimental data shows that model in this paper can be applied to the selection design of the inlet shape of structures of water-release.