Study On Hydraulic Characteristics Of Vortex Shaft Spillway In A Project

The new-builthydropower station in China are mostly located in the canyon areas with high head and large discharge,The demand of the discharge of energy-consuming buildings is higher,vertical vortex spillway is an ideal form of energy dissipation,which not only save the cost of the project,but also apply to the narrow valley,high flow,high drop,complex terrain geological conditions.High energy consumption rate,flexible layout and other characteristics is to play an important role.At present,the technology has been widely used in small and medium-sized hydropower stations,but for the high head and large discharge capacity,the vortex shaft spillway is still in the exploratory stage,There is no practical application for reference,and also less experience.Therefore,it isnecessary to explore the hydraulic characteristics of a high-head(240m)large discharge(1421m3/s)vortex shaft spillway with hydraulic model test.In this paper,The shape of vortex shaft spillway is optimized.Because of the limitation of the traditional model test for the measurement of the complex hydraulic characteristics of silo vortex spillway.the conventional measurement method is difficult to carry out the relevant data.For high water head and large discharge of engineering,shaft internal flow is very complex,Therefore,it is very important to use numerical simulation to simulate the rotation flow of the vortex shaft spillway.The conclusions are as follows:(1)Based on the hydraulic model test of the vortex shaft spillway,the upper section of the shaft and the structure of the vortex chamber are optimized.By adjusting the elliptic curve,The surface of the connection section of the surface of the backwater was significantly weakened,the top of the vortex room to leave enough ventilation space,smooth ventilation on the flat section to meet the operational requirements.The optimization of the section of the shaft and the diversion tunnel is carried out,then we focused on the fluctuating pressure of the shaft bottom in different convergence section.Tests shows:the degree of flow turbulence(2)increase when the area of pressure slope outlet increases,the maximum fluctuating pressure of shaft bottom increases,and the generating conditions of maximum fluctuating pressure also changes.The author analyzes the relationship between the area of orifice and the maximum fluctuating pressure of the shaft bottom,and introduces a concept of unit energy consumption of the water,In water cushion area,the more unit energy consumed,the greater the maximum fluctuating pressure of shaft bottom.We find that it is not reduce the maximum fluctuating pressure of the shaft bottom by deepening the depth of stilling wells,increasing pressure slope length,or changing the number of slope orifice.(2)Comparing the results of the turbulence model with the experimental data of the model,it is found that the trend of cavity diameter,pressure,swirl angle and other parameters which calculated by different turbulence models are basically the same as the model experimental data.but there are some differences in magnitude.Comparatively,the cavity diameter,swirl angle,pressure on base plate of pressing slope and part of shaft wall which calculated by Realizable k-? turbulence model are closer to the experimental measurements on the quantity.Therefore,Realizable k-? turbulence model can be better to simulate the hydraulic characteristic of cavity gyrating flow with super high water-head,high velocity,strong rotary and free surface.(3)Through the calculation results of Realizable k-? turbulence model,The simulated flow pattern features,cavity radius,pressure distribution,free water surface profile,rotational angle and other characteristics of this flow were obtained,The simulation results indicate that the thickness of water layer of rotating flow in shaft is uneven distribution.In the mainstream area,the thickness of the water layer is thicker than that of the Non mainstream.The attenuation gradient of tangential velocity of the rotating flow is gradually reduced from top to bottom,In the upper part of the shaft potential energy,with the decrease of potential energy the axial velocity in the upper part of the shaft increases rapidly.When reaching the middle and lower part of the shaft,The axial velocity of the rotating flow in the mainstream area is still increasing rapidly.but to the Non-mainstream area,the axial velocity of the rotating flow increase slowly.(4)Based on the results of the Realizable k-? turbulence model,by calculating the energy of each section,We found the mechanism of energy dissipation in vertical vortex spillway :the upper part of shaft mainly eliminate the tangential kinetic energy of rotational flow,only accounted for 6.19% of the total energy loss,the middle part of the shaft mainly eliminate the potential energy of rotational flow,accounted for 21.18% of the total energy loss,the lower part mainly use the annular hydraulic jump and water cushion to eliminate most of the residual energy of flow,the energy loss in this part accounts for 58.69% of the total energyloss.