| High dams in China have the common characteristics of high water head,large discharge,large flood discharge power,narrow valley and complex geological conditions,which make the design of energy dissipation structure of dams extremely difficult.Energy dissipation and scour prevention of water conservancy projects(especially high dams)has always been a hot spot in water conservancy project construction and scientific research.Reasonable energy dissipation measures are the key to determine the safety of discharge structures and even the whole hub.In this paper,a hydropower station in Tibet is taken as the research object,and several key hydraulic problems of combined flood discharge and energy dissipation of surface holes and bottom holes are studied by model test.The main research contents and conclusions of this paper are as follows:(1)The observation test of water flow pattern near the dam area shows that the inflow from the reservoir area is generally smooth when the discharge structure discharges flood,and the water flow pattern near the dam area of the surface holes dam section is normal without adverse flow pattern;When the bottom holes is involved in flood discharge,vortices appear in the corner area between the water inlet and the bottom holes inlet.However,according to the six types of induced vortices on the free surface before the water intake identified by Worcester Alder Laboratory,Massachusetts,USA,the vortex in the corner area will not affect the operation safety of the water inlet of the power station.(2)The hydraulic indicators such as discharge capacity,flow state and water surface lines,pressure characteristic,velocity distribution,energy dissipation effect,flow state,shore velocity and river bed scour are measured.The results show that the hydrodynamics indexes in the surface holes stilling pool are in the controllable range,the energy dissipation effect is good,and the energy dissipation effect of the bottom holes stilling pool is not good.The hydrodynamics index of the bottom holes stilling pool is improved.(3)According to the shape of the tailgate of the stilling basin at the bottom holes and the operation and dispatching mode of flood discharge,a comparative experimental study on energy dissipation and scour prevention is carried out.The results show that the differential bucket type is used at the end of the bottom stilling basin,which is helpful to improve the smooth connection between the water flow from the stilling basin and the downstream water surface,reduce the downstream erosion,and facilitate the sediment discharge of the stilling basin during the sediment discharge operation period;Combined with the characteristics of stilling basin at bottom holes,the reasonable operation modes of bottom holes and bottom holes under different frequency flood conditions are determined..(4)According to the recommended shape of flood discharge and energy dissipation,the bank velocity,riverbed scouring and mound piling conditions on both sides of the downstream river channel were measured under flood discharge conditions of each group,and the optimization scheme and shape were put forward.The downstream guide wall of stilling basin was removed and the scouring particle size was increased,and the sensitivity comparison test of downstream scouring was carried out.The results show that after the guide wall of the downstream stilling basin is removed,the downstream scour hole of the bottom stilling basin moves to the left,which is beneficial to energy dissipation and scour prevention on the right bank;After increasing the scouring particle size,the downstream scouring depth decreases obviously.It provides reference for subsequent engineering design and construction.Figure[48];Table[16];References[84]... |
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