Research On Hydraulic Characteristics And Desilting Effect Of The Flood Discharging And Sediment Long Tunnel

The sedimentation problems of power tunnel have influences on economic benefit of the reservoir.Hydraulic dredging is a primary and effective way to reduce siltation.A newly built long flood discharging and sediment tunnel of a certain reservoir near by the power tunnel was selected as the research object.The hydraulic characteristics of tunnel under different working conditions was studied,including the pressure along tunnel,flow velocity,flow discharge,and cavitation number by a hydraulic model test.And the flow pattern and the scour of the downstream river bed were observed.Through the establishment of a three-dimensional turbulence model,the SST k-Omega turbulence model and the VOF method are used to deal with the free surface.The numerical simulation results are compared with the hydraulic theoretical analysis values and the hydraulic model test values.The rationality of the design of tunnel form was verified.Negative pressure is prone to exist in the gradual transition section of the tunnel,resulting in cavitation damage,which is always a phenomenon in engineering design.Predecessors studied the hydraulic characteristics of area contraction ratio 90%~100% by physical model test.In this paper,through numerical simulation,the effect of changing the outlet area and the length of the gradual change section on the hydraulic characteristics of the gradual change section is studied under different outflow conditions.Plastic sand was taken as the model sand,and the proportion of particle size was matched based on grain size distribution curve.By the sediment model test,the size of the sand funnel was determined,the desilting schemes were compared and selected,the effect “door clean” of power tunnel was obtained,and the reasonable position of the layout of the flood discharging and sediment tunnel was given.Moreover,the research results laid the foundation of this kind of engineering design.The main research work of this paper is as follows:(1)Through hydraulic model tests,the hydraulic characteristics of flood discharge and sediment discharge tunnels under different conditions are studied.The results provide a reference for numerical simulation.Through the numerical simulation method,the SST kOmega turbulence model is used to further study the hydraulic characteristics,and the results are compared with the physical test and theoretical values.The results of model test agree with the results of numerical simulation,and the rationality of the design is verified.(2)The numerical simulation method is used to change the shape of the exit gradient of the outlet of the long tunnel,and the influence of the hydraulic characteristics on the different outflow conditions is also provided,which provides a scientific basis for the engineering design.(3)Through the sediment model test,the sediment discharge scheme is selected and the sand hole is arranged in a reasonable position,which makes the water diversion tunnel reach the effect of the front of the gate,so that the hydropower station is running normally and prolongs the life of the reservoir.