Investigation On Numerical Simulation And Optimization Of Bu-type Bifurcated Pipe

With the wild construction of storage power stations in the world,pressure pipes,as an important part of water-discharge system in hydropower station,have experienced a huge development in terms of its design theory,calculation method and construction technology.The bifurcated pipe in pressure pipe system has aroused widespread attention due to its complicated and large head loss,the research on hydraulic characteristics of bifurcated pipe is very significant.For a Y-type pipe with large diameter-difference,backflow,reflux and negative pressure commonly arise in the connection,which may bring a threat to the pipeline safety.Hydraulic model test and a three dimensional CFD numerical model was established.The velocity,pressure distributions and flow characteristics were obtained.Compared with model test,numerical simulation can clearly reflect flow regime variation and match well with model test.On the basis of verification of the accuracy of the numerical simulation,the connection method of the Y-type pipe was optimized.The calculation model of cylindrical direct transition and taper transition were established,and the flowing state with or without taper transition under different operating conditions were compared.The result shows that the taper transition can efficiently eliminate the negative pressure of bifurcated pipe,and reduce the back-flow scale around the Y-type pipe interface.It plays an important role in the prevention of cavitation damage in the Y-type pipe and the improvement of flowing state,which provides a reference for the optimization of the bifurcated pipe.Moreover,the mechanism of different head losses were investigated in this study,and the effects of different split ratios and branch angles on the head loss coefficient were also discussed.By calculation and analysis,the split ratio plays a significant role on the water head loss,when the split ratio is about 0.22,the average cross-sectional velocity of the main pipe and branch is nearly equal,the water head loss of branch pipe is minimum.The degree of branch is 45°-60°,the flow state of the bifurcation tube is better,and the local water head loss coefficient is minimal.