Study On 3-D Turbulent Numerical Simulation And Model Experiment For Optimal Design Of Siphon Outlet

Siphon outlet conduits are extensively used in large pumping stations. More than three hundred large pumping stations in China use siphon outlet conduits as cut-off means, which will be adopted in half of more than fifty pumping stations of south-to-north water transfer project of East Route from Changjiang River.An outlet conduit is a transit section between the outlet of guide vanes and discharge basin, the function of which is to make water change flow and diffuse smoothly and recover kinetic energy as much as possible without separation of flow or generation of swirl. Flow patterns in outlet conduits and degrees of recovering kinetic energy determine hydraulic losses of outlet conduits, and obviously affect performance of pump system, especially for low-lift pumping stations, because the magnitude of hydraulic loss takes great amount of total head. So hydraulic performances of outlet conduit have great influence on Pump system. Therefore, it is important to design siphon outlet conduits using scientific method to decrease energy loss and increase efficiency of pumping station, and especially for long annual run-time pumping stations in water transferring projects.One-dimensional flow theory (the average velocity method ) has being used in the hydraulic design of outlet conduits. This theory differs with three-dimensional flow in outlet conduits, so that doesn't meet the needs of higher standards and requirements in large pumping projects, for example, the South-to-North Water Transferring project from Changjiang River, and don't keep up with rapid development of science and technology in the 21st century. With the development of Computational Fluid Dynamics (CFD), it becomes possible to use numerical simulation of three-dimensional turbulent flow in the research and optimization of hydraulic design of outlet conduit.On the basis of numerical simulation theory of three-dimensional turbulent flow,optimization of siphon outlet conduit is conducted according to the hydraulic design requirements, the basic ideas of which is to finish series calculation of flow of different boundary conditions and obtain the optimal hydraulic design. Control equations include Reynolds Navier-Stokes equation and turbulent model. The computation of near-wall flow has been conducted by wall-function. The control equations are discreted by the Finite-Volume-Method. The pressure and velocity fields are coupled with the semi-implicit pressure recorrection algorithm (SIMPLE) based on the staggered grid system. The domain includes siphon outlet conduit and discharge basin and the discretization of domain are conducted on body-fitted coordinates system (BFC). Three-dimensional grids are generated by algebraic method and differential equation method as well as multi-block grid generation technique.The geometry of siphon outlet conduits is quite complex. In order to conveniently design outlet conduit, dynamic numerical model is set up by means of size variables and outline variables.In order to verify the numerical and optimization results, two kinds of siphon outlet conduit models are carried on to observe flow patterns and measure hydraulic losses. Model experiment results indicate that the numerical simulation method to optimize the hydraulic design of siphon outlet conduit is reliable, flow patterns are greatly improved and hydraulic losses are remarkably decreased.