Experiment And Numerical Simulation Of "S" Style Spillway

The axial line of spillway is straight in great majority of hydraulic works. But because of some factors, such as geological conditions, characteristics of works, construction conditions and economic indicator etc., the bent spillway has to be built in a few works. Bent spillway is rare at present, model tests on it are insufficient, and the 3D numerical simulation of bent spillway has not been reported yet. Xiaonanhai reservoir spillway contains two curved conduits, presenting rarely 'S'style on the plane surface. The centrifugal force and the steep slope make transverse superelevation notable, and the rhombus wave is formed to make the flow turbulence tempestuous; Because there are double curved conduits, the water level of left bank is lower than that of right bank at the outlet of upstream bend, but when the flow arrives at the inlet of downstream bend, the water level of left bank is higher than that of right bank reversely, and the tangential path between of two curved ways is short, which makes transverse superelevation superposition of downstream bend great. In order to improve the flow pattern to meet the need of pratical project, 'S'type spillway is studied by model test and 3D numerical simulation combining the Xiaonanhai reservoir spillway in this paper, and the main contents and conclusions are as follow: (1) According to the results of theoretical calculations and model tests, though the lateral difference in elevation of bottom is as high as 4.0m, spillway's flow pattern can't meet the need of the project. So slopping sills are applied to this project. By modifying height and angle of the slopping sill for many times, an effective scheme is adopted to this project. (2) In the experiments, the water surface curve at left and right bank of chute, the velocity of cross-section and the superelevation are obtained when the flood frenquency are 3.33%, 1%, and 0.1%. The data after arranging slopping sills is compared with data before arranging slopping sills. (3) 3D numerical simulation can eliminate scale effect by applying the data on prototype, get entire data of the flow field, and alter the parameter easily. In this paper, The RNG k-εtwo-equation turbulence model and VOF methods are used to simulate three dimensional turbulent flow of 'S'style spillway. The characteristics of spillway in different work conditions mentioned above are obtained. (4) The simulated results depend considerably on the mesh. In this paper, the body-fitted coordinate method is applied to discrete the simulation domain, and different meshes are plotted in different work condition. The mesh lines are generated generally according to the direction of flows. The simulation domain is divided into several regions in this paper. The different meshing methods are employed to different regions. The meshes of key regions, such as curved conduits and the hydropneumatic interfaces are dense, while the meshes of secondary regions are sparse. The unstructured grids are applied to plot the difficult regions, such as the bottom of curved conduits, while structured grids are applied to plot the simple regions. Moreover, grid adaption method is applied to refine the mesh of near-wall regions. Above methods of meshing improve the speed and precision of the simulation. (5) The simulation results are compared with the experimental data, the free water surface along the spillway and the velocity of two methods are in good agreement, which indicates that by arranging slopping sills at the bottom of the curved conduits, the lateral distribution of the flow is improved, the back flow in stilling basinis eliminated, and the dissipated energy ratio is increased. The flow pattern of optimized spillway is in good condition, which can meet the need of flood discharge and energy dissipation.