3-D Numerical Simulation Of Dam-break Flow And Scouring

Dam-break is a sudden and strong destructive catastrophe, which poses a great threat to people and the environment downstream the river. Early researches about dam-break problem are mainly implemented theoretically and experimentally. With the development of the computer and CFD technology, numerical simulations have proven to be an effective mean and has been widely used to study the evolution of dam-break wave.Current simulation about dam-break flow simulation is mainly based on two-dimensional model. However, dam-break flow shows significant three dimensional characteristics on the complex river and the three-dimensional model can reflect the flow evolution process and scour mechanism of dam-break. Research in this paper is based on FLOW-3D to establish three-dimensional numerical model of dam-break with both fixed bed and a mobile bed. In addition, we cited two classic experiment tests,to verify the validity of the model both in hydrodynamic and sediment scouring.The three-dimensional dam-break numerical model is used to simulate flow and scouring in a sudden expansion channel, explore flow phenomenon which is not easy to obtain in experiment. In addition, considering the influence of dam breaking rate and size to dam-break flow and scouring, four conditions are set up. The result shows that the breaking rate has little effect while the size has big effect. And there exits great influence in the dam-break mouth with different size, smaller size turns to greater scouring.The impact of the obstacle is also considered in this study. We set up three sets of tests with different number and layout of obstacles, to analysis acknowledge the flow field and sediment erosion near the obstacle. The result of flow propagation shows that flow field near obstacle is complex with "vortex" shedding. Impact on water surface is greater in the lateral and back side,and impact on flow velocity is greater in the front and back sides. Obstacle spacing also effect on flow velocity distribution, the smaller the spacing is, the larger the influence will be caused. The result of sediment scour shows that the process of dam-break flow meets with obstacles is forming a local scour hole which gradually broaden and deepen. Erosion mainly occurs in the early stage, and then the depth and scope of the scour hole gradually become stable, only some local changes is still happening in this stage and finally it forms a stable bed surface. Scour occurs mainly in the front and sides of obstacle, and the maximum depth position is in the front, then the left and the right. Scour in the side is stronger than in the front at the very start. With the increase of obstacle number and the decrease of their spacing, scour turns to more significant.