| Warping dam is an effective soil and water conservation project,which can not only reduce soil erosion,but also stop mud and silt.It is an important engineering measure to ensure ecological environment in the loess plateau area.However,the vast majority of small and medium-sized warping dams are not equipped with flood discharge facilities,and with the passage of time,the reservoir area is gradually filled up,and it is faced with the risk of dam failure Therefore,the addition of flood discharge facilities has become an urgent problem to ensure the safety of warping dam.In this paper,based on the concept of distributed energy dissipation,three-dimensional numerical simulation and VOF free surface capture technology are used to establish the spillway model scheme with traditional step layout(type 1).In view of the low total energy dissipation rate caused by the insufficient energy dissipation at the front of the stepped spillway in the traditional stepped spillway,a step spillway with front deformed is proposed(type 2).By analyzing and comparing the hydraulic characteristics of the two schemes,the paper puts forward some adaptive suggestions for flood discharge and energy dissipation of three kinds of warping dams of low,middle and high dams in northern Shaanxi.The main research contents and results of this paper are as follows:(1)A stepped spillway with sloping step surface was designed for the front of the step.The experimental study shows that the sloping step surface at the front steps greatly intensifies the water flow,and the strong aerated water flow is formed at the front steps The energy dissipation rate of the sloping step spillway under three low-flow conditions is more than 90%,which is greatly improved compared with the smooth spillway and the traditional step spillway.(2)Through numerical simulation analysis of the flow pattern,velocity,step pressure and energy dissipation characteristics of the two types of shapes under low dam condition,it is concluded that the step main stream and vortex flow exchange a lot of momentum.Type 2 has a higher energy dissipation rate than the type 1,and the maximum energy dissipation rate increases by 14.5%(H=15m,q=4.5m2/s).The maximum negative pressure on the vertical face of type 1 is less than that of type 2.It is suggested that for Fengjiagou No.2 warping dam in northern Shaanxi Province,the single-width discharge q=2.5m2/s,and half of the flow over the dam is long and overflowing,and the layout scheme of type 1 is selected.(3)The hydraulic characteristics of the two types under the middle dam condition are studied.The results show that the energy dissipation rate of the two types under the three conditions reaches more than 60%.The energy dissipation rate of type 2 is improved compared with that of type 1 under various flow conditions,and the maximum energy dissipation rate is increased by 11.2%(H=30m,q=5.5m2/s).Type2 reduces the number of pressure peaks and negative pressure areas on the vertical surface of a single step.For Qiandujiagou warping dam in northern Shaanxi,it is suggested to choose the mode of single-width flow q=5.5m2/s,half of the dam surface overflow,and choose the layout scheme of type 2.(4)The hydraulic characteristics of the two types of shape are analyzed under the condition of high dam.The analysis indicates that the maximum pressure of step horizontal plane of the type 2 is smaller than that of the type 1,and the negative pressure of the step along the path is less,and the pressure peak and negative pressure area of the vertical surface of the step are less.The energy dissipation rate is the best under the two types of small flow conditions,and the maximum energy dissipation rate can reach 90.1%(H=45m,q=2.5m2/s)under various conditions.The maximum energy consumption rate of type 2 was increased by 11.5%compared with type 1(H=30m,q=5.5m2/s).It is suggested that q=5.5m2/s and half of dam surface flow should be selected for Niujiagou warping dam in northern Shaanxi,and the layout scheme of type 2 should be selected. |
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