丁坝冲刷坑的三维水流流态数值模拟

发布时间：2019-04-28 14:02

【摘要】：在各类交通运输方式中，水运具有能耗低、运距长、运量大及利于战备等显著优势，发展前景十分广阔。但是，受自然条件及人为活动影响，我国的航道现状并不理想，普遍存在航道尺度和水流难以满足船舶通航要求这一问题。丁坝作为航道整治的主要建筑物，其作用是：束窄河槽、稳固河岸、调整水流流态以及改变局部河道泥沙冲淤等。据统计，在众多损毁的丁坝中，有相当一部分是由坝头冲刷而导致的，因此对丁坝坝头冲刷坑予以研究有助于探索丁坝损毁的根源。为研究丁坝冲刷坑冲刷，首先需要分析坑内水流结构，本文采用RNGk~ε三维紊流模型模拟丁坝冲刷坑内水流运动，得到以下结论： ①丁坝冲刷坑内的三维水流结构。水流进入冲刷坑时，从丁坝平面上看，水流在冲刷坑内呈现顺时针方向流动，同时会在冲刷坑内形成一些较小的漩涡，这些漩涡的数目、大小及位置根据水流条件的不同而各有差异。此外，受坑内水流作用的影响，冲刷坑壁面处剪切应力大小及分布也不尽相同。 ②水深、流速、冲刷坑深度等因素对坑内水流结构的影响。就水深而言，其在一定范围内增加时会相应增强冲刷坑内的螺旋流和小漩涡，但超过一定深度之后，这种作用反而会减弱。就进口流速而言，其增大会引起冲坑内水流流速和紊动强度的增加。就冲刷坑深度而言，随着深度的增大，冲刷坑内流速和紊动能均随之增大，，一旦超过平衡状态的深度时，流速和紊动能会随之降低。 ③冲刷坑深度公式探讨。从力学角度来看，分析冲刷坑冲刷情况归根结底是比较水流对冲刷坑的剪切应力大小与泥沙临界起动剪切应力大小，如果前者大于后者，泥沙将会起动，冲刷坑被冲刷。通过分析水深和流速对冲坑壁面处的剪切应力的作用，得出坑深和水深比值与弗汝德数的关系，最后借助数模计算结果拟合出两者之间的代数关系式。
[Abstract]:Among all kinds of transportation modes, water transportation has many advantages, such as low energy consumption, long transportation distance, large volume of transportation and benefit to combat readiness, so the development prospect is very broad. However, under the influence of natural conditions and man-made activities, the present situation of the waterway in China is not ideal, and there is a widespread problem that the scale and current of the waterway cannot meet the requirements of the navigation of the ship. As the main structure of channel regulation, the function of spur dam is to narrow the channel, stabilize the river bank, adjust the flow pattern and change the sediment scouring and silting in the local channel, and so on. According to statistics, a considerable part of the damaged groins are caused by the erosion at the head of the dam. Therefore, the study of the scour pit at the end of the dam is helpful to explore the root causes of the damage of the groins. In order to study the scour of groin, first of all, it is necessary to analyze the flow structure in the pit. In this paper, the RNGk~ 蔚 three-dimensional turbulence model is used to simulate the flow movement in the scour pit of the spur dam, and the following conclusions are obtained: 1. When the water flow enters the scour pit, from the plane of the spur dam, the flow of water flows clockwise in the scour pit, and at the same time, there will be some smaller vortices in the scour pit, the number of these vortices. The size and location vary depending on the flow conditions. In addition, the size and distribution of shear stress at the wall of scour pit are different due to the influence of water flow in the pit. (2) the influence of water depth, velocity and scour depth on the structure of water flow in the pit. As far as the depth of water is concerned, the spiral flow and the small vortex in the scour pit will be enhanced when the depth increases within a certain range, but when the depth exceeds a certain depth, the effect will weaken instead. As far as the inlet velocity is concerned, the increase of the flow velocity and turbulence intensity will result in the increase of the flow velocity and turbulence intensity in the scour pit. As far as the depth of scour pit is concerned, the velocity and turbulent kinetic energy in the scour pit increase with the increase of the depth. Once the depth of the equilibrium state is exceeded, the velocity and turbulent kinetic energy of the scour pit will decrease with the increase of the depth of the scour pit. (3) discussion on the formula of scour pit depth. From the point of view of mechanics, the final analysis of scour pit scour is to compare the shear stress of flow to scour pit and the critical initial shear stress of sediment. If the former is larger than the latter, the sediment will start and the scour pit will be scoured. By analyzing the effect of water depth and velocity on the shear stress on the wall of the crater, the relationship between the depth and the ratio of water depth and Froude number is obtained. Finally, the algebraic relation between the two is fitted by the results of numerical simulation.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV863

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