桥墩局部冲刷坑发展中的三维紊流场研究

发布时间：2018-04-20 23:31

本文选题：圆柱型桥墩 + 局部冲刷　；参考：《北京交通大学》2014年硕士论文

【摘要】：桥梁墩台局部冲刷是导致跨江桥梁破坏的主要原因之一,局部冲刷深度与冲刷坑形态的正确预测,是桥梁合理设计与安全运营的重要保障。由于墩周局部冲刷坑内水流结构复杂,泥沙输运理论不完善以及坑内泥沙随机崩塌等问题,现有水沙耦合计算模型不能准确地模拟出局部冲刷坑的演变过程,故本文通过实验室试验和数值计算研究了圆柱型桥墩周围局部冲刷过程中墩周水流的变化,主要工作如下： (1)介绍了国内外因桥墩台局部冲刷而发生的桥梁水毁事件,结合局部冲刷的研究现状,论述了局部冲刷发展过程中墩周流场变化对局部冲刷机理研究的重要性。 (2)基于计算流体力学原理,应用Fluent中的RNGk-ε湍流模型,经适当的壁面处理,对圆柱型桥墩局部冲刷发展过程中复杂的三维流场进行了数值模拟。 (3)通过平床条件下试验测量得到的墩周流速对数值模型结果准确性进行了验证,两者结果的一致性证明了本文方法的有效性。同时,本文对平床条件下墩周复杂的水流进行了分析,其中数值模拟能很好地模拟出墩周的水流结构。 (4)以实测圆柱型桥墩冲刷过程中不同时刻下的冲刷坑形态为边界条件建立相应数值模型,其模拟结果揭示了墩周水流流速、床面切应力、涡量和紊动能随冲刷过程的变化规律。 (5)根据局部冲刷试验与不同时刻下墩周水流紊流场的分布情况,分析结果表明了墩周马蹄涡系,加速水流及尾涡是引起局部冲刷的主要动力因素。在冲刷初期,墩侧加速水流对桥墩局部冲刷起主导作用；随着冲刷的发展,马蹄涡系对冲刷的影响作用增大,与墩侧加速水流作用相当；而墩后水流一直都处于尾涡回流区,流速较小,但其紊动性较强,墩后床面泥沙冲刷主要受到尾涡和水流紊动的共同作用。
[Abstract]:The local scour of bridge pier and abutment is one of the main reasons leading to the destruction of bridge across the river. The correct prediction of local scour depth and scour pit form is an important guarantee for the rational design and safe operation of bridge. Due to the complex structure of water flow in the local scour pit around the pier, the imperfect theory of sediment transport and the random collapse of sediment in the pit, the existing coupled calculation model of water and sediment can not accurately simulate the evolution process of the local scour pit. Therefore, the changes of the flow around the piers during the local scour around the piers are studied by laboratory tests and numerical calculations. The main work is as follows: This paper introduces the events of bridge water damage caused by local scour of pier abutment at home and abroad, and discusses the importance of the variation of flow field around pier during the development of local scour to the study of local scour mechanism combined with the research status of local scour. 2) based on the principle of computational fluid dynamics, the complex three-dimensional flow field in the development of local scour of cylindrical bridge pier is numerically simulated by using RNGk- 蔚 turbulence model in Fluent and proper wall treatment. 3) the accuracy of the numerical model is verified by the circumferential velocity of the piers measured under the flat bed condition. The agreement between the two results proves the validity of the proposed method. At the same time, the complex flow around the pier under the condition of flat bed is analyzed, and the numerical simulation can well simulate the flow structure around the pier. (4) the corresponding numerical model is established based on the measured scour pit shape at different times during the scouring process of cylindrical bridge pier. The simulation results reveal the variation of flow velocity, bed shear stress, vorticity and turbulent energy with the scouring process. 5) according to the local scour test and the distribution of turbulent flow around the pier at different times, the results show that the horseshoe vortex system around the pier is the main dynamic factor that causes the local scour. In the early stage of scour, the accelerated flow at the pier side plays a leading role in the local scour of the bridge pier. With the development of scour, the effect of horseshoe vortex system on scour is increased, which is equivalent to that of the accelerating flow on the side of the pier, and the flow behind the pier is always in the wake vortex return zone. The velocity of flow is small, but its turbulence is stronger, and the sediment scouring behind the pier is mainly affected by the wake vortex and the turbulence of the flow.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：U442.3;U443.22

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