明渠弯道水流数值模拟分析

发布时间：2018-04-19 14:07

本文选题：明渠 + 弯道水流　；参考：《兰州交通大学》2015年硕士论文

【摘要】：弯道河流普遍存在于自然界中,我国的黄河自古就有九曲十八弯之称,弯道甚至可以认为是河流的基本组成单元之一,相对于顺直河道水流特性,弯道水流具有一些顺直河道水流所不具有的独特特性,如弯道水流在其弯道处水面存在明显的凹岸高凸岸低的水面横比降,从弯道横截面看,由于力矩作用存在明显的环流特性,沿弯道水流方向看,环流呈顺时针方向旋转。研究弯道水流的特性对研究泥沙输移、河道治理、岸堤防护、岸边取水口等都有极大的现实指导意义。并且随着计算机内存的不断扩大、运算速度的不断提升,借助计算机运用数值模拟方法研究弯道水流特性逐渐变得可行并趋于成熟。本文应用数值模拟方法研究了弯道水流特性的一般规律,具体内容有:(1)系统介绍国内外关于弯道水流理论知识、数值模拟的研究现状及发展趋势(2)借助ANSYS/ICEM CFD软件建立正、反相接的90°弯道物理模型并划分网格(3)借助ANSYS/FLUENT软件求解数值模型(4)从弯道水面横比降、弯道环流、纵向流速等方面对连续弯道的水流特性进行分析,并用后处理软件TECPLOT处理结果数据在对以上内容进行分析处理后,本文得出以下几点结论:(1)对于连续弯道的明渠流,水流受惯性力作用,在弯道处水面出现明显的横比降,凹岸水位恒高于凸岸水位,弯道进口处及出口处水位也受到弯道影响,水位出现波动。(2)在弯道处表流由低水位的凸岸流向高水位的凹岸,底流则正好相反,这使得凹岸泥沙输移到凸岸;两弯之间过渡段较短不足以消除前弯产生的环流时,前弯残余环流对后弯水流产生影响,在一定条件下可能形成次环流。(3)从纵向流速看,总体上沿纵向水流流速逐渐增大;在弯道进口前主流靠近凸岸,经过一段距离后,主流开始逐渐向凹岸移动,到后弯入口处主流又重新偏向凸岸,后弯出口后,经过一段距离主流回复到渠道中心处;纵向流速表层流速最大,中层流速次之,底层流速最小。(4)标准k-ε湍流模型、RNG湍流模型及RSM湍流模型计算结果表明,三种模型都能反映流动的基本趋势,但标准k-ε湍流模型对于弯道自由水面的捕捉能力差,其值较后两种湍流模型偏大,不能正确反映弯道自由水面的变化值,RNG湍流模型与RSM湍流模型结果相近,但RSM湍流模型计算时长为三者最大。
[Abstract]:Bend rivers generally exist in nature. Since ancient times, the Yellow River in China has been known as Nine Curves and Eighteen bends. The bend can even be considered as one of the basic constituent units of rivers, relative to the flow characteristics of straight river channels.The bend flow has some unique characteristics which are not found in the straight channel flow, such as the obvious concave bank high convex bank and low water surface transverse ratio drop at the bend water surface, which can be seen from the cross section of the bend.Due to the obvious circulation characteristics of torque, the circulation rotates clockwise along the bend flow direction.The study of the characteristics of bend flow is of great practical significance for the study of sediment transport, river course control, bank embankment protection and shore water intake.With the expansion of computer memory and the improvement of computing speed, it becomes more and more feasible and mature to study the flow characteristics of curved channel by means of numerical simulation method.In this paper, the general law of bend flow characteristics is studied by using numerical simulation method. The specific contents include: 1) introducing the theoretical knowledge of bend flow at home and abroad, and the present situation and development trend of numerical simulation) using ANSYS/ICEM CFD software to establish positive results.The inverse 90 掳curve physical model and grid 3) using ANSYS/FLUENT software to solve the numerical model 4) are used to analyze the flow characteristics of the continuous bend from the following aspects: the water surface transverse ratio drop, the curved circulation, the longitudinal velocity, and so on.After the analysis and processing of the above data by the post-processing software TECPLOT, this paper draws the following conclusions: 1) for the open channel flow with continuous bends, the flow is affected by inertial force, and the transverse ratio drops obviously at the water surface of the bend.The water level of the concave bank is always higher than that of the convex bank, and the water level at the entrance and outlet of the bend is also affected by the bend, and the water level fluctuates. 2) at the bend, the surface flow flows from the low water level convex bank to the high water level concave bank, and the bottom flow is just the opposite.This makes the sediment transport from the concave bank to the convex bank, and when the transition section between the two bends is short enough to eliminate the circulation produced by the forward bend, the residual circulation in the forward bend has an effect on the back bend flow, and the secondary circulation may be formed under certain conditions.On the whole, the velocity of flow along the longitudinal direction increases gradually. After a certain distance, the main stream begins to move towards the concave bank, then to the entrance of the back bend and then to the convex bank again, and after the back bend exit, the main stream begins to move towards the concave bank.After a distance from the mainstream to the center of the channel, the surface velocity of longitudinal velocity is the largest, the velocity of the middle layer is the second, and the velocity of the bottom layer is the smallest.) the standard k- 蔚 turbulence model and the RSM turbulence model are used to calculate the results.The three models can reflect the basic trend of the flow, but the standard k- 蔚 turbulence model has a poor capture ability to the free water surface of a curved channel, and its value is larger than that of the latter two turbulence models.The results of RNG turbulence model and RSM turbulence model are similar to those of RSM turbulence model, but the calculation time of RSM turbulence model is the largest.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TV133

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