【作者】 曹晓萌；

【导师】 冉启华； 顾正华；

【作者基本信息】 浙江大学 ， 水工结构工程， 2014， 博士

【摘要】 丁坝是一种常见的涉河建筑物,广泛应用于治河工程、防洪工程、航道整治工程以及河滩围垦工程中。丁坝作为人类施加于河流系统的影响,在一定程度上会对河流系统产生干扰,为了更好地发挥丁坝的各项功能,工程实际中丁坝往往以“群”的形式出现。然而,目前针对丁坝所开展的研究无论是水流特性还是冲刷机理更多地着眼于单体丁坝上下游局部河段范围内对河床或水流的局部影响,而对由一系列丁坝所组成的丁坝群对河床及水流的综合影响和累积影响涉及较少。然而,不同间距下丁坝之间的关联性不同,从而产生的累积影响不同,因此,有必要开展丁坝作用尺度划分的研究。目前,一些涉河工程(如水库、电站、堤坝、人工运河等)的累积影响研究已经开展并取得了一定的研究成果,而丁坝作为其中的一种,关于其累积影响的研究却鲜有涉及。因此,在丁坝作用尺度划分的基础上,开展不同作用尺度之下丁坝群累积效应机理的研究具有一定的学术价值,对认识和评价涉河工程群对河流健康的影响亦有重要的意义。本文首先在浙江大学建工试验大厅开展水槽试验,获得数组丁坝群流场的试验资料,随后,选取三种不同方法求解N-S方程的紊流模型和两种自由表面处理方法对丁坝群流场进行数值模拟,在综合考虑模拟精度和模拟时间的前提下,分别获得适合非淹没丁坝和淹没丁坝流场模拟的数学模型。在前人研究的基础上,采用数值水槽定性研究非淹没丁坝和淹没丁坝作用尺度的划分准则,并对每种划分准则的优缺点进行定性分析比较,以此建立丁坝群作用尺度概念体系。进一步地,对非淹没双体丁坝和淹没双体丁坝作用尺度进行定量化研究,并在此基础上探讨不同作用尺度之下非淹没丁坝群和淹没丁坝群累积效应机理。论文完成的主要工作和取得的成果如下：(1)在水槽试验获得实测数据资料的基础上,选取三种紊流模型——标准k-ε模型、雷诺应力模型(RSM)和大涡模拟(LES),并且每种紊流模型之下自由表面边界分别采用刚盖假定和VOF模型两种处理方法,将6种数学模型分别应用于非淹没丁坝群和淹没丁坝群流场模拟中,综合考虑模型计算结果与水槽试验实测数据之间的吻合程度以及模型的计算时间,得出不同研究目的之下非淹没丁坝和淹没丁坝流场数值模拟所适合的紊流模型及自由表面边界条件。(2)根据丁坝流场数值模拟模型优选的结论并结合实际计算条件,确定非淹没丁坝流场数值模拟选用标准k-ε模型和刚盖假定所组成的数学模型,淹没丁坝流场数值模拟选用标准k-ε模型和VOF模型所组成的数学模型,以此作为工具,对不同间距之下非淹没双体丁坝和淹没双体丁坝的流场进行比较分析,提出三种非淹没丁坝群作用尺度划分准则——基于大尺度涡不相重叠、基于双丁坝断面流速分布相似和基于下游丁坝断面流速分布恢复,通过对三种划分准则的定性分析比较,分别得出三种划分准则的优缺点及适用范围；同时,提出一种淹没丁坝群作用尺度划分准则——基于下游丁坝断面流速分布恢复,通过定性分析,得出该划分准则的优缺点及适用范围。(3)通过量纲分析分别获得非淹没双体丁坝和淹没双体丁坝间距阈值的影响因素,并据此拟定数值试验工况；采用数值模拟的手段分别开展非淹没双体丁坝和淹没双体丁坝作用尺度量化研究,得出三种非淹没丁坝划分准则之下丁坝间距阈值的经验公式,定量比较三个公式的计算结果发现,基于大尺度涡不相重叠划分准则的计算结果偏小,后两者计算结果相当,机理分析表明,后两者本质相同但适用范围差异较大,前者是非淹没丁坝作用尺度判断的必要非充分条件；同时,获得淹没双体丁坝划分准则之下间距阈值的经验公式,并进一步对非淹没双体丁坝和淹没双体丁坝间距阈值进行横向定量比较。(4)最后,以非淹没双体丁坝三个间距阈值经验公式为基础,分别对三种作用尺度之下非淹没丁坝群水流结构、水流时均流速以及紊流强度等要素的累积效应机理进行探讨,通过对比分析发现,不同作用尺度之下非淹没丁坝群水流要素的累积效应有所不同,随着相邻丁坝间距增大作用尺度增大,累积影响最先消失的是水流结构,其次是水流时均流速,最后是紊流强度；以淹没双体丁坝间距阈值经验公式为基础,分别对两种作用尺度之下淹没丁坝群水面高度、水流时均流速以及紊流强度等要素的累积效应机理进行探讨,研究发现随着丁坝个数的累加,淹没丁坝群水面高度和水流时均流速的累积变化规律相反并且累积影响同时消失,而紊流强度仍然是其中最难恢复的水流要素。更多还原

【Abstract】 Spur dike is one of the common river engineerings, which is widely used in river training projects, flood control projects, channel improvement projects and floodplain reclamation projects. As a human impact imposed on river system, spur dike would interfere river system to a certain extent. In order to better play the various functions of spur dike, spur dike often appears in the form of "group" in engineering practice. However, the current researches on spur dike, including flow characteristics or local scour mechanism, are more concentrated in partial impacts of single spur dike on the flow or riverbed and confined in the range of local reaches to the upstream or downstream spur dike. It is less involved in the combined effects and cumulative effects of spur dike group composed by a series of spur dikes on the flow or riverbed. In addition, the correlation between spur dikes is different under different dike spacing, so the corresponding cumulative effects are different. Consequently, it is necessary to carry out the research of impact scale of spur dikes. Currently, the cumulative effect studies of some river engineerings, such as reservoirs, hydropower stations, dams, artificial channels, etc., have been carried out and achieved some research achievements. However, as one of them, cumulative effect researches of spur dike are rarely involved. Therefore, based on the classification of impact scale of spur dikes, to carry out the research of cumulative effect mechanism of spur dike group with different impact scales has some academic value and important significance for understanding and evaluating the impact of river engineering on river system health.Firstly, flume experiments were conducted in Jiangong Testing Hall of Zhejiang University to obtain observed data of flow field of spur dike group. And then, three turbulence models based on different solutions of N-S equations and two kinds of treatment methods of free surface were selected to simulate the spur dike flow field. Under the comprehensive consideration of simulation accuracy and computation time, the suitable mathematical models of non-submerged and submerged spur dikes were obtained. On the basis of previous studies, numerical simulation was used to study on the classification criteria of impact scale of non-submerged and submerged spur dikes, and the advantages and disadvantages of each classification criterion were analysed and compared, meanwhile, the concept system of impact scale of spur dike group was built. Furthermore, the impact scale of non-submerged and submerged spur dikes was researched quantitatively and the cumulative effect mechanism of non-submerged and submerged spur dikes under different impact scales were carried out further. The major work and conclusions of the thesis are as follows:(1) Based on the observed data from flume experiments, three turbulence models--standard k-ε model, Reynolds stress model (RSM) and large eddy simulation (LES)-were selected, and the free surface boundary respectively employed two methods--rigid-lid assumption and VOF method (volume of fluid) in each model. The six kinds of mathematical models were applied to the simulation of flow field of non-submerged and submerged spur dike. Considering the consistent degree between computed results and observed data as well as the model computation time, the appropriate turbulence model and free surface boundary for the simulation of flow field of non-submerged and submerged spur dike were obtained under different research purposes.(2) According to the conclusions of appropriate mathematical models of non-submerged and submerged spur dikes and the actual computation condition, mathematical model contained in standard k-ε model and rigid-lid assumption was utilized to simulate the flow field of non-submerged spur dike, and mathematical model combined by standard k-ε model and VOF model was used to simulate the flow field of submerged spur dike. Based on above mathematical models, the flow fields of non-submerged and submerged spur dikes with different spacing were simulated and analyzed. Three classification criteria of impact scale of non-submerged double spur dikes were proposed, which respectively based on non-overlapping of large-scale vortex, similarity of sectional velocity of double spur dikes and velocity recovery of downstream dike, and their advantages, disadvantages and application scopes were analyzed qualitatively. Meanwhile, a classification criterion of impact scale of submerged double spur dikes based on velocity recovery of downstream dike was proposed, and its advantages, disadvantages and application scopes were gotten by qualitative analysis.(3) The influence factors of spacing threshold of double non-submerged and submerged spur dikes were obtained by dimensional analysis and the corresponding simulation conditions were drawn up respectively. The quantitative research of impact scale of double non-submerged and submerged spur dikes were carried out by means of numerical simulation. Three empirical formulas of spacing threshold of double non-submerged spur dikes under three classification criteria were obtained. The comparion of calculation results from three formulas showed that the results based on non-overlapping of large-scale vortex were smallest, while the results from the other two were with little difference. Mechanism analysis showed that the latter two had the same essence but different applied scope, and the former criterion was the necessary but not sufficient condition for the judgment of impact scale of non-submerged spur dikes. Likewise, the empirical formula of spacing threshold of double submerged spur dikes under the classification criterion was obtained. And the quantitative comparison of spacing thresholds between non-submerged and submerged spur dikes was carried out further.(4) Finally, based on the three empirical formulas of spacing threshold of double non-submerged spur dikes, the cumulative effect mechanism of flow structure, velocity and turbulence intensity of non-submerged spur dike group under three kinds of impact scales were explored respectively. Comparison study showed that the cumulative effects of each flow component of non-submerged spur dike group were different under different impact scales. With the increase of spacing between adjacent dikes, the cumulative effects of flow structure were the first to disappear, followed by flow velocity and turbulence intensity. Similarly, based on the empirical formula of spacing threshold of double submerged spur dikes, the cumulative variation of water level, flow velocity and turbulence intensity of submerged spur dike group under different impact scales were discussed respectively. It was found that with the accumulation of the number of spur dike, the cumulative variation of water level and flow velocity were inverse and the cumulative effects almost disappeared simultaneously, while turbulence intensity was still the most difficult to recover among the flow factors.更多还原