新月形沙丘风场的数值模拟 Alternative Title Simulation of flow over an isolated barchan dune 江丽娟 Thesis Advisor 郑晓静 2009-05-31 Degree Grantor 兰州大学 Place of Conferral 兰州 Degree Name 硕士 Keyword 数值模拟 新月形沙丘 气流加速 剪应力分布 回流区长度 保护区长度 侧坡风速 绕流加速 Abstract 沙粒运动，气流和地表形态三者是相互耦合的关系，特别是对沙丘附近流场的研究有利于认识沙粒的侵蚀和沉积，进而探明沙丘形成和移动机制。而目前对新月形沙丘流场的详细分析较少，如迎风坡气流加速过程和影响回流区长度的因素，以及沙丘背风坡的保护区长度等。本文利用通用CFD软件FLUENT数值模拟了二维和三维孤立新月形沙丘附近的流场。 第二章侧重于前坡气流加速特征的讨论，如沙丘高度、沙丘迎风坡坡度以及坡前来流风速对摩阻加速因子的影响，并由摩阻加速因子与上述因素的相关性拟合出了摩阻加速因子的公式；第三章分析了背风坡回流区长度和保护区长度与沙丘高度、来流风速之间的关系等；第四章则初步探讨了三维新月形沙丘表面流场结构，主要分析了侧坡风速沿着沙丘高度加速情况，同时也比较了同一高度处侧坡风速与迎风坡风速之间的关系；对沙丘表面的剪应力分布也进行了初步分析讨论。 结果表明：对于二维的数值模拟，沙丘高度是影响迎风坡气流加速的主要因素，沙丘高度越高，迎风坡气流加速越大，而来流风速对迎风坡气流加速的影响与沙丘高度比较，是小量可以忽略；回流区长度和保护区与沙丘高度的比值随着高度的增加而增加。对于三维的数值模拟，气流绕沙丘有着明显的加速现象，并且沿着沙丘高度，加速程度呈现大-小-大的变化趋势。剪应力分布相对于二维来说，沿着y方向有着明显不同的分布。在沙丘中下部，侧坡剪应力比同一高度处的迎风坡和边缘线处的剪应力都要大；沿着高度的增加，三处的剪应力值有逐渐相等的趋势；两个丘臂尾部气流存在被加速的现象等。 Other Abstract The relationships among sand flux, wind flow and topography are complex and coupled. Studying flow field near the dunes is useful to understand the process and mechanics of dunes formation. And there are only countable papers including detailed analysis about flow over an barchan dune, such as flow acceleration up the stoss slope and what influences separation length in the lee side. This paper simulated flow over an isolated barchan dune with different aspect rations by computational fluid dynamics (CFD) software. In chapter 2, we focus on flow acceleration up with the stoss slope. For example, we analyze the relationships between speed-up factor and dune height, the angle of the stoss slope, wind-speed. And according to these relationships, we derived a formula of the speed-up factor. In chapter 3, we simulate flow over an isolated barchan dune employing commercial software CFD from FLUENT Inc., and discusse how the dune height and upwind speed to influence the separation length, protection length. After we analyzed reverse flow in the lee-side, we proposed that dune height plays a important role in leading to the more extent of the flow acceleration. The increment of wind-speed at the dune crest increases with higher dune. And upwind speed also can influence the increment of the wind-speed up the stoss slope, but comparing with the role of the dune height, this increment is small. Separation length in the lee-side also increases with dune height. In chapter 4, we simulate flow field around a 3D barchan dune, and analyze the relationship between the air flow and sand ripple on the dune surface, and preliminarily discuss the distribution of the shear stress on the dune surface. The results show that there exists apparent acceleration up the side slope, and around the dune. And the shear stress distribution is also very different from the 2D simulation, especially at the horn toe, flow was accelerated apparently. URL 查看原文 Language 中文 Document Type 学位论文 Identifier https://ir.lzu.edu.cn/handle/262010/225840 Collection 土木工程与力学学院 Recommended CitationGB/T 7714 江丽娟. 新月形沙丘风场的数值模拟[D]. 兰州. 兰州大学,2009.
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