沙尘输运对脉动风响应的数值模拟研究 Alternative Title Numerical simulation of the response of dust and sand transport to fluctuating wind 彭晓庆 Thesis Advisor 谢莉 2013-05-25 Degree Grantor 兰州大学 Place of Conferral 兰州 Degree Name 硕士 Keyword 定常和非定常来流 输沙率 响应时间 阵风 Abstract 沙尘在实际脉动或阵风风场中的输运规律不同于定常来流风场下的输运规律。输沙对不同脉动参数的风场具有不同程度的响应，因而导致了输沙率、输沙结构等物理量的差别，故对该响应规律的准确认识对理解实际沙尘的输运规律和输运性质进而准确预测沙尘暴具有重要意义。本学位论文针对跃移风沙流输沙率对变化风场的响应时间以及沙尘在阵风作用下向高空的输运规律展开数值模拟研究。主要工作如下： 1、针对击溅函数的选择对风沙流数值模拟结果的影响展开研究。分析四种典型击溅函数在不同的来流风场下的溅起沙粒数、风沙流结构(输沙率沿高度的分布)以及输沙率的差别。结果表明，利用Kok & Renno的击溅函数模拟的输沙率可以获得与现有的风洞实验一致的结果，同时也描述了输沙量沿高度出现分层点的变化规律。 2、基于定常与非定常来流下的风沙流模型，开展了输沙率对风场响应时间的数值模拟研究。结果表明：定常来流下，当风场突然加速时，响应时间随初始来流平均风速增大而减小，随粒径增大而增加；当风场突然减速时，则表现出相反的规律。正弦风场来流下，输沙率对风场响应时间均随平均风速及振幅增大而减小，随周期增大而增大，并在周期为20s左右时趋于常值；且波峰的加速响应时间要小于波谷的减速响应时间。 3、开展了沙尘在阵风作用下输运规律的数值模拟研究。结果表明：沙尘的垂向输运高度和水平输运距离随粒径增大而减小，且小粒径对风的跟随性比大粒径要好；混合粒径情况下，空中的粒径分布和床面的初始粒径分布规律一致，空中平均粒径与距离地面高度相关，当高度在10m-20m之间时，平均粒径开始减小。 Other Abstract Dust and sand transport law shows differences between the actual fluctuating or gust wind field and steady wind flow. The response time of sand transport rate to varies with fluctuating parameters of wind field, which leads to the differences of the sand transport rate, sand structure and other physical quantities. And the response degree is of great significance for understanding the actual dust transport law, transport properties, which is benefit of accurately predicting of dust storms. The thesis focus on the response time of sand transport rate to wind speed fluctuations of near-surface saltation sand flow and the dust transport law of high-altitude in the role of the gust. The main works are concluded as following, 1. We simulate splashing sand number, sand flow structure (sediment transport rate along the height distribution) and sand transport rate wind-sand flux by using flow typical splash functions. By comparison of results, it can be found that the sand transport rate simulated by the splash function reported by Kok & Renno can be consistent with results measured in wind tunnel, and simulated results can also describe the law of the stratified point along height for sand transport rate. 2. Based on the steady-state and unsteady wind-blown sand model, we simulate the response time of sand transport rate to wind speed. It is found that the response time decreases with the increase of flow average wind speed, and increases as the particle size increases in the steady stream; nevertheless, the response time of sudden deceleration of the flow displays instead of the law. The response time in the sinusoidal wind stream decreases with increasing the average wind speed and amplitude, and increases with increasing of the cycle; and the time tends to a constant value at about 20s as the cycle increases. In addition, the peak acceleration response time is less than the valley deceleration response time. 3. The study of dust and sand transport in gusts wind is carried out through numerical simulation. It is found that the transport height and horizontal distance decreases with the increase of the grain size, and the smaller particles can follow the wind more easily for the dust and sand transport. In case of a mixed particle diameter, the particle size distribution in the air depends on the particle size distribution of initial bed. The average particle diameter is related to the height from the ground. When the height is between 10m and 20m, mean par... URL 查看原文 Language 中文 Document Type 学位论文 Identifier https://ir.lzu.edu.cn/handle/262010/226004 Collection 土木工程与力学学院 Recommended CitationGB/T 7714 彭晓庆. 沙尘输运对脉动风响应的数值模拟研究[D]. 兰州. 兰州大学,2013.
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