兰州大学机构库 >土木工程与力学学院
风沙跃移运动的数值模拟
Alternative TitleNumerical Simulation of Wind-Blown Sand Saltation
樊莉
Thesis Advisor武生智
2011-05-31
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword跃移 输沙量 风速廓线 阻力系数 非均匀沙 粒径分布
Abstract风沙跃移运动的数值模拟 中文摘要 风沙跃移是风沙流中沙粒的主要输移方式,在跃移层内沙粒大量聚集,颗粒间的相互作用及其复杂,目前还不能从微观的角度得到精准的颗粒间作用力、动量及能量交换情况。当前大多数对跃移颗粒的研究,采用单个圆球颗粒的阻力系数公式,没有考虑到当越来越多颗粒聚集起来时对阻力系数公式的影响。在荒漠里的天然沙中,沙粒形状复杂多样,粒径大小也各不相同,当粒径分布不同时,跃移运动也会不同。然而,目前大多数对风沙跃移的数值计算和实验研究致力于均匀沙的跃移。因此,准确刻画颗粒群体行为和对非均匀沙的跃移研究显得非常必要。为研究更加接近实际情况的跃移运动,并为实验研究提供一些理论分析和数值资料,本学位论文研究了颗粒群阻力效应和几种粒径分布对跃移运动的影响。研究内容包括: 1.采用修正后的单球模型阻力系数公式改进了已有的风沙耦合模型,计算了跃移运动达到稳定状态时的风速廓线、输沙量及沙粒相体积分数。计算结果表明,考虑颗粒群阻力效应对风沙跃移的影响是必要的,用修正后的阻力系数公式计算所得的输沙量及沙粒相体积分数均大于相同高度处、不修正的相应值。另外,修正之后输沙量、沙粒相体积分数随摩阻风速增大而增大的定性关系并未改变,同时,随着摩阻风速的增大以相同速度起跳的颗粒跃移长度随之增大,其跃移高度有所降低。 2.用数值计算的方法模拟了几种不同粒径分布方式相应的风沙跃移运动。分别计算了沙粒为单一粒径以及粒径数学期望为该值时的随机分布和均匀分布,共七种情况下的风沙跃移运动。计算结果表明,对于相同风速,气流对单一粒径组成的均匀沙的携带能力较弱,而对由多粒径组成的非均匀沙的携带能力较强。同时,沙粒粒径分布的不同导致当跃移运动达到稳定时,风沙流饱和层的高度和沙粒的跃移长度、高度均有所变化。 关键词:跃移,输沙量,风速廓线,阻力系数,非均匀沙,粒径分布
Other AbstractNumerical Simulation of Wind-Blown Sand Saltation Abstract Saltation is the most important transfer and shift way of wind-blown sand. A great number of sand grains gather in the saltation layer, where the interaction between the grains is very complicated. So far we cannot figure out the accurate status of interaction forces, momentum and the energy exchange at the micro level. Most works on wind-blown sand flow use standard drag coefficient formula for single sphere particle to study sand movement in saltation,but failing to concern about the particle swarm effect when more and more grains move together. The natural sand grains from desert have various forms and different diameter sizes. When diameter size distribution changes, corresponding saltation changes too. Yet, most of aeolian physics research in literature focuses on field observation of wind blown sand and numerical simulation for saltation of sand grains with the uniform diameters. Therefore, the numerical study for nonuniform sand grains is very necessary. In order to study the compicated sand saltation in the real world and to provide some reference for further theoretical analysis and numerical research, this paper discusses the influence of grains swarm and several diameter size distributions to sand saltation. The main content includes: 1. A modification of drag coefficient by grains’ volume density is introduced to the original windblown sand model. Using the modified model, we calculate the mass flux,wind speed profile as well as grains’ volume density in steady state of wind-blown sand movements.The numerical results display that both mass flux and grains’ volume density calculated with modified model are larger than those calculated by standard model, but the wind speed is insensitive to this kind of modification.In addition, it turns out that when the friction velocity increases,mass flux and grains’ volume density increases as well. This means that the effect of particle swarm on saltation is of importance and should be considered in further study. 2. A computational method is employed to simulate saltation movements of sand grains with various diameter size distributions. In this paper, we analyzed seven kinds of saltation movements respectively, in case of particles with different particle size distributions. The results show that the air flow has more powerful transporting ability for nonuniform particles than that for uniform particles under the same wind conditions....
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Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226509
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
樊莉. 风沙跃移运动的数值模拟[D]. 兰州. 兰州大学,2011.
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