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1.
通过砾质戈壁风沙流野外实测数据的分析以及风洞模拟实验研究发现：戈壁风沙流结构具有与沙漠风沙流完全不同的风沙流特征,戈壁风沙地表的粗糙度随风速的增大而增加,其表面风沙流输沙量高度分布表现出独特的"象鼻"效应,在一定高度处呈现最大值,并随风速的增加而增高。该"象鼻"效应导致戈壁风沙流结构特征值λ远大于 1,不论风速多大,风沙流都处于未饱和状态的非堆积搬运状态。这种特殊性质比较清楚地解释了敦煌莫高窟千年来不被沙山埋没的谜底。并且在风沙防治工程实践中,采用砾石压沙措施,构造类似与砾质戈壁的下垫面,人工促使风沙流结构呈现"象鼻"形状,可使防沙工程达到理想的输导作用。 相似文献
2.
戈壁风沙流结构特性及其意义 总被引：31，自引：2，他引：29
通过砾质戈壁风沙流野外实测数据的分析以及风洞模拟实验研究发现：戈壁风沙流结构具有与沙漠风沙流完全不同的风沙流特征,戈壁风沙地表的粗糙度随风速的增大而增加,其表面风沙流输沙量高度分布表现出独特的“象鼻”效应,在一定高度处呈现最大值,并随风速的增加而增高。该“象鼻”效应导致戈壁风沙流结构特征值A远大于1,不论风速多大,风沙流都处于未饱和状态的非堆积搬运状态。这种特殊性质比较清楚地解释了敦煌莫高窟千年来不被沙山埋没的谜底。并且在风沙防治工程实践中,采用砾石压沙措施,构造类似与砾质戈壁的下垫面,人工促使风沙流结构呈现“象鼻”形状,可使防沙工程达到理想的输导作用。 相似文献
3.
突水溃沙是西部矿井地质灾害的主要类型之一,为研究突水溃沙灾害的临界判据与水沙运移特征,以榆横矿区含水层风积沙为例,采用自主研发的水沙两相高速渗流试验设备,对4种不同粒径范围的风积沙进行了沙粒起动试验和溃沙试验,对混合风积沙进行了水沙两相高速渗流试验。得到了影响突水溃沙的2个临界速度条件：第一临界速度即沙粒起动速度,为0.38～1.26 mm/s;第二临界速度即溃沙临界速度,为2.48～3.54 mm/s。试验结果表明：体积膨胀是沙粒群起动的必要条件,突水溃沙灾害是起动的风积沙由量变逐步积累到质变的物理过程,分为3个阶段：（1）水携沙流动,（2）水沙混合流动,（3）沙携水流动。沙粒起动是水动能转变为沙动能的过程,溃沙时水沙混合流体运动表现为颗粒群浓度波传播的特征,沙粒间通过碰撞的形式传递能量。溃沙速率随初始水力梯度的增大呈指数增长,单位时间内溃沙量随水力梯度的增大而呈线性增加。 相似文献
4.
非平稳风沙运动研究进展 总被引：1，自引：1，他引：0
风蚀输沙起动条件与输沙率预测是风蚀预报、沙尘数值预报与风沙地貌演化以及防沙治沙工程研究所需的关键参数,因而一直是风沙物理学研究的重点课题。早期的研究主要关注稳态输沙过程,对野外实际输沙过程的预测存在相当大的误差。近年高频的实时同步输沙、风速测量显示:大气边界层近地表风速脉动强烈,因而导致野外实际输沙具有高度的时空变化。研究发现:风沙输运的非平稳特性与边界层湍流结构密切相关,因而会对沙粒起动条件判断、输沙率预测等产生影响。回顾了近20年中非平稳输沙研究在实验、理论以及数值模拟方面的进展,并提出了目前存在的问题和今后发展的趋势。 相似文献
5.
基于Fluent气固两相流,运用 湍流模型,对风沙环境下沙漠路基的风蚀破坏规律进行数值模拟研究。分析路基不同横断面下风沙流扰动、增速、减速、恢复的过程,以及路基障碍物的存在对风沙流扰动后造成的风速减弱区和恢复区,总结路基坡面特征点的风速变化规律,与现场实测结果作比较,二者具有很好的一致性。研究结果表明,不同路基横断面下风速减弱区和恢复区的分布对路基高度变化敏感,受边坡坡率的影响较小,不同路基高度、不同边坡坡率下路基沿程风速变化明显不同。边坡坡率一定,随路基高度的增加,路基周围流场扰动被增强,迎风坡坡顶风速增大显著,背风坡坡底风速下降愈明显;路基高度一定时,边坡坡率越小,路基沿程风速变化越平缓。当边坡坡率为1:3时,路基模型高度由1m增加到3 m时,迎风坡坡顶风速增加12%,背风坡坡底风速降低约80%。建议为避免沙漠路基的风蚀破坏,路基高度不宜太大,边坡坡率较小为宜。 相似文献
6.
沙漠公路风蚀破坏规律的数值模拟研究 总被引：1，自引：0，他引：1
通过Fluent软件对沙漠公路的风蚀破坏规律进行数值模拟研究。分析公路不同横断面时风沙流扰动、增速、减速、恢复的过程,确定路基(堑)高度、边坡坡率和路面宽度等公路断面设计参数对风沙流扰动的影响,提出沙漠公路路基(堑)风蚀破坏规律。结果表明：路面宽度的改变对路基沿程风速变化影响较小,各特征点处风速变化小于5%。路基(堑)高度和边坡坡率对风沙流扰动的影响较大。随路基(堑)高度增加,风沙流流场的扰动被增强,路基(堑)风蚀破坏越显著,当边坡坡率为1:1时,路基模型高度250 mm时的迎风路肩风速为模型高度60 mm时的 1.15倍,其背风坡脚风速降低45%;路堑模型高度250 mm时的背风堑顶风速为模型高度60 mm时的1.05倍,迎风堑脚处风速降低高达80%。建议沙漠公路宜采用中低路基(堑),不宜高填深挖。当路基(堑)高度一定,边坡坡率为1:1.75或1:2时,路基(堑)沿程风速变化平缓,沙漠路肩不易被吹蚀破坏;路堑中堑脚位置处不易出现堆积。其结论与室内风蚀风洞试验结果有很好的一致性 相似文献
7.
沙漠公路风沙土路基风蚀破坏试验研究 总被引：2，自引：0，他引：2
以沙漠公路风沙土路基为研究对象,通过室内风蚀风洞试验研究路基的风蚀破坏规律,以及路基不同断面对风沙流运动的影响。以路基高度、路基边坡坡率和路基宽度作为路基断面主要设计参数,研究不同路基断面下风沙流扰动、增速、减速、恢复的过程,以及路基周围风速流场的变化特征,分析路基病害较未病害时路基周围流场的变化。试验结果表明：路基高度和边坡坡率对风沙流运动的影响较大。随路基高度增加,路基对风沙流流场扰动增强,迎风坡坡顶处吹蚀破坏和背风坡坡底处堆蚀破坏越显著,在确定的路基边坡坡率下,路基模型高度为250 mm较模型高度为60 mm时,迎风坡坡顶风速增加1.13倍,背风坡坡底风速减小2.53倍,建议沙漠公路路基高度宜小于2.5 m。进一步,在确定的路基高度下,比较不同的边坡坡率对路基沿程风速的影响,发现当路基边坡坡率为1:1.75时,路基沿程风速变化不明显,沙漠公路风沙土路基不宜被风蚀破坏。 相似文献
8.
风蚀坑是沙质草原沙漠化的主要地貌响应和驱动,但目前我们对其形成演化的动力机制知之甚少。利用二维超声风速仪和积沙仪观测了共和盆地不同发育阶段风蚀坑表面气流和风沙流特征,研究其形态—动力反馈过程。结果表明:(1)风蚀斑与碗状坑内气流沿主风向先减速后加速,槽形坑内气流则先辐散减速—中部气流加速—积沙体迎风坡风速降低—背风坡风速有所恢复;且发育初期风蚀坑内风速与风速变异系数和风向稳定系数均呈负相关,而发育中期坑内风速与前者呈正相关,与后者呈负相关。(2)受坑体内的涡流影响,槽形坑内风速廓线不符合对数分布规律。(3)槽形坑内不同部位的输沙率随高度均呈指数式递减,但受气流—形态间的反馈作用,各部位输沙通量差异明显,坑底最低、积沙体迎风坡前端最大。风蚀坑内气流场与形态间存在反馈关系,坑体越大反馈效果越明显。 相似文献
9.
风沙物理学的发展与展望 总被引：9，自引：0，他引：9
介绍了风沙物理学研究在土壤风蚀、沙粒跃移和风沙流结构等方面取得的一些进展。展望了风沙物理学在地表风蚀、沙物质的风力搬运和沉积、风成地貌理论和相似理论、风沙工程理论与应用等研究领域的发展前景。针对我国的实际情况,提出了加强风沙物理学研究的建议。 相似文献
10.
干旱区防沙林带风沙沉积粒径变化及其动力学意义 总被引：1，自引：0，他引：1
通过野外地表沉积采样、植被调查和风速观测,本文对塔克拉玛干沙漠防护林带内地表风沙沉积粒径变化进行了研究.主要结论如下:1)防沙林带内沉积具有沙丘沙单峰分布的特征,在沙垄不同地貌部位,单峰对应的粒径区间存在粗细差异,与大地形的侵蚀堆积分布有关;2)EOF(经验正交函数)分解的第二特征向量与植株中上层高度的风速具有较好的相关性,反映了防护林带内外沉积动力的变化;3)由第二特征向量确定了粗、细敏感粒级的粒径分界范围为109.4～ 125.6μm,敏感粒级组分的百分含量与风速存在线形关系;4)使用敏感粒级组分的百分含量可评价沙垄各断面林带防护效益,林带内外粗、细敏感粒级组分的含量差异多在10％以上.研究结果反映了极端干旱环境下,风力变化对地表沉积粒径变化的影响,可以为工程防沙效益评价以及风沙沉积研究提供参考. 相似文献
11.
YanYan Yang LianYou Liu XiaoYan Li PeiJun Shi GuoMing Zhang YiYing Xiong YanLi Lyu LanLan Guo Bo Liang MengDi Zhao JiaDong Dai XiYang Zuo XuJiao Han 《Sedimentology》2019,66(2):590-603
Aeolian sand entrainment, saltation and deposition are important and closely related near surface processes. Determining how grains are sorted by wind requires a detailed understanding of how aerodynamic sand transport processes vary within the saltating layer with height above the bed. Grain‐size distribution of sand throughout the saltation layer and, in particular, how the associated flux of different grain size changes with variation in wind velocity, remain unclear. In the present study, a blowdown wind tunnel with a 50 cm thick boundary layer was used to investigate saltating sand grains by analyzing the weight percentage and transport flux of different grain‐size fractions and the mean grain size at different wind velocities. It was found that mean grain size decreases with height above the sand bed before undergoing a reversal. The height of the reversal point ranges from 4 to 40 cm, and increases with wind velocity following a non‐linear relationship. The content of the finer fractions (very fine and fine sand) initially increases above the sand bed and then decreases slightly with height, whereas that of the coarser fractions (medium and coarse sand) exhibits the opposite trend. The content of coarser grains and the mean grain size of sand in the saltation layer increase with wind velocity, indicating erosional selectivity with respect to grains in multi‐sized sand beds; but this size selectivity decreases with increasing wind velocity. The vertical mass flux structure of fine sand and very fine sand does not obey a general exponential decay pattern under strong wind conditions; and the coarser the sand grain, the greater the decrease rate of their transport mass with height. The results of these experiments suggest that the grain‐size distribution of a saltating sand cloud is governed by both wind velocity and height within the near‐surface boundary layer. 相似文献
12.
An experimental study was undertaken in a large-scale wind tunnel to investigate sand particle dislodgement by wind over time in the absence of grain-bed collisions. Aerodynamic dislodgement was measured for six groups of sand particles under two known wind velocity profiles. The results show that the dislodgement rate for both fine and coarse particles decreases rapidly during the transition of the particle surface from a non-wind-worked condition to a wind-worked condition, and that the dislodgement rate continues to decay under a wind-worked condition even though the mean grain size of surface particles remains nearly the same. A previously developed theoretical method for calculating the number of particles left on the bed by wind was developed further. The derived method was used to calculate the time-decay of the dislodgement rate and the length of time required for the dislodgement rate to reach an equilibrium. The length of time for dislodgement rate to reach an equilibrium in this study is of the order of 10–15 min. This not only provides further observation of the second, long stage of aeolian sediment transport system development reported previously but also indicates a potentially large variation in the time-decay of transport rate under different conditions. The results indicate that the time-decay of the particle dislodgement rate is related to sorting processes. Because of the artificial method of preparation of the grain surface and the wind velocity profiles, the results of this study should be applied with caution to natural conditions. 相似文献
13.
《Sedimentology》2018,65(6):1859-1874
Ripples are prevalent in aeolian landscapes. Many researchers have focused on the shape and formation of sand ripples, but few have studied the differences in the particle size of sand on crests and in troughs along bed, especially the variations caused by changes in friction velocity and the wind‐blowing duration. A particle size of 158 μm (d ) was used to create aeolian ripples in a wind tunnel under four friction velocities (u *) with different wind duration times (t ). Samples were collected from the surfaces of ripple crests and troughs, respectively, at seven sites, and particle sizes were measured using a Malvern Mastersizer 2000. The main results were: (i) The particle size distributions of sand in troughs are unimodal with slight variations of particle size parameters, including mean particle size, standard deviation, skewness and kurtosis, etc., under different conditions, while these particle size parameters of sand on crests change with friction velocity and deflation time. Moreover, some of the particle distribution curves for the sand on crests do not follow typical unimodal curves. (ii) With increasing friction velocity or deflation duration, the sand on the crests shows a coarsening process relative to those on the bed surface. The particle size of sand on crests at a 1 m bed increases linearly with friction velocity (d = 344·27 + 34·54 u *) at a given wind‐blowing duration. The particle sizes of sand on crests at 1 m, 2 m and 4 m beds increase with a power‐law relationship (d = a + t b, where a and b are fitting parameters) with deflation time at a given friction velocity. (iii) The probability cumulative curves of sand showed a three‐section pattern in troughs and on most of the crests but a four‐section pattern at crest locations due to increased influence by friction velocity and deflation time. The proportions of the sediment moved by suspension, saltation and creep in the three‐section pattern were within the ranges of 0·2% to 2·0%, 97·0% to 98·9%, and 0·8% to 3·0%, respectively. For the four‐section pattern, suspension accounted for 0·3% and 3·0%, and the proportion of creep increased with friction velocity and deflation time, while saltation decreased accordingly. Although these results require additional validation, they help to advance current understanding of the grain‐size characteristics of aeolian ripples. 相似文献
14.
Qingjie Han Jianjun Qu Kongtai Liao Kecun Zhang Ruiping Zu Qinghe Niu 《Environmental Earth Sciences》2012,67(1):243-250
In this study, wind tunnel tests were performed to determine the relationships between sediment transport, the surface moisture content, and wind velocity using beach sands from a tropical humid coastal area of China. The variation in the properties of the creep proportion, relative decay rate as a function of height, and average saltation height in the flux profile were determined. Sand transport was measured using a standard vertical sand trap. The creep proportion (i.e., the proportion of the particles that move along the surface rather than undergoing saltation) and relative decay rate decreased and more particles were ejected to higher positions as moisture content and wind velocity increased. The creep proportion ranged between 0.12 and 0.33, and averaged 0.22. The creep proportion and relative decay rate decreased abruptly at moisture contents between 0.587 and 1.448%; the latter value was close to 1.591%, the moisture content at a matric potential of ?1.5 MPa. This moisture content limit may indicate a change in the form of soil water from adsorbed films on particle surfaces to capillary forces created by inter-particle water bridges. The surface moisture content therefore appears to decisively determine the degree of the restraint on particle entrainment by the wind. The average heights, below which 25, 50, 75, and 90% of sand transport occurred, increased with increasing moisture content (except at 0.231% moisture content) and wind velocity. The mean saltation height at various wind velocities increased linearly with increasing moisture content. 相似文献
15.
风沙流对植物生长影响的研究 总被引：19，自引：1，他引：19
在中国乃至全球，风沙活动都十分频繁，它直接影响着风沙地区植物资源的可持续利用与发展，因此，研究风沙流对植物生长的影响十分必要。以往，相关的研究主要是围绕沙漠逆境的综合条件（如降水、温度、湿度、土壤水分、养分等综合因子）进行的，研究内容涉及植物的生理、生化、物质代谢以及生态适应性等。但国内外就风沙流单因子对植物生理生化影响的研究还没有深入展开，为此，作者利用野外风洞条件，就不同风况下的风沙胁迫对某些植物生长特征的影响进行了实验研究；结果表明：风沙流胁迫可使植物的净光合速率（Pn）、气孔导度（Cs）、叶温（Tl）、叶片水势（Wp）降低，使蒸腾速率（Tr）升高；且风速越大，吹风间隔越短，这些参数变幅越大；风沙流比净风的影响更大。风沙流能降低试验植物的水分利用率，进而增加植物的干燥作用；同时可使脯氨酸含量增加。由于风沙流运动和植物的复杂多样性，因此这个研究领域还有许多问题需要探索。 相似文献
16.
Blown sand has caused considerable damage to the Dunhuang Mogao Grottoes of China. Controlling the blown sand requires a clear understanding of the processes that govern its production and movement. Experiments were conducted in a wind tunnel and in the field to define the relationships between sand production and gravel coverage in the gobi above the Mogao Grottoes. The gravel that covers the gobi’s surface controls wind erosion, irrespective of its shape and size. The equilibrium coverage by gravel over which no further sand is emitted due to wind erosion increases and the equilibration time that is taken to form the equilibrium gravel coverage decreases with increasing wind velocity. Gravel coverage has reached an equilibrium state in the portion of the gobi directly above the grottoes, but decreases towards the Mingsha Mountains. Drifting sand from these mountains is the main source of sand damage at the Mogao Grottoes. If no additional sand from the mountains were supplied to the gobi, gravel pavements would reach an equilibrium level of coverage and prevent further production of blowing sand. Sand blown from the gobi represents secondary reactivation of sediments originally produced in the Mingsha Mountains. Therefore, to control the blowing sand above the Mogao Grottoes, emphasis should be placed on controlling erosion from the Mingsha Mountains rather than local erosion of sand in the gobi. 相似文献
17.
Air density effects on aeolian sand movement: Implications for sediment transport and sand control in regions with extreme altitudes or temperatures 总被引：3，自引：0，他引：3 
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下载免费PDF全文 Aeolian sand transport results from interactions between the ground surface and airflow. Previous research has focused on the effects on sand entrainment and mass transport of surface features and wind velocity, but the influence of air density, which strongly constrains airflow characteristics and the resulting sand flow, has not been widely considered. In the present study, entrainment, saltation characteristics and transport rates were examined at nine experimental sites ranging in elevation from ?154 m below sea‐level (Aiding Lake) to 5076 m above sea‐level (Tanggula Mountain pass on the Qinghai–Tibetan plateau). At each site, a portable wind tunnel and high‐speed camera system were set up, and the friction wind velocity, threshold friction velocity and sand flow structure were observed systematically. For a given volumetric airflow, lower air density increases the wind velocity. Low air density also creates a high threshold friction velocity. The Bagnold wind erosion threshold model remains valid, but the value of empirical parameter A decreased with decreasing air density and ranged from 0·10 to 0·07, the smallest values reported in the literature. For a given wind velocity, increased altitude reduced total sand transport and creeping, but the saltation rate and saltation height increased. The present results provide insights into the fundamental mechanisms of the initiation and transport of sand by wind in regions with an extreme temperature or altitude (for example, alpine deserts and low‐lying lake basins) or on other planets, including Mars. These results also provide theoretical support for improved sand‐control engineering measures. The data and empirical equations provided in this paper improve the ability to estimate threshold and transport conditions for wind‐blown sand. 相似文献
18.
The effect of surface moisture on the entrainment of dune sand by wind: an evaluation of selected models 总被引：5，自引：0，他引：5
Abstract Reliable predictions of wind erosion depend on the accuracy of determining whether erosion occurs or not. Among the several factors that govern the initiation of soil movement by wind, surface moisture is one of the most significant. Some widely used models that predict the threshold shear velocity for particle detachment of wet soils by wind were critically reviewed and evaluated. Wind‐tunnel experiments were conducted on pre‐wetted dune sand with moisture contents ranging from 0·00 to 0·04 kg kg?1. Sand samples were exposed to different wind speeds for 2 min. Moisture content was determined gravimetrically before and after each experiment, and the saltation of sand particles was recorded electronically with a saltiphone. Shear velocities were deduced from the wind speed profiles. For each moisture content, the experiments were repeated at different shear velocities, with the threshold shear velocity being determined by least‐squares analysis of the relationships between particle number rates and shear velocity. Within the 2‐min test runs, temporal changes in particle number rates and moisture contents were detected. A steep increase in the threshold shear velocity with moisture content was observed. When comparing the models, large differences between the predicted results became apparent. At a moisture content of 0·007 kg kg?1, which is half the moisture content retained to the soil matrix at a water tension (or matric potential) of ?1·5 MPa, the increase in ‘wet’ threshold shear velocity predicted with the different models relative to the dry threshold shear velocity ranged from 117% to 171%. The highest care should therefore be taken when using current models to predict the threshold shear velocity of wet sediment. Nevertheless, the models of Chepil (1956; Proc. Soil Sci. Soc. Am., 20, 288–292) and Saleh & Fryrear (1995; Soil Sci., 160, 304–309) are the best alternatives available. 相似文献
19.
Development of deflation lag surfaces 总被引：3，自引：0，他引：3
A series of wind tunnel tests were carried out to investigate the development of deflation lags in relation to the non-erodible roughness element concentration. Glass spheres (18 mm in diameter) were placed along the complete length of the wind tunnel working section in regular staggered arrays using three different spacings (d=18, 30 and 60 mm) and completely covered with a 0.27-mm erodible sand. A pre-selected free stream velocity above threshold (8m s?1) was established above the surface and the sediment transport measured at 2-s intervals using a wedge-shaped trap in which an electronic balance is incorporated. Throughout each test, the emerging lag surface was periodically photographed from above at two locations upwind of the trap. The photographs were electronically scanned and analysed to calculate the lag element coverage and location, as well as mean height and frontal area for each time period. Test results indicate that lag development has a profound effect on both the sediment flux and wind profile characteristics. Initially, there is an increase in sediment flux above that for a rippled sand bed because of increased erosion around and reduced kinetic energy loss in highly elastic collisions with the emerging roughness elements. With further emergence, a dynamic threshold is reached whereupon the sediment flux decreases rapidly, tending towards zero. At this point, the supply of grains to the air stream through fluid drag follows a reduction in aerodynamic roughness and, therefore, surface shearing stress. At least as important is the lesser potential for grain ejection at impact because of reduced momentum imparted from the air stream during saltation. Although recent shear stress partitioning models indicate when particle movement may commence on varying surfaces, our experimental results demonstrate that this partitioning has a further direct bearing upon the saltation flux ratio. 相似文献
20.
Wind tunnel test of snow loads on a stepped flat roof using different granular materials 总被引：1，自引：0，他引：1
An accurate prediction of wind-induced redistribution of snow load on roof surfaces is vital to structural design. To represent the pattern of snow distribution caused by snowdrift in wind tunnel test, appropriate modeling particles should be selected. The particle density is the key to determine the values of several important similarity parameters. In this study, the redistribution of snow load on a stepped flat roof was simulated by means of wind tunnel test using low-density saw wood ash, medium-density polyfoam, and high-density silica sand, respectively. To ensure the comparability of the test results of the three modeling particles, the wind tunnel test results for comparison were performed under almost the same conditions of dimensionless wind velocity and dimensionless time. Then, the results of the present study were compared with those from field observations of prototypes in previous studies. The effects of wind duration, wind velocity, and roof span on the redistribution of snow on roof surfaces were investigated. The characteristics of erosion/deposition range and the location of maximum quantities of erosion/deposition under independent effects of wind duration, wind velocity, and roof span were also studied. 相似文献