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1.
Chanwen JIANG 《干旱区科学》2017,9(5):727-742
Velocity is a key parameter characterizing the movement of saltating particles. High-speed photography is an efficient method to record the velocity. But, manually determining the relevant information from these photographs is quite laborious. However, particle tracking velocimetry(PTV) can be used to measure the instantaneous velocity in fluids using tracer particles. The tracer particles have three basic features in fluids: similar movement patterns within a small region, a uniform particle distribution, and high particle density. Unfortunately, the saltation of sand particles in air is a stochastic process, and PTV has not yet been able to accurately determine the velocity field in a cloud of blowing sand. The aim of the present study was to develop an improved PTV technique to measure the downwind(horizontal) and vertical velocities of saltating sand. To demonstrate the feasibility of this new technique, we used it to investigate two-dimensional saltation of particles above a loose sand surface in a wind tunnel. We analyzed the properties of the saltating particles, including the probability distribution of particle velocity, variations in the mean velocity as a function of height, and particle turbulence. By automating much of the analysis, the improved PTV method can satisfy the requirement for a large sample size and can measure the velocity field of blowing sand more accurately than previously-used techniques. The results shed new light on the complicated mechanisms involved in sand saltation. 相似文献
2.
Many desert expressways are affected by the deposition of the wind-blown sand,which might block the movement of vehicles or cause accidents.W-beam central guardrails,which are used to improve the safety of desert expressways,are thought to influence the deposition of the wind-blown sand,but this has yet not to be studied adequately.To address this issue,we conducted a wind tunnel test to simulate and explore how the W-beam central guardrails affect the airflow,the wind-blown sand flux and the deposition of the wind-blown sand on desert expressways in sandy regions.The subgrade model is 3.5 cm high and 80.0 cm wide,with a bank slope ratio of 1:3.The W-beam central guardrails model is 3.7 cm high,which included a 1.4-cm-high W-beam and a 2.3-cm-high stand column.The wind velocity was measured by using pitot-static tubes placed at nine different heights(1,2,3,5,7,10,15,30 and 50 cm)above the floor of the chamber.The vertical distribution of the wind-blown sand flux in the wind tunnel was measured by using the sand sampler,which was sectioned into 20 intervals.In addition,we measured the wind-blown sand flux in the field at K50 of the Bachu-Shache desert expressway in the Taklimakan Desert on 11 May 2016,by using a customized 78-cm-high gradient sand sampler for the sand flux structure test.Obstruction by the subgrade leads to the formation of two weak wind zones located at the foot of the windward slope and at the leeward slope of the subgrade,and the wind velocity on the leeward side weakens significantly.The W-beam central guardrails decrease the leeward wind velocity,whereas the velocity increases through the bottom gaps and over the top of the W-beam central guardrails.The vertical distribution of the wind-blown sand flux measured by wind tunnel follows neither a power-law nor an exponential function when affected by either the subgrade or the W-beam central guardrails.At 0.0H and 0.5H(where H=3.5 cm,which is the height of the subgrade),the sand transport is less at the 3 cm height from the subgrade surface than at the 1 and 5 cm heights as a result of obstruction by the W-beam central guardrails,and the maximum sand transportation occurs at the 5 cm height affected by the subgrade surface.The average saltation height in the presence of the W-beam central guardrails is greater than the subgrade height.The field test shows that the sand deposits on the overtaking lane leeward of the W-beam central guardrails and that the thickness of the deposited sand is determined by the difference in the sand mass transported between the inlet and outlet points,which is consistent with the position of the minimum wind velocity in the wind tunnel test.The results of this study could help us to understand the hazards of the wind-blown sand onto subgrade with the W-beam central guardrails. 相似文献
3.
文中基于光滑粒子流体动力学(Smoothed Particle Hydrodynamics:SPH)方法,采用五次样条光滑函数,通过调节不同类型粒子光滑因子,对风沙流运动特性进行分析:1)在风沙流起动阶段,沙粒平均水平速度随高度增加而增大,同一高度处沙粒平均水平速度随时间推移而减小。2)风沙流稳定前后,沙粒数均随高度的增加而减少。3)风沙流形成过程中气体粒子在计算域中心位置产生涡流,并随着时间推移,涡流又出现在计算域中上及右下方位置。4)起沙前后气体脉动强度随摩阻风速增加而增加,随高度增加呈现不同变化。结果表明:该方法模拟精度较高,适用于解决风沙两相流数值模拟问题。 相似文献
4.
土壤风蚀量随残茬高度的变化规律研究 总被引：7，自引：1，他引：7
在内蒙古自治区武川县建立农田土壤风蚀试验区,采用内蒙古农业大学研制的移动式风蚀风洞和旋风分离式集沙仪,直接在农田上观测不同残茬高度条件下的农田风蚀土壤损失情况。试验结果表明:土壤风蚀量和扬起沙尘的高度随风速的增加而增加,随着作物秸秆残茬高度的增加而降低,且输沙量与高度变化符合指数函数关系,土壤颗粒主要集中在近地表层内运动。保护性耕作可明显地提高启沙风速,减少农田土壤损失,当秸秆高度为30 cm时,风蚀量仅为传统耕地的1/4左右。 相似文献
5.
风沙侵袭影响下绿洲边缘植物群落点格局分析 总被引：3，自引：0，他引：3
以塔克拉玛干沙漠南缘策勒绿洲为研究区,运用Ripley’s K(t)函数点格局分析,研究风沙侵袭影响下植物群落结构和点分布格局的变化。风沙侵袭对植物组成种类无影响,均由骆驼刺、柽柳和花花柴组成,但自内侧向外围随着风沙侵袭强度加大,植株密度和盖度会明显降低,组成比例上从以骆驼刺为主向各种群均匀发展,并且骆驼刺的树冠面积随之显著增加,柽柳和花花柴的树冠面积显著减小。种群分布格局具有明显的尺度依赖性,3个种群在30 m的空间尺度上均以聚集分布为主,随风沙掩埋强度增加,3个种群分布类型从聚集变为随机,且聚集分布的尺度范围及聚集峰值所在尺度逐渐减小。研究区内各种群间以负关联为主,随风沙侵袭强度加大,各种群间的负关联程度及尺度范围均呈减弱趋势,最终变为不关联或部分尺度上较弱负关联。风沙掩埋的直接干扰和植物适应性及种间关联关系是种群空间格局变化的主要原因,强烈的风沙掩埋抑制了植物的生长和繁殖,促使群落退化,所以绿洲边缘的流沙深入区是过渡带建设及保护的重点区域。 相似文献
6.
植被沙障对近地表风沙流特征影响的风洞实验 总被引：4，自引：1，他引：3
植被沙障在一些地区已成为沙害防治的有效手段,其应用也越来越广泛,但对其治沙机理尚不很清楚.在盖度为10%,15%,20%,30%,40%,60%情况下,对植被沙障的防风固沙效益进行了风洞试验.实验风速设置为6,8,11 m/s,测定不同植被盖度的风速廓线特征、风沙流结构特征及其防沙效果.实验结果表明:①积沙总量随盖度增加而逐渐降低,风沙流中的砂粒分布在一定的高度范围内,但分布的高度随盖度的增加呈下降趋势;②植株的茂密程度对风沙流的结构有明显影响,盖度越高,积沙量越集中在下部;③盖度并不是导致积沙量为零的唯一指标,风蚀是否发生,还与植被的疏透度、防护林的高度等有关. 相似文献
7.
在内蒙古自治区武川县建立农田土壤风蚀试验区,采用内蒙古农业大学研制的移动式风蚀风洞和旋风分离式集沙仪,观测不同残茬高度条件下农田土壤的风蚀情况.试验结果表明:土壤风蚀量和扬起沙尘的高度随风速的增加而增加,随着作物秸秆残茬高度的增加而降低,且风蚀量与高度变化符合指数函数关系,土壤颗粒主要集中在近地表层内运动.保护性耕作可明显地提高起沙风速,减少农田土壤损失,当秸秆高度为30 cm时,风蚀量仅为传统耕地的1/4左右. 相似文献
8.
塔克拉玛干沙漠北缘荒漠过渡带风沙流结构特征分析 总被引：1，自引：0，他引：1
利用多种集沙仪,通过野外实时输沙观测,对塔克拉玛干沙漠北缘荒漠过渡带的地表风沙流特征进行了分析,结果表明：① 100 cm高度范围内,总输沙量的47.3%分布在30 cm高度内,这一比例小于前人的研究结果;输沙量随高度的变化比较符合幂函数分布。② 风沙流输沙的粒径以细砂、极细砂与粉砂为主,各高度层所占比例均达99%以上;风沙流输沙平均粒径随高度增加而减小,沙尘的含量随高度增加呈现“象鼻”状分布。③ 风沙流中贴地层风速廓线受风沙相互作用的影响,不再符合对数分布,更加符合幂函数u=azb分布。 相似文献
9.
南疆铁路风沙流结构特征研究 总被引：2，自引：0，他引：2
通过对南疆铁路戈壁风沙流进行现场观测研究,提出了关于风沙流密度的计算方法,将大风所携沙粒定量化,解决了风沙运动研究中如何利用现场定时观测研究风沙流动态变化的技术难题.根据现场实测资料分析,揭示了南疆铁路风沙流密度随高度和风速的变化关系.从中可以看出,风沙流密度随高度变化显现斜"L"形,以3m高为分界点;而相对的风沙流密... 相似文献
10.
Guardrail, an important highway traffic safety facility, is mainly used to prevent vehicles from accidentally driving off the road and to ensure driving safety. Desert highway guardrails hinder the movement of wind-blown sand, resulting in the decline of sand transportation by the pavement and the deposition of sand gains on the pavement, and endangering traffic safety. To reveal the influence of guardrails on sand transportation of desert highway pavement, we tested the flow field and sand transport volume distribution around the concrete, W-beam, and cable guardrails under different wind velocities through wind tunnel simulation. Wind velocity attenuation coefficients, sand transportation quantity, and sand transportation efficiency are used to measure sand transportation of highway pavement. The results show that the sand transportation of highway pavement was closely related to the zoning characteristics of flow field and variation of wind velocity around the guardrails. The flow field of the concrete guardrail was divided into deceleration, acceleration, and vortex zones. The interaction between the W-beam guardrail and wind-blown sand was similar to that of lower wind deflector. Behind and under the plates, there were the vortex zone and acceleration zone, respectively. The acceleration zone was conducive to transporting sand on the pavement. The cable guardrail only caused wind velocity variability within the height range of guardrail, and there was no sand deposition on the highway pavement. When the cable, W-beam, and concrete guardrails were used, the total transportation quantities on the highway pavement were 423.53, 415.74, and 136.53 g/min, respectively, and sand transportation efficiencies were 99.31%, 91.25%, and 12.84%, respectively. From the perspective of effective sand transportation on the pavement, the cable guardrail should be preferred as a desert highway guardrail, followed by the W-beam guardrail, and the concrete guardrail is unsuitable. The study results provide theoretical basis for the optimal design of desert highway guardrails and the prevention of wind-blown sand disasters on the highway pavement. 相似文献
11.
利用2014年7月至8月塔中地区沙尘与扬沙天气下风沙流运动的实测数据,对0~85 mm高度内风沙流运动进行了研究。结果表明:(1)0~85 mm高度层,输沙率(Q)随风速(v)增大呈幂函数规律增加,R2≥0.975 7,且输沙率主要集中在0~35 mm高度内。(2)总输沙率和撞击颗粒数的最佳拟合函数为线性函数,R2≥0.878 2,相关性较好;塔中地区1 min最小临界起沙风速为4.0 m·s-1。(3)跃移运动集中在10:00—20:00,总输沙率最大值出现在12:00—16:00,17:00以后输沙率明显下降。 相似文献
12.
Fetch effect on the developmental process of aeolian sand transport in a wind tunnel 总被引：1，自引：0，他引：1
CHEN Zongyan 《干旱区科学》2020,12(3):436-446
As the sand mass flux increases from zero at the leading edge of a saltating surface to the equilibrium mass flux at the critical fetch length, the wind flow is modified and then the relative contribution of aerodynamic and bombardment entrainment is changed. In the end the velocity, trajectory and mass flux profile will vary simultaneously. But how the transportation of different sand size groups varies with fetch distance is still unclear. Wind tunnel experiments were conducted to investigate the fetch effect on mass flux and its distribution with height of the total sand and each size group in transportation. The mass flux was measured at six fetch length locations(0.5, 1.2, 1.9, 2.6, 3.4 and 4.1 m) and at three free-stream wind velocities(8.8, 12.2 and 14.5 m/s). The results reveal that the total mass flux and the mass flux of each size group with height can be expressed by q=aexp(–bh), where q is the sand mass flux at height h, and a and b are regression coefficients. The coefficient b represents the relative decay rate. Both the relative decay rates of total mass flux and each size group are independent of fetch length after a quick decay over a short fetch. This is much shorter than that of mass flux. The equilibrium of the relative decay rate cannot be regarded as an equilibrium mass flux profile for aeolian sand transport. The mass fluxes of 176.0, 209.3 and 148.0 μm size groups increase more quickly than that of other size groups, which indicates strong size-selection of grains exists along the fetch length. The maximal size group in mass flux(176.0 μm) is smaller than the maximal size group of the bed grains(209.3 μm). The relative contribution of each size group to the total mass flux is not monotonically decreasing with grain size due to the lift-off of some small grains being reduced due to the protection by large grains. The results indicate that there are complex interactions among different size groups in the developmental process of aeolian sand transport and more attention should be focused on the fetch effect because it has different influences on the total mass flux, the mass flux profile and its relative decay rate. 相似文献
13.
青藏铁路沱沱河路段流场特征及沙害形成机理 总被引：2，自引：0，他引：2
通过对青藏铁路沱沱河路段路基流场结构、风速廓线特征的风洞模拟实验研究,发现气流在途经铁路路基时,路基断面对近地表流场改变极大,在其两侧形成明显的遇阻抬升区、集流加速区、减速沉降区以及消散恢复区。铁路沙害的形成主要是路基迎风侧气流由于遇阻抬升和集流加速,对路肩和路基中上部产生风蚀;随着气流加速抬升,底层砂粒以跌落沉降的方式堆积在路基迎风坡坡脚,造成路基沙埋;当气流越过路基,在背风侧由于减速沉降和涡旋运动,风沙流处于过饱和状态,将所携带的大量砂粒堆积在背风坡。 相似文献
14.
Wind tunnel test on the effect of metal net fences on sand flux in a Gobi Desert,China 总被引：2，自引：0，他引：2
The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions: no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m(i.e., 13 H, where H denotes the fence height) downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through. 相似文献
15.
Yang ZHANG 《干旱区科学》2019,11(5):664-673
Windblown sand transport is a leading factor in the geophysical evolution of arid and semi-arid regions. The evolution speed is usually indicated by the sand transport rate that is a function of launch velocity of sand particle, whichhasbeen investigated by the experimental measurement and numerical simulation. However, the obtained results in literatures are inconsistent. Some researchers have discovered a relation between average launch velocity and wind shear velocity, while some other researchers have suggested that average launch velocity is independent of wind shear velocity. The inconsistence of launch velocity leads to a controversy in the scaling law of the sand transport rate in the windblown case. On the contrary, in subaqueous case, the scaling law of the sand transport rate has been widely accepted as a cubic function of fluid shear velocity. In order to explain the debates surrounding the windblown case and the difference between windblown and subaquatic cases, this study reinvestigates the scaling law of the vertical launch velocity of windblown transported sand particles by using a dimensional analysis in consideration of the compatibility of the characteristic time of sand particle motion and that of air flow. Then a wind tunnel experiment is conducted to confirm the revisited scaling law, where the sand particle motion pictures are recorded by a high-speed camera and then the launch velocity is solved by the particle tracking velocimetry. By incorporating the results of dimensional analysis and wind tunnel experiment, it can be concluded that, the ratio of saltonsnumber to reptonsnumberdetermines the scaling law of sand particle launch velocity and that of sand transport rate, and using this ratio is able to explain the discrepancies among the classical models of steady sand transport. Moreover, the resulting scaling law can explain the sand sieving phenomenon: a greater fraction of large grains is observed as the distance to the wind tunnel entrance becomes larger. 相似文献
16.
风沙流研究的历史、现状及其趋势 总被引：32，自引：1，他引：31
本文扼要回顾了风沙流的研究历史;简明评述了颗粒运动特征、风沙流结构、输沙率模型、起沙风模型、表面气流变化、风沙两相流等研究现状内容;就目前研究中存在的问题、研究趋势等方面作了探讨。 相似文献
17.
18.
基于二维Gumbel分布的降雨径流频率分析模型及其应用 总被引：2，自引：1，他引：1
本文探讨了二维Gumbel分布模型,给出了其经验频率和理论频率的计算方法,并建立了其联合重现期和条件重现期的分布模型。它可以给出不同程度暴雨和径流遭遇组合的频率,也可以在一定的降雨量条件下给出不同径流量的发生频率,或一定的径流量条件下给出不同降雨量的发生频率。这对于解决与风险有关的多因素影响下的水文计算问题是非常有用的。并以滹沱河流域岗南水库的入库年径流和年降雨量为例,分析了该模型的实用性,结果表明采用二维Gumbel分布模型来描述水文随机变量的联合分布是有效的。 相似文献
19.
土壤风蚀量随风速的变化规律研究 总被引：16，自引：1，他引：16
使用野外风洞作为风蚀研究的试验手段,通过农田土壤、沙及生土的风洞试验研究发现,农田土壤的风蚀量随风速呈指数函数变化,沙及生土的风蚀量随风速呈幂函数变化。试验研究还表明,农田土壤的风蚀量与表土层(3cm)的含水量呈显著负相关,沙的风蚀量与含水量的相关性不显著。风蚀导致土壤中的细颗粒成分大量损失,这是土壤颗粒粗化的原因所在。 相似文献
20.
Sediment transport of sand particles by wind is one of the main processes leading todesertification in arid regions, which severely impairs the ability of mankind to produce and live by driftingsand into settlements. Optimization designs of artificial facilities have lately attracted extensive interest forhuman settlement systems in deserts because of their acceptable protection effect, convenience ofimplementation, and low material cost. However, the complexity of a settlement system poses challengesconcerning finding suitable materials, artificial facilities, and optimization designs for sand depositionprotection. In an effort to overcome these challenges, we propose a settlement system built with brick, solarpanel, and building arrays to meet the basic needs of human settlements in arid regions while preventingwind-sand disasters. The wind flow and movement characteristics of sand particles in the brick, panel, andbuilding arrays were calculated using computational fluid dynamics and discrete phase model. Theperformance of three types of arrays in wind-sand flow in terms of decreasing the wind velocity and sandparticleinvasion distance was evaluated. The results show that the wind velocity near the surface and thesand invasion distance were significantly decreased in the space between the brick arrays through properlyselected vertical size and interspaces, indicating that the brick arrays have an impressive sand fixing andblocking performance;their effective protection distance was 3–4 m. The building arrays increased the nearsurfacewind velocity among buildings, resulting in less deposition of sand particles. The solar panel arrayswere similar to the building arrays in most cases, but the deposition of sand particles on solar panels exerteda negative effect on energy utilization efficiency. Therefore, taking the optimal configuration of thesettlement system into consideration, this study concludes that (1) brick arrays, which were proven effectivein preventing sand particles, must be arranged in an upwind area;(2) solar panel arrays could accelerate thewind flow, so they are best to be arranged at the place where sand particles deposited easily;and (3) buildingarrays present a better arrangement in downwind areas. 相似文献