塔克拉玛干沙漠南缘风沙跃移运动研究——以策勒为例   总被引：3，自引：0，他引：3  

杨兴华  何清  霍文  艾力·买买提明  刘新春 《中国沙漠》2012,32(4):910-914

 利用Sensit传感器、BSNE集沙仪、全方位跃移集沙仪结合2 m气象塔,于2010年7月5日至8月24日在策勒绿洲-荒漠过渡带开展了风沙跃移运动强化观测试验,分析了该区域风沙跃移运动的部分特征。结果表明:①试验点2 m高度临界跃移起动1 h平均风速为5.0 m·s-1;跃移颗粒数与风速呈现较好的幂函数关系;②跃移输沙量的方向分布以偏西方向为主,主要集中在SW、WSW、W、WNW、NW5个方位,共计占到80.9%;③跃移运动在一日之内的任何时间段都可能发生,发生频率较高的时段集中在白天的11:00—19:00;④观测期间0～40 cm高度范围的跃移输沙通量为199.4 kg·m-1。  相似文献   

Height profile of the mean velocity of an aeolian saltating cloud: Wind tunnel measurements by Particle Image Velocimetry   总被引：3，自引：0，他引：3  

Ping Yang  Zhibao Dong  Guangqiang Qian  Wanyin Luo  Hongtao Wang 《Geomorphology》2007,89(3-4):320-334

The velocity of saltating particles is an important parameter in studying the aeolian sand movement. We used Particle Image Velocimetry to measure the variation with height of the mean particle velocity of a saltating cloud over a loose sand surface in a wind tunnel. The results suggest that both the horizontal and vertical particle velocities fit the Gaussian distribution well, and that the mean particle velocity of a saltating cloud varies with wind velocity, particle size and the height above bed. The mean horizontal velocity is mainly the result of acceleration by the wind and increases with an increase in friction wind velocity but decreases with an increase in grain size because greater wind velocity causes more acceleration and finer particles are more easily accelerated at a given wind velocity. It also increases with an increase in height by a power function, in agreement with previous results obtained by other methods such as the high-speed multi-flash photographic method and Particle Dynamics Analyzer (PDA), reflecting, first, the increase in wind velocity with height through the boundary layer, and second, the longer trajectory-particle path length increases with height and affords a longer time for acceleration by the wind. An empirical model relating the mean horizontal particle velocity and height, friction wind velocity as well as particle size is developed. The ratio of the mean horizontal particle velocity to the clean wind velocity at the same height increases with height but decreases with grain size. The magnitude of mean vertical velocity is much less (one or two orders less) compared with the mean horizontal velocity. The average movement in the vertical direction of a saltating cloud is upward (the mean vertical velocity is positive). Although the upward velocity of a saltating particle should decrease with height due to gravity the mean vertical (upward) velocity (the average of both ascending and descending particles) generally shows a tendency to increase with height. It seems that at higher elevations the data are more and more dominated by the ‘high-flyers’. The underlying mechanism for the mean vertical velocity distribution patterns needs to be clarified by further study.  相似文献   

On the rate of aeolian sand transport   总被引：3，自引：0，他引：3  

Michael Srensen 《Geomorphology》2004,59(1-4):53

A simple explicit formula for the transport rate of windblown sand is derived based on physical reasoning. The curve relating the dimensionless transport rate to the dimensionless friction speed exhibits the empirically well-established peak. In fact, the theory developed in the paper can explain the peaked shape of this curve. Three empirically determined coefficients in the formula can be given a physical interpretation. The formula is shown to fit transport rates measured in wind-tunnel experiments well, except for very coarse sand. Formulae for the wind profile in the saltation layer and for the grain dislodgement rate in dependence on the friction speed are obtained as part of the theory.  相似文献   

Development of the saltation system under controlled environmental conditions     

Samantha Arnold 《地球表面变化过程与地形》2002,27(8):817-829

The transport of sand by the wind occurs predominantly by the process of saltation. Following the entrainment of sand by an above threshold wind, the saltation system is regulated by the mutual interaction of the atmospheric boundary‐layer, the sand cloud and the sand bed. Despite existing data on the spatial and temporal development of the sand transport system, very little is known about the development of the saltation system towards equilibrium. Results are presented from wind‐tunnel experiments that were designed to address the simultaneous spatial and temporal development of the saltation system, with and without artificial sand feed. The development of the saltation system was monitored over a streamwise length of 8 m during a period of 3600 s. Mass flux data were measured simultaneously at 1 m intervals by the downwind deployment of seven Aarhus sand traps. Wind velocity data were collected throughout the experiments. The downwind spatial development of the saltation system is manifested by an overshoot in mass flux and friction velocity prior to declining towards a quasi‐equilibrium. Mass flux overshoots at approximately 4 m downwind, in remarkable agreement with existing data of a comparable scale. Friction velocity overshoots at approximately 6 m downwind, a result not previously witnessed in saltation studies. The overshoot of mass flux prior to the overshoot in friction velocity is a spatial manifestation of the time lag between the entrainment of grains and the deceleration of the wind by the grains in transport. Temporally, the development of the saltation system is controlled by the availability of entrainable grains from the sand bed. Through time the saltation system develops from a transport‐limited to a supply‐limited system. The depletion of the sand bed through time limits the appropriateness of the assumption of ‘equilibrium’ for the universal prediction of mass flux. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

The emission and vertical flux of particulate matter <10 μm from a disturbed clay-crusted surface     

Christopher A. Houser  & William G. Nickling 《Sedimentology》2001,48(2):255-267

Arid and semi‐arid environments are important sources for the atmospheric loading of PM₁₀ (particulate matter <10 μm), although the emission of this material is often limited by surface crusts. This study investigates the emission and vertical flux of PM₁₀ from a clay‐crusted playa, with and without saltating grains to abrade the surface. Using a portable field wind tunnel, it was found that, despite disturbance to the surface, the emission of PM₁₀ decays rapidly without abrasion. Only in the presence of saltating grains was PM₁₀ continuously liberated from the surface, such that the emission rate (the total amount of PM₁₀ emitted from the surface expressed as a horizontal flux) varied linearly with the saltation transport rate. Although the emission of PM₁₀ was found to depend on saltation abrasion, past studies have tended to focus on the relationship between the vertical flux of PM₁₀ (the amount of PM₁₀ being transported vertically through the boundary layer) and the shear velocity. In this study, the vertical flux of PM₁₀ was found to vary with the shear velocity to the power of 2·14. Although the vertical PM₁₀ flux is a proportion of the emission rate (the horizontal flux), no statistically significant relationship was observed between the emission rate and the shear velocity. The disparity of these results is explained by the lack of a consistent relationship between the shear velocity and the saltation transport rate in this supply‐limited environment. This suggests that the observed relationship between the vertical PM₁₀ flux and the shear velocity is a spurious correlation, resulting from the use of shear velocity to calculate the vertical dust flux. It is thus concluded that shear velocity is not an appropriate variable for emission modelling in supply‐limited environments and that improvements in dust emission modelling will only be realized if the abrasion process is the focus of a concerted research effort.  相似文献   

兰新高铁烟墩风区戈壁近地表风沙流跃移质垂直分布特性     

谭立海  张伟民  边凯  安志山  牛百成  高扬 《中国沙漠》2018,38(5):919-927

跃移质作为风沙流的主体,其近地表垂直分布规律是风沙物理学的重要研究内容,对防沙工程具有重要的指导意义。受研究条件与观测仪器限制,戈壁特别是极端大风区近地表风沙流结构特性研究较为薄弱。利用多梯度风蚀传感器与阶梯式集沙仪对兰新高铁烟墩风区戈壁近地表风沙流跃移质的垂直分布特性进行了观测研究。结果表明：兰新高铁烟墩风区戈壁沙粒发生跃移运动的2 m高临界风速达12 m·s^-1;戈壁近地表风沙流具有明显的阵性特征,沙粒跃移发生的时间比例在50%以下,与平均风速成正相关关系,与风速脉动强度无显著相关关系;2 m高阵风7级风速下,戈壁跃移沙粒主要集中于地表50 cm范围内,近地表风沙流结构呈"象鼻效应",跃移质最大质量通量出现在地表2.5~5 cm高度处,沙粒最大跃移高度可达2 m,且沙粒跃移高度随2 m高风速的增加呈指数规律递增。因此,兰新高铁烟墩风区2 m高阻沙栅栏不足以完全阻截戈壁风沙流,是造成烟墩风区兰新高铁轨道积沙的重要原因之一。  相似文献   

Wind tunnel Study on Aeolian Saltation Dynamics and Mass flow   总被引：1，自引：0，他引：1  

Remigius Egwuonwu Okoli 《Journal of Arid Environments》2003,53(4):569-583

Aeolian saltation dynamics and mass flows were studied in a wind tunnel. Evaluation of the measured flux rates suggested a new sand transport equation. The theoretical rate data of this equation fitted well with the measured flux rates, as well as with those predicted by other equations reported in literature. Also, an expression was established that predicted accurately the observed roughness heights as well as the roughness data reported in Bagnold (1941). Similarly, the grain-borne drag expression was developed and used to establish the height above the surface at which the grain-borne drag is at equilibrium with the aerodynamic traction.  相似文献   

Characterizing the height profile of the flux of wind-eroded sediment   总被引：4，自引：0，他引：4  

Zhibao Dong  Guangqiang Qian 《Environmental Geology》2007,51(5):835-845

Wind erosion causes severe environmental problems, such as aeolian desertification and dust storms, in arid and semiarid regions. Reliable prediction of the height profile of the wind-eroded sediment flux is crucial for estimation of transport rates, verification of computer models, understanding of particle-modified wind flows, and control of drifting sand. This study defined the basic height profile for the flux of wind-eroded sediment and the coefficients that characterize its equation. Nine grain-size populations of natural sand at different wind velocities were tested in a wind tunnel to measure the flux of sediment at different heights. The resulting flux profiles resemble a golf club with a small back-turn where the flux increases with increasing height within 20 mm above the surface. If the small back-turns are neglected, the flux profiles can be expressed by an exponential-decay function where q _r(z) is the dimensionless relative flux of sediment at height z, which follows the exponential-decay law proposed by previous researchers for aeolian saltation. Three coefficients (a creep proportion, a relative decay rate, and an average saltation height) are proposed to characterize the height profile. Coefficients a and b in the above equation represent the creep proportion and relative decay rate as a function of height, respectively. Coefficient a varies widely, depending on grain size and wind velocity, but averages 0.09. It is suggested that the grain size and wind velocity must be specified when discussing creep proportion. Coefficients a and b are nearly linearly correlated and decrease as grain size and wind velocity increase. The average saltation height (the average height sediment particles can reach) was a function of grain size and wind velocity, and was well correlated with coefficients a and b.  相似文献   

冲击起沙的概念模型     

赵建华  张强  隆霄 《中国沙漠》2012,32(2):323-330

冲击起沙是最重要的起沙方式。鉴于Lu和Shao提出的体积模型的不足,通过分析沙床受到冲击后应力的传递规律,类比于电子的跃迁模型,提出了冲击起沙的跃迁模型来解决冲击起沙问题。该模型的基本思想是,沙粒冲击沙床时,能量会沿冲击点向周围粒子扩散,当某一粒子获得的能量大于跃出所需要的能量时,该粒子即从床面跃出;多余的能量将转化为该粒子的跃出初动能。冲击起沙问题由此变成了一个研究跃出能量的大小和能量传输规律的问题。根据该模型,基于能量传输的吸收系数法和传输方程近似法,给出了两维和三维情形下冲击起沙释放的粒子数、速度分布和冲击坑形状的表达式。两维情形下显示,冲击坑的大小与释放的粒子数和粒径大小正比,而且伴随着冲击坑的形成,可能会发生崩塌现象。吸收系数法显示,两维冲击坑随着吸收系数的增大是先增大,后反而出现了收缩。传输方程近似法显示,两维冲击坑的大小正比于kt。  相似文献   

影响拜格诺结的若干因素分析   总被引：7，自引：4，他引：3  

何丽红  武建军  郑晓静 《中国沙漠》2003,23(4):347-354

给出了全面描述风沙耦合作用下沙粒跃移运动的理论模型,利用数值方法对风沙耦合作用以及空气上升力、Magnus力、静电力等因素对沙粒跃移运动和风速廓线的影响进行了研究,从而揭示出拜格诺结(Bagnold's Kink)高度与其对应的风速及沙粒跃移高度的关系。  相似文献