Wind-blown Sand Movement Research Articles

The variation of particle concentration with height of wind-blown coral sand

Wind-blown coral sand movement is common in the marine coral sand island environment but received much less research attention compared to desert and coastal sands. We used the particle image velocimetry technique with wind tunnel experiments to determine the decay trends of the particle number density, nominal particle area density, and actual particle area density with height for wind-blown coral sands from the South China Sea. Then, a new morphology factor FM that consists of volume V, density ρs, drag coefficient CD, and projected area A of coral sands, was defined to evaluate the influences of particle characteristics on wind-blown sand movement and the results were compared with those of quartz sands from an inland desert. We found that the average FM of coral sands is more comparable to that of coarse quartz sands than smaller size groups. Coral sands tend to move nearer the surface during aeolian processes compared to smaller quartz ones due to their larger FM. The decay rate of particle number density of coral sands with height is similar to that of coarse (0.8–1 mm) quartz sands, but significantly larger than that of smaller quartz ones. The decay rate of the actual particle area density of coral sands with height is larger than that of their nominal particle area density, so that significant deviations may exist if a fixed particle size and spherical shape are assumed to study wind-blown particle movement. The present work contributes to understand the effect of particle characteristics on the wind-blown sand movement from a physical mechanism perspective for both desert quartz sands and marine coral sands.

Degradable cellulose acetate-based waterborne polyurethane sand-fixing agents for sand control in desert regions

In hot and arid desert regions, degradable chemical sand-fixing agents are efficient in dealing with problems caused by wind-blown sand movement without damaging the environment. This study aimed to develop a set of biodegradable sand-stabilizing substances, cellulose acetate (CA)-based waterborne polyurethane (WPU), utilizing CA as a partial hydroxyl provision through an acetone-based technique. The findings demonstrate that all the CA/WPU sand-fixing agents had unique, evenly spherical particles and were fully capable of degradation. The CA/WPU-2 sand-fixing agent contained 20 % polypropylene glycol (PPG) of CA. It showed strong viscosity, thermal stability, and water resistance. Furthermore, seed germination will be hindered by the CA/WPU-2 sand-fixing agent due to its superior sand-fixing capability compared to pure WPU. Consequently, it is suitable for application in arid regions where plant survival is difficult. CA/WPU-6 contained 120%PPG of CA. it showed outstanding O2 permeability and hydrophilicity due to its significant use of cellulose acetate. In addition, it demonstrated higher wind-blown sand resistance compared to popular commercial sand-fixation production. Furthermore, it sustained a consolidation strength lower than the highest penetration capability for herbaceous plant seeds. Therefore, CA/WPU-6 is a suitable option for establishing vegetation in dry situations. The results of this study address the demand for sustainable production and cost reduction, offering significant potential for industrial applications.

Spatial Characteristics of Aeolian Sand Transport Affected by Surface Vegetation along the Oshang Railway

Blown sand transport plays a pivotal role in determining the optimal placement of sand protection facilities along railways in sandy areas. Surface vegetation cover significantly influences blowing sand activities along the Oshang Railway (from Otog Front Banner to Shanghai-Temple Town). In this study, the spatial characteristics of aeolian sand transport along the railway were derived from field observations conducted at five different locations, each with varying fractional vegetation cover (FVC). The results indicate that sand-transport intensity does not fully correlate with the wind energy environment, primarily due to differences in surface vegetation cover among the observation sites. We utilize the dimensionless ratio Q·g·f/(0.136 × DP·ρa) to represent the sand transport rate (Q), the sand-moving wind frequency (f) and drift potential (DP), exhibiting a negative exponential trend with FVC. Sand transport is effectively restrained when FVC is greater than or equal to 20%. Conversely, when FVC is less than 20%, sand transport intensity exponentially increases with decreasing fractional vegetation cover. After careful analysis, we propose a simple empirical expression that incorporates the influence of both the wind field and fractional vegetation cover to assess sand transport on a flat surface. The study offers valuable insights for designing wind-blown sand protection measures along railways and evaluating wind-blown sand movement on a flat surface affected by vegetation.

An investigation of the effect of stratification stability and saltation sand flux on the anisotropy of atmospheric surface layer wall turbulence

In the atmospheric surface layer (ASL), the anisotropic characteristics of turbulence become more complex due to the strong influence of heat flux and particle motion. In this paper, the effects of stratification stability and total saltation sand flux on turbulent anisotropy of ASL wall turbulence are systematically analyzed by using high-frequency 3D velocity, temperature, and saltation sand flux measured in the field. Our results show that the temperature gradient intensifies the spanwise turbulent motion and enhances the vertical motion asymmetry. Although the buoyancy-driven turbulence enhances the spanwise variation, the momentum transfer mode between the streamwise–vertical and spanwise–vertical does not change. With the increase in instability, the large-scale motions (LSM) of the spanwise velocity may be destroyed and more spanwise small-scale motions (SSM) formed. In addition, saltation increases the sharpness, randomness, and extreme frequency of spanwise velocity distribution, but does not change the momentum transfer mode. Saltation may enlarge the fluctuation range and scale of the spanwise velocity, but may not be the main factor affecting the anisotropy of SSM. These results can deepen people's understanding of wind-blown sand movement and turbulence properties in ASL, and provides empirical data and insights that can significantly contribute to the development and refinement of turbulence models, particularly those that need to account for the complex interplay between stratification stability, saltation sand flux, and turbulence anisotropy.

Characteristics and interactions of fluctuation velocities, saltation mass flux, and temperature in the atmospheric surface layer

The essence of wind-blown sand movement is a particle movement system driven by high Reynolds number wall turbulence in the atmospheric surface layer (ASL). Understanding this phenomenon is crucial as the law and mechanism of sand movement have not been effectively revealed at present. In this study, we utilize the high-frequency time series data from the Oceano site, a renowned location for such studies, which includes streamwise wind velocity (u), wall-normal wind velocity (w), temperature (T), and total saltation mass flux (q) to delve deeper into wind-blown sand movement. The results indicate a positive correlation between T and w. Interestingly, this correlation not only escalates with height but also intensifies with the increase of the stratification stability parameters (z/L). Sand influences the intensity ratio of each quadrant to Reynolds stress without altering the time ratio. Both the ejection and sweep processes correlate well with z/L. Similarly, q also exhibits a good correlation with z/L. The buoyancy's impact on the low-frequency fluctuations of q might be through its effect on the low-frequency fluctuations of w, enhancing the sand transport capacity of w. This discovery holds profound implications for the study of two-phase flow in ASL and the precise prediction of surface sediment transport.

Erosion Model for Wind-Blown Sand Flow at Earthen Sites in Arid Environment, Northwest China

ABSTRACT This study investigates the erosive impact of wind-blown sand on earthen sites within arid environments through the establishment of meteorological observation equipment. Over a span of 47 months, a comprehensive approach encompassing numerical simulation, plume analysis, particle examination, three-dimensional scanning, and photo monitoring was employed to continuously monitor the patterns of wind-blown sand movement and the degradation of test walls. The study identifies six distinct zones extending from five times the windward side to ten times the leeward side of the test wall’s height. Notably, a negative correlation between captured particle mass and the height of the sand traps is observed, with 70% of particles concentrated within 50 cm from the base of the test wall. Three primary erosion mechanisms for wind-blown sand are elucidated, including frontal impact, side abrasion, and reverse sapping. Furthermore, the study highlights pronounced erosion at the base of the wall due to vortex flow, with depth erosion affecting the lower, side, and upper sections of the test walls. This paper delves into the erosion mechanisms and operational models of wind-blown sand flow surrounding discontinuous site walls, offering valuable insights for the conservation of ancient earthen sites.

Aeolian sediment transport over sandy gobi: Field studies in the Nanhu gobi along the Hami-Lop Nor Railway

Wind-blown sand over sandy gobi with an abundant sediment supply can cause severe sand hazards. However, compared with the study of aeolian transport over gravel gobi with a limited sediment supply, less attention has been devoted to sandy gobi, and thus, our understanding of wind-blown sand movement on sandy gobi is still poor. Here, we report the results of observations of three transport events on a sandy gobi along the Hami-Lop Nor Railway based on high-frequency saltation particle count and horizontal sediment flux measurements coupled with instantaneous wind velocity measurements. The results reveal that, unlike the notably intermittent aeolian saltation over gravel gobi, continuous transport occurred on the sandy gobi. The mean saltation layer height was 0.23 ± 0.07 m, and it was positively related to both the grain size of surface particles and the wind velocity regardless of the gobi type. The sediment transport rates could be expressed as the power function Q = ap/g[u∗ (u∗2-u∗t2)]b, and the scaling parameter (b) reached to 2.5, which is much larger than that of other gobi areas (b = 1). Our findings suggest that the wind-blown sand over sandy gobi is much more severe than that over gravel gobi, and the Nanhu sandy gobi is the major sand source for sand hazards of the Hami-Lop Nor Railway. Sand-fixation measures such as checkerboard sand barriers with enhanced checkerboard size and barrier height should be the main subject of sand control systems for the Hami-Lop Nor Railway in sandy gobi.

CFD evaluation of erosion rate around a bridge near a sand dune

This study performs a series of simulations through solving the Navier-Stokes equations and the RNG k-ε turbulence model to investigate the wind erosion rates around a bridge in a desert area with sand dunes. The digital elevation model of sand dunes and the bridge model are obtained respectively from hypsographic map and construction drawings. Through combining them into the CFD software of Fluent the simulation zone was formed. The data of wind speed obtained from field observation is fitted into a logarithm format, which was imported into Fluent model as a inlet wind speed condition. Then, the effect of Dun-Go railway on wind-blown sand movement of the neighbouring environment is simulated. The results exhibit that affected by both the sand dune and bridge, the flow field is in a complex condition. It is also shown that the bridge in upstream of the sand dune will not increase the sand transport rate intensively, but change both wind velocity gradient and turbulence kinetic energy over surface of sand dune. On the other hand, when the bridge is built downstream the sand dune, simulation results show that sand deposition rate would be decreased in reference region downstream the pier.

A numerical investigation into sand grain/slope bed collision

The impact of sand grain on sandy bed surface is not only one of the main processes of near-surface aeolian sand movement, but also the main cause of sand surface damage and soil erosion. In this study, we first simulate the process of grain-bed impact and splash of sand grains with different sizes on sand bed surface using the discrete element method. Then we analyze the relationships among the number, speed and angle of splashing grains and the speed and angle of the impacting sand grain with different slopes. Finally, we present the splash function of the takeoff speed and angle of splashing grains with the incident speed and angle changing and give their probability density distributions. This research is of great importance to understand the windblown sand movement on sand dune or ripples.

Sand transportation and reverse patterns over leeward face of sand dune

Sand saltation has complex interactions with turbulent flow and dune form. Most models of wind-blown sand consider ideal circumstances such as steady wind velocity and a flat surface, and the bulk of data on wind flow and sand transport over an individual dune has focused mostly on the influence of dune shape or inter-dune space on the wind flow, neglecting the effect of morphology on sand saltation, particularly airflow and sand transportation over the leeward slope. Wind flow structures over the leeward slope of sand dunes have a fundamental influence on the organization of sand dunes. In order to understand sand dune dynamics, lee face airflow and sediment transportation should be paid more attention. Previous field observations could not measure turbulent flow structure well because of the limited observation points and the influence of experiment structure on wind field. In addition, the reverse sand particles over leeward face could not be collected by sand trap in field. Numerous field observations could not measure turbulent flow structure because of the limited observation points and the influence of experimental structures on the wind field. In addition, the reverse transport of sand particles over leeward face could not be collected by sand traps in field. Therefore, this paper aims to investigate the turbulent flow structure and sand transport pattern over the leeward slope. A numerical model of sand saltation over slope terrain is constructed, which also considers the coupling effects between air flow and sand particles. The large eddy simulation method is used to model turbulent flow. Sand transport is simulated by tracking the trajectory of each sand particle. The results show that terrain significantly alters the turbulent air flow structure and wind-blown sand movement, especially over the leeward slope. Here, mass flux increases initially and then decreases with height in the reversed flow region in the direction of wind flow, and the mass flux decreases with height in the reversed direction. The height of 0.5H is the height of vortex core in the reversed flow region. The vortex core is a critical point in the flow region where few particles are transited. In the reversed region, the reversed mass flux of sand particles is 25% of the mass flux in the flow direction. This research may contribute to scientific understanding of the mechanisms of sand motion and wind flow over leeward of dune and it is likely to be significant in desertification control.

Influence of slope gradient on the behavior of saltating sand particles in a wind tunnel

Current theoretical and experimental studies of windblown sand movement are mostly conducted on flat sand surfaces. However, sand dunes, basic forms of desert landscapes, have slope gradients that greatly influence the transportation of sand particles. In this study, sand velocity on the windward and leeward slopes of barchans dunes was measured using a laser Phase Doppler Particle Analyzer in a wind tunnel. Our results measured from slope are quite different from existing data of flat surface. The average velocity of sand particles increased from bottom to top of the windward slope. And the particle velocity on leeward slope is not greatly impact by position and wind speed. Unlike exponential decay on flat bed, the lift-off angle on windward slope shows left-skewed distribution with a single peak, and the distribution of impact and lift-off angle on leeward slope are entirely different from those obtained on flat bed. On the leeward slope, impact and lift-off angle were affected remarkably by the position on the slope. On the leeward slope, the number of particles with wind direction horizontal velocity is basically the same as those of particles with headwind direction horizontal velocity. The vertical and horizontal turbulence intensity reached the maximum when the particles were located 20mm from the bed surface near the bottom of leeward slope; and the minimum at 60mm from the bed surface. Both vertical and horizontal turbulence intensity of particles increased with increasing wind velocity. The increase in the horizontal turbulence intensity was greater than the increase in the vertical turbulence intensity. The findings from this study would provide a better understanding of movement of blown sands over sand dunes and mechanism underlying the formation of sand dunes.

Analysis of wind-blown sand movement over transverse dunes.

Wind-blown sand movement often occurs in a very complicated desert environment where sand dunes and ripples are the basic forms. However, most current studies on the theoretic and numerical models of wind-blown sand movement only consider ideal conditions such as steady wind velocity, flat sand surface, etc. In fact, the windward slope gradient plays a great role in the lift-off and sand particle saltation. In this paper, we propose a numerical model for the coupling effect between wind flow and saltating sand particles to simulate wind-blown sand movement over the slope surface and use the SIMPLE algorithm to calculate wind flow and simulate sands transport by tracking sand particle trajectories. We furthermore compare the result of numerical simulation with wind tunnel experiments. These results prove that sand particles have obvious effect on wind flow, especially that over the leeward slope. This study is a preliminary study on windblown sand movement in a complex terrain, and is of significance in the control of dust storms and land desertification.

Morphology and formation mechanism of sand shadow dunes on the Qinghai-Tibet Plateau

The formation and development of dunes depend on wind-blown sand movement which is affected by the characteristics of sand material, topography, wind regimes and other factors. In this paper, we investigated two sand shadow dune groups in Shigatse and Za’gya Zangbo of Tibet and an individual dune in Da Qaidam of Qinghai, and analyzed their topographies and morphologies, and the physical characteristics of the sand, wind regime and sand transport. Formed under harsh conditions behind hills, these mature sand shadow dunes are hundreds of meters long, have significant ridges and crescent dunes downwind, and have a hill pass on one or both sides. Wind tunnel experiments revealed that the hill gap and wind velocity are important factors in the formation of these dunes. Sand shadow dunes formed only when the gap spacing is two-thirds of the hill height. When wind velocities are 20 m/s, the sand body is divided into two parts. The hill pass allows the transport of sand by wind, creating a “narrow-pipe effect”, which causes the transported material to gradually accumulate in the center of the shadow zone. We observed that the following are needed for sand shadow dunes to form: (1) strong winds, sufficient sand, suitable obstacles and a dry climate; (2) one or both sides of the obstacle forming the shadow zone must have a hill pass; and (3) the windward side of the obstacle must have a wide, flat area, providing adequate spacing for wind flow and transport of material and the leeward side must have a sufficiently broad, flat area to allow the release of the transported material. Research results on these newly discovered dunes on the Qinghai-Tibet Plateau could contribute to the understanding of dune geomorphology.

Numerical prediction on erosion damage caused by wind-blown sand movement

This study quantitatively investigated the erosion damage on the metal material caused by wind-blown sand under different environmental conditions (e.g. height and wind velocity) in aeolian processes. Wind-blown sand causes destructive impacts on buildings, abrasion of crops and many other damages in arid regions. Sand transport caused by wind often appears in the desert, open-pit mines and coastal dune fields, which is a special case of two-phase flow of gas and solids. Due to its special dynamic characteristics, the sand–wind system near the bed surface is complex and difficult to be solved by traditional computational fluid dynamics method. However, the steady-state saltation model is effective for describing the wind-blown sand movement. Therefore, this paper combines the solid particles erosion model with the steady-state saltation model to predict the erosion damages caused by blown sand. Correctness of the algorithm has been verified through the comparison of simulated results and experimental data of the sand flow structure. An early conclusion that the kinetic energy is crucial to erosion has been proved in this paper. The results show that the erosion rate varies with different variables, e.g. saltating velocity, saltating height, length, etc. The quantity of erosion shows stratification pattern as well as the mass flux of the sand flow. These results quantitatively show the major features of the erosion caused by wind-blown sand.

A numerical study of particle motion and two‐phase interaction in aeolian sand transport using a coupled large eddy simulation – discrete element method

AbstractWind‐blown sand movement, considered as a particle‐laden two‐phase flow, was simulated by a new numerical code developed in the present study. The discrete element method was employed to model the contact force between sand particles. Large eddy simulation was used to solve the turbulent atmospheric boundary layer. Motions of sand particles were traced in the Lagrangian frame. Within the near‐surface region of the atmospheric boundary layer, interparticle collisions will significantly alter the velocity of sand. The sand phase is quite dense in this region, and its feedback force on fluid motion cannot be ignored. By considering the interparticle collision and two‐phase interaction, four‐way coupling was achieved in the numerical code. Profiles of sand velocity from the simulations were in good agreement with experimental measurements. The mass flux shows an exponential decay and is comparable to reported experimental and field measurements. The turbulence intensities and shear stress of sand particles were estimated from particle root‐mean‐square velocities. Distributions of slip velocity and feedback force were analysed to reveal the interactions between sand particles and the continuous fluid phase.

Analysis of sand particles’ lift-off and incident velocities in wind-blown sand flux

In the research of windblown sand movement, the lift-off and incident velocities of saltating sand particles play a significant role in bridging the spatial and temporal scales from single sand particle’s motion to windblown sand flux. In this paper, we achieved wind tunnel measurements of the movement of sand particles near sand bed through improving the wind tunnel experimental scheme of particle image velocimetry (PIV) and data processing method. And then the influence of observation height on the probability distributions of lift-off and incident velocities of sand particles was analyzed. The results demonstrate that the observation height has no obvious influence on the distribution pattern of the lift-off and incident velocities of sand particles, i.e., the probability distribution of horizontal and vertical velocities of lift-off and incident sand particles follow a Gaussian distribution and a negative exponential distribution, respectively. However, it influences the center of the Gaussian distribution, the decay constant and the amplitude of the negative exponential distribution.

The characteristic of streamwise mass flux of windblown sand movement

Two patterns have been reported in previous literature about the streamwise mass flux of windblown sand movement in steady state; namely, the exponential pattern and the stratification pattern. Although the exponential pattern has been verified by some experimental measurements and numerical simulations, an agreed conclusion is not reached yet. Re-evaluating the previous model, it can be found that the pattern of the PDF (probability density function) distribution of the initial liftoff velocity is the key factor that determines whether the stratification happens or not. If the number of liftoff grains decreases with the increase in liftoff velocity, such as in the case of the exponential distribution, the stratification pattern will not appear. If the number of liftoff grains increases first and decreases later with the increase in liftoff velocity, such as in the case of the log-normal distribution, Gamma distribution and Gaussian distribution, the stratification pattern will come into existence. In addition, the hop height for the initial liftoff velocity, corresponding to the peak value of its PDF distribution, equals the height of the maximum streamwise mass flux. On the basis of some deterministic laws from experimental measurements and numerical simulations of grain/bed impact, a qualitative understanding about the PDF distribution of the liftoff velocity is obtained and the Rayleigh distribution is used for reptating grains. Also included in this paper is a model in which grain/bed impact is discussed and the interaction between the grains and the wind is considered. It is shown that the stratification pattern, composed of a linear increment layer, a saturation layer, and a monotonic decrement layer, indeed exists in the streamwise mass flux of windblown sand movement. Further, as with the average velocity and PDF distribution of the liftoff velocity of the reptating grains, which is determined by the characteristics of grains, the height of the peak value of the streamwise mass flux is also determined by the property of the grains and will be independent of the wind intensity.

Observation of Ground Temperature at Shallow Layer of Different Dune Types in the Tazhong Area

Land surface temperature affects the capability of long wave radiation,and it is an important parameter for studying climate change. The variation of air temperature and precipitation was often stressed in studying climate change in the Taklimakan Desert in the previous studies,but ground temperature in the desert was infrequently studied. In this paper,MicroLite 16K LITE5016 was used to examine the spatial distribution and temporal variation of ground temperature at shallow layer of different dune types in the Tazhong area located in the central Taklimakan Desert,where oceanic airstream is difficult to arrive. The Tazhong area is characterized by a typical continental climate with frequently and intensely wind-blown sand movement. The area of mobile dunes in Tazhong occupies more than 80% of the total area of the Taklimakan Desert. Temperature variation here is drastic,the maximum temperature is as high as 45.6 ℃,and the diurnal-nocturnal temperature difference is over 40 ℃. The annual sunshine duration in this area is 2 700 hours,accumulated temperature ≥0 ℃ is over 4 000 ℃,and the total solar radiation is 5 700-6 000 MJ/m2. Precipitation in this area is low,the annual precipitation is no more than 50 mm and only 4-5 mm in minimum,and it is extremely arid climate. The values of ground temperature at different depths (0 cm,10 cm and 20 cm) over a mobile dune and an artificially-fixed dune in the Tazhong area were measured during the period from August 3rd to 10th,2009. The results are as follows:(1) Daily range of ground surface temperature was high in summer both for mobile dune and artificially-fixed dune,it was decreased with the increase of depth,and it was the lowest at depth of 20 cm; furthermore,the maximum ground temperature occurred 2 hours later from noon,and the minimum one occurred at dawn; (2) The ground temperature of artificially-fixed dune was lower than that of mobile dune; (3) The difference between ground temperature and air temperature was the highest in summer; (4) Wind speed affected significantly the ground surface temperature regardless of mobile dune or artificially-fixed dune.

Visualization and laser measurements on the flow field and sand movement on sand dunes with porous fences

The installation of windbreak sand fences around sand dunes is one of the most promising methods to suppress windblown sand movement. In the study reported in this paper, we investigated the influence and validity of a small fence mounted on a model sand dune, in order to understand the fence’s suppression mechanism on the sand movement. The flow field around the dune and the process of sand-dune erosion were measured using LDV, PIV, and laser-sheet visualization techniques. A non-porous fence was found to suppress sand movements in its upstream area, but to enhance erosion downstream of the fence. This intensive erosion was caused by separated shear flow from the leading edge of the fence. In this study, four levels of porosity rate of the fence were tested. The fence-porosity dependences of the turbulent flow field and the erosion were discussed. The shapes of eroded sand dunes were found to depend on the porosity rate. The relationship between the sand-dune erosion and the flow field around the dune was illustrated with schematic diagrams. We concluded that the most desirable fence porosity should be 30% in order to avoid dune erosion if installed at a middle height on the stoss surface of a dune. This porosity provides a mean velocity reduction with avoiding a separated flow, although the flow bleeding through the porous fence is accompanied by grid turbulence and induces serious erosion in a narrow space behind the fence. Furthermore, we confirmed that the empirical correlation of the critical friction velocity can be applied to sand movements influenced by a fence.

SPH Method for Simulation of Wind-Blown Sand Movements

Wind-Blown sand movement is a complicated, non-linear, self-organized and two-phase flow. Conventional theory of mechanics and existing experimental observation method can’t describe that inherent mechanism exactly, and then appeared much difficulty of numerical method for computational simulation of wind-blown sand movement. In this paper, the smoothed particle hydrodynamics (SPH) method is used for simulating the wind-blown sand movement process. According to the characteristic of wind-blown sand movement the sand grains phase and the gas phase are modeled by considering the different kernel function and the particles size, mass, density, velocity and other physical quantities, which can movement along with controlling equation. Finally the numerical simulations are conducted for wind-blown sand movement and some reasonable results are obtained.