Particle Saltation Research Articles

Experimental Bench-Scale Study on Cuttings-Bed Erosion in Horizontal Wells

Abstract Cuttings-beds formation while drilling wellbores is a common challenge, especially for horizontal wells, as drilled particles have higher area to be deposited and form cuttings-beds, which can cause several problems such as increased torque and drag, pipe sticking or pipe breakage, among others. Removal of the drilled cuttings is done by circulating a suitable drilling fluid through the wellbore. This paper presents results from laboratory tests with deposited cuttings-bed and the flow of a fluid to erode the bed. The simulated cuttings-bed is a 1 m long deposited sand-bed in a horizontal section. Three different types of fluids are being used in the tests. To investigate how the rheological properties can affect the erodibility of the cuttings-bed, water (as a Newtonian fluid), a xanthan gum solution, and a water-based drilling fluid prepared for an offshore field operation (as a non-Newtonian fluids) are applied. Ultrasound measurements together with differential bed weight have been used to analyze the fluid–bed interaction. Results have shown that the cuttings-bed is eroded by dune movement. Saltation and dragging of sand particles due to the fluid flow appear to create a crest and then avalanche them down. The different types of fluids undergo different shear rates from the same pump power as the viscosity changes, as well as flow rates dependency along the dune extent.

Lifting and Transport of Martian Dust by the Ingenuity Helicopter Rotor Downwash as Observed by High-Speed Imaging From the Perseverance Rover.

Martian atmospheric dust is a major driver of weather, with feedback between atmospheric dust distribution, circulation changes from radiative heating and cooling driven by this dust, and winds that mobilize surface dust and distribute it in the atmosphere. Wind-driven mobilization of surface dust is a poorly understood process due to significant uncertainty about minimum wind stress and whether the saltation of sand particles is required. This study utilizes video of six Ingenuity helicopter flights to measure dust lifting during helicopter ascents, traverses, and descents. Dust mobilization persisted on takeoff until the helicopter exceeded 3m altitude, with dust advecting at 4-6m/s. During landing, dust mobilization initiated at 2.3-3.6m altitude. Extensive dust mobilization occurred during traverses at 5.1-5.7m altitude. Dust mobilization threshold friction velocity of rotor-induced winds during landing is modeled at 0.4-0.6m/s (factor of two uncertainty in this estimate), with higher winds required when the helicopter was over undisturbed terrain. Modeling dust mobilization from >5m cruising altitude indicates mobilization by 0.3m/s winds, suggesting nonsaltation mechanisms such as mobilization and destruction of dust aggregates. No dependence on background winds was seen for the initiation of dust lifting but one case of takeoff in 7m/s winds created a track of darkened terrain downwind of the helicopter, which may have been a saltation cluster. When the helicopter was cruising at 5-6m altitude, recirculation was seen in the dust clouds.

Particle saltation trajectories in supercritical open channel flows: Roughness effect

AbstractBed load sediment transport governed by particle saltation in supercritical open channel flows causes bedrock incision in high‐gradient mountain streams and hydro‐abrasion at hydraulic structures. Hence, a better understanding of turbulent flow characteristics and particle dynamics is of prime importance for the prediction of river and landscape evolution, and for a sustainable design of hydraulic structures. To this end, we experimentally investigated single‐particle dynamics in supercritical open channel flows over fixed planar and abraded beds covering smooth, transitionally rough, and hydraulically rough regimes. The experiments were performed at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of ETH Zürich in a wide range of hydraulic conditions with various channel width‐to‐depth aspect ratios (b/ho) and Froude numbers (F). We investigated the motions of five particle groups differing in shape, hardness, and diameter. By means of a high‐speed camera, the particle velocities and trajectory parameters—such as hop height and hop length—were determined using particle tracking velocimetry. The results reveal that at least 120 individual particles should be used in the tests to determine sound statistics of particle trajectories. In the present test conditions, the particles are dominantly transported in saltation. The effects of particle properties such as shape and diameter on the particle trajectories are negligible, while the rolling probability of the particles for a given flow condition increases with increasing diameter. Bed roughness was found to be the key parameter having a significant effect on the saltation trajectories and horizontal energy transfer. Hop height, hop length, and particle velocities, as well as horizontal energy transfer, increase with increasing bed roughness. Based on the saltation trajectory data, non‐dimensional equations are developed for each hydraulic regime and used to enhance the saltation–abrasion model of Sklar and Dietrich. The present findings contribute to a better understanding of particle motion characteristics under different hydraulic and roughness conditions, and their effect on the mechanics and prediction of bedrock incision and hydro‐abrasion in three‐dimensional supercritical open channel flows occurring in steeply sloped rivers and at hydraulic structures.

Numerical Analysis of Motion Characteristics of Sliding or Rolling and Saltation of Sediment Particles under Turbulent Flow

The processes of sediment particle movement were studied through numerical simulation using a coupled method with focus on discussing the characteristics of sliding or rolling and saltation sediment particles, respectively. Turbulent flow was simulated using large eddy simulation (LES). The sediment particle was simulated using the combined finite-discrete element method (FDEM). The interaction forces of turbulent flow and sediment particle were calculated using the immersed boundary method (IBM). It indicated that the collisions of saltating particle with low concentration increase the saltation length and flight time. In response, sediment particle velocity also increases. The particle angular velocity is largest at the takeoff moment, and decreases gradually in the saltation progress. The drag and lift forces near the bed are large, and away from the bed decrease and trend to be a stable value, gradually. From the relative magnitudes of the drag and lift forces, the lift force plays a more important role than the drag force in the sediment saltation. The relative magnitudes of drag and lift forces influence the incident and takeoff angles. The sediment transport rate calculated based on the characteristics of saltation sediment particles is overestimated, ignoring the effect of sliding or rolling sediment particles and inter-particle collisions.

Granule Ripples in the Kumtagh Desert, China: Morphological and Sedimentary Characteristics, and Development Processes

AbstractGranule ripples are widespread on Earth and are a fundamental component of dryland sedimentary systems, but the relationship between their wavelength and surface particle size is unclear; in addition, their sedimentary bedding and granule ripple development are incompletely understood. In this study, we examined the relationship between granule ripple development, morphology, and the surface grain‐size distribution. We measured the morphology and particle‐size distribution of granule ripples in China's Kumtagh Desert, and found an exponential relationship between ripple wavelength and average crest particle size, which contradicts previous results. We hypothesize the ripples resulted from creep of coarse particles caused by saltation impacts, accompanied by decreasing bed elevation, leading to crest migration and increased crest height. The size composition and wind regime determined the movement mode of particles, which controlled ripple development and size, but dry–wet and freeze–thaw cycles also contributed. We established a new conceptual model for the development of large granule ripples. Sand ripples and small granule ripples develop similarly, but large ripples did not form from merger of smaller ripples. We report for the first time that particles between 2.3 and 4.7 mm in diameter were missing in the ripple crests (confirmed in wind tunnel experiments). This gap affects the particle movement mode. Since the threshold wind speed for particle saltation at 4.7 mm approaches the regional maximum wind speed, quantifying the missing particles may permit prediction of regional maximum wind speeds, and has practical significance for identifying wind conditions elsewhere, including the surface of Mars.

Aeolian sediment transport on Io from lava\u2013frost interactions

Surface modification on Jupiter’s volcanically active moon, Io, has to date been attributed almost exclusively to lava emplacement and volcanic plume deposits. Here we demonstrate that wind-blown transport of sediment may also be altering the Ionian surface. Specifically, shallow subsurface interactions between lava and Io’s widespread sulfur dioxide (SO2) frost can produce localized sublimation vapor flows with sufficient gas densities to enable particle saltation. We calculate anticipated outgassing velocities from lava–SO2 frost interactions, and compare these to the saltation thresholds predicted when accounting for the tenuous nature of the sublimated vapor. We find that saltation may occur if frost temperatures surpass 155 K. Finally we make the first measurements of the dimensions of linear features in images from the Galileo probe, previously termed “ridges”, which demonstrate certain similarities to dunes on other planetary bodies. Io joins a growing list of bodies with tenuous and transient atmospheres where aeolian sediment transport may be an important control on the landscape.

Response of Flow and Saltating Particle Characteristics to Bed Roughness and Particle Spatial Density

AbstractWith the goal to explore the effects of natural bed roughness on bedload transport, numerical simulations of flow and particle saltation are carried out with varying bed roughness and particle spatial density. A combination of Eulerian and Lagrangian point‐particle methods is applied to solve the equations of motion of the fluid and the particles within the large‐eddy simulation framework. Flows over smooth and rough beds with four particle densities are considered. As the bed roughness increases, there is a leftward shift of the double‐averaged streamwise velocity profiles against dimensionless vertical distance, which is scaled with the bed roughness height, an upward shift of the peak values of double‐averaged Reynolds stresses, and a fragmentation and disappearance of coherent structures in the form of high‐speed and low‐speed near‐bed streaks. These observations are consistent with those of previous studies. As the bed roughness increases, the mean resting time of saltating particles increases, however the particles' saltation length, velocity, and angular velocity decrease, while their saltation height remains almost unchanged. Saltation height, saltation length, particle angular velocity, and resting time exhibit linear, gamma, normal, and exponential distributions, respectively. Further, as the bed roughness increases, the kurtosis and skewness of some particle parameters vary, and the particle velocity shifts from a symmetrical normal to an asymmetrical gamma distribution.

A mathematical conjecture associates Martian TARs with sand ripples

Abstract Considering that aeolian sand ripples are formed primarily by creeping particles caused by wind-driven saltation sand particles, we obtain a formulation for determining the height of saturated aeolian sand ripples by incorporating the reptation fluxes with previous experimental results on migration velocities of sand ripples. Based on existing observational results of terrestrial sand ripples on Earth's surface, it estimates that the wavelength of aeolian sand ripples on Mars is generally up to several meters. This implies a possibility that there is another sand ripple on Mars similar in scale to Transverse Aeolian Ridges (TARs) at some time when surface saltation was prevalent. Moreover, perhaps part of the widely observed TARs is the degradation of saltation sand ripples, whose formation is intimately related to saltation and reptation of sand particles. While the other two types of ripple-like morphologies (plain ripples and crater ripples) found by Opportunity Rover are essentially not. Further, we propose that the main factor controlling the scale feature of Martian sand ripples is the intense particle-bed collision process.

A numerical model for snow drifting simulations on flat roofs using Lagrangian approach

A numerical model based on Lagrangian description is developed in this study to predict wind-induced snow drifting on flat roofs, which fully considers the key physical processes of snow particle saltation. A scaled experiment of snow redistributions on the model roof was carried out in the wind tunnel for the verification and evaluation of different numerical methods selected from related literature. The optimal model is determined by comparing the predicted transport rate on the roof with estimations from empirical formulas and by comparing simulated snow distributions with experimental data. Characteristics of the saltation layer above the flat roof surface are then presented in detail based on the developed model. The rebound particles account for approximately 60% of the total transported particles above the roof, indicating the dominant role of rebound in the lift-off process for saltating snow particles. The developing snow transport along the roof span leads to the increase of surface erosion flux caused by the splash entrainment with downwind distance. The splash entrainment could thus contribute considerably to unsaturated snow transport on the flat roof, which is also found to be influenced by the approaching wind velocity and threshold friction velocity to varying degrees.

Prediction of particle saltation velocity for horizontal dilute phase negative pressure pneumatic conveying

The evaluation of particle saltation velocity is vital for the design of dilute negative phase pneumatic conveying systems. Nonetheless, the particle saltation velocity in dilute negative phase pneumatic conveying is largely understudied, it also lacks a consistent correlation over operating conditions and particle properties. As such, this paper investigates the effects of solid-gas ratio, particle size, and drill pipe rotational speed on particle saltation velocity in the drill pipe via CFD-DEM (computational fluid dynamics-discrete element method) simulation. Consequently, the particle saltation velocity increased gradually seemingly leaning toward a constant value with the increase of solid-gas ratio. The particle saltation velocity with larger particle size under similar solid-gas ratio was higher, while the speed of the drill pipe and the particle saltation velocity showed a negative correlation. The correlation for particle saltation velocity was established by dimension analysis method geared toward accurately predicting the particle saltation velocity in dilute negative phase pneumatic conveying. A comparison of the new correlation and the experimental data found that the error between the predicted value of the correlation and the measured particle saltation velocity is within 20% and the correlation derived by the dimensional analysis method give the well agreement.

Bacterial Characteristics of Dust Particle Saltation in Gobi Dust Sites, Mongolia

The Gobi Desert is a major source of Asian dust events, and the resulting health hazards have increased significantly in recent years. We reported that a variety of live bacteria were distributed in the Gobi Desert in relation to land use. Bacterial distribution was confirmed in the environment and on the land used by animals; however, bacterial saltation due to dust events has not been investigated in detail. In this study, to understand the distribution of surface bacteria in the atmosphere by dust saltation, live bacteria in four dust-generating areas in the Gobi area were monitored using an artificial dust generating device. The live bacteria were detected by experimental saltation at a wind speed of 6.5–8 m/s in all areas. A certain number of live bacteria are constantly saltated by dust events, and these bacteria depend on land use. Moreover, the bacterial saltation strain depended on land use and diversity, indicating that live bacteria are lifted into the environment by dust events. These findings indicate that dust events saltate environmental bacteria on the ground, suggest the risk of animal-derived bacterial saltation affected by land use, and present cross-border public health challenges to be considered in the future.

Large Eddy Simulation of Particle Transport and Deposition Over Multiple 2D Square Obstacles in a Turbulent Boundary Layer

AbstractPredicting solid particle transport in the lowest parts of the atmosphere is a major issue for man‐made obstacles in semi‐arid regions. Here, we investigate the effects on solid particle saltation, of square obstacles on the ground with different spacings. The aerodynamic field is determined by large eddy simulations coupled with an immersed boundary method for the obstacles. Solid particles are tracked by a Lagrangian approach. Take‐off and rebound models are introduced for the interaction of particles with the wall. Without particles, fluid velocity profiles are first compared with experiments (Simoens et al., 2007, https://doi.org/10.1016/j.atmosenv.2007.08.013) showing good agreement. Special focus is put on the recirculation zone that plays an important role in solid particle entrapment.Particle concentration fields are presented. Accumulation zones are studied regarding the different obstacle spacings as an extension of the aerodynamic scheme by Oke (1988, https://doi.org/10.1016/0378-7788(88)90026-6) to solid particle transport. A deposition peak appears before the first obstacle. When the spacing between the two obstacles is large enough, some particles are trapped within the recirculation and a second deposition peak arises. The streamwise evolution of the horizontal saltation flux shows that the lowest flux downstream of the obstacles is obtained for the highest separation. The deposition rate or the streamwise saltation flux are estimated globally as a function of obstacle spacing. These results illustrate how the numerical tool developed here can be used for assessing air quality in terms of solid particle concentration.

Sensitivity analysis of fine dust spreading from litter in poultry houses

Poultry houses are one of the major sources of agricultural particulate matter (PM) emissions into the environment. Litter properties, poultry activities, and indoor climate of poultry houses are the main parameters that influence the dust emission, but precise quantitative effects and their interactions are hardly known. The objective of this study was to gain quantitative insight into the dust spreading process from poultry litter by using the discrete parcel method (DPM) and global sensitivity analysis (GSA).The dust spreading process includes the creep, suspension, and saltation of fine particles was simulated with the DPM within the aerial region close to the litter. The simulations proved that a collision between an object and the litter should happen to release particles from the litter into the air. It was indicated that the released particles with a diameter ≥30 μm and particle density ≥1400 kg m −3 were deposited on the litter for all tested air velocities. Also, particles <10 μm diameter remained suspended for airflow velocities >1.5 m s −1 . The GSA indicated that the creep process has a direct relation with the airflow velocity and coefficient of restitution and an inverse relation with the particle density and the coefficient of friction. Overall, it was shown that the DPM is a suitable numerical technique to simulate the dust spreading process, and hence, it can be recommended for future studies to examine this process on larger scales. • The DPM is a suitable numerical technique to simulate the dust spreading process. • A collision with sufficient energy should happen to release dust from litter into the indoor air. • The fine dust release process is very sensitive to the litter density and the airflow velocity. • The fine dust with a diameter smaller than 10 μm will not settle in the presence of airflow. • The creep process is less sensitive to the coefficient of restitution between litter particles.

Thermal-hydraulic and fouling performances of enhanced double H-type finned tubes for residual heat recovery

• Both thermal-hydraulic and anti-fouling performance of double H-type finned tubes are investigated. • Grooves can create secondary saltation of fly ash particles and reduce the fouling. • LVGs can result in more particles colliding with fin surface and increase the fouling. • An advanced fin structure with three pairs of grooves and one pair of LVGs is recommended. Heat exchangers for residual heat recovery in coal-fired power plants face the issues of low heat transfer efficiency of flue gas side and the fly ash fouling. However, heat transfer enhancement structures always increase the fouling on the fin. Efficient methods are required to improve both heat transfer and anti-fouling performance of the heat exchanger. In present study, the thermal-hydraulic and anti-fouling performances of enhanced double H-type finned tubes are numerically investigated using the discrete phase model coupled with particle deposition and removal model. Five types of double H-type finned tubes with different layouts of grooves and longitudinal vortex generators (LVGs) are investigated to improve both thermal-hydraulic and anti-fouling performance of fin. The effects of particle diameter, flue gas velocity and layout of enhanced structures are discussed. It is found that the transverse vortex induced by grooves can lead to the secondary saltation of fly ash particles, which will significantly reduce particle deposition on fins. However, the longitudinal vortex generated by LVGs can result in the fly ash particles with saltation mode or suspension mode colliding with fin surface, which causes more particle deposition on fins. The recommended fin with three pairs of grooves and one pair of LVGs can enhance heat transfer by 12.92–16.63% with 21.75–30.72% flow resistance penalty and reduce the fouling rate by 2.4–23.7% for particle diameter under 20 μm. It can be considered as a promising heat transfer component for heat recovery in coal-fired power plants.

EFFECT OF PIPE INCLINATION ON COARSE-GRAINED PARTICLE-WATER MIXTURES FLOW

The effect of the mixture velocity, solid concentration, and pipe inclination on the coarse-grained particle–water mixtures flow behaviour, concentration distribution, and pressure drops were experimentally studied in horizontal, vertical, and inclined pipes of inner diameter D=100 mm. Graded basalt gravel was used as a solid phase. The local concentration distribution was studied with the application of a gamma-ray densitometer. The study revealed the stratified flow pattern of the coarse particle-water mixture in horizontal and inclined pipes. The particles moved principally close to the pipe invert, and particle saltation becomes the dominant mode of particle conveying for higher and moderate flow velocities. The frictional pressure droops in ascending pipe increases with increasing pipe inclination up to about 30 degrees, then gradually decreases. For the pipe inclination lower than about 30°, the effect of pipe inclination on local concentration distribution was not significant. The in-situ concentration reached higher values in the ascending than in the descending sections.

Spatiotemporal sediment transport and deposition processes in experimental dilute pyroclastic density currents

Dilute pyroclastic density currents (dilute PDCs) are frequent and highly dangerous flows of hot gas and particles occurring at explosive volcanoes. The study and interpretation of the sedimentary characteristics of their associated deposits is one of the most important approaches to better understand these violent phenomena and to characterise their dynamics, frequency and magnitude in the geological record of volcanoes. Current strategies are based on sediment transport principles developed for fluvial and aeolian systems. How well these analogies capture the sediment transport behaviour of dilute PDCs remains poorly understood, as the hot and hostile conditions of these fast-moving volcanic flows hamper direct measurements.Here we report the results of large-scale experiments that aim to synthesise the behaviour of dilute PDCs in order to investigate the transport and sedimentation processes inside the hot flows. These flows reproduce the spatiotemporal deposit facies variations seen in natural deposits of dilute PDCs. Through measurements of the evolving flow structure (velocity, particle concentration and flow grain size distribution), we show that the lower region of the density stratified current can be subdivided from the aggrading deposit upwards into a dynamic bedload region with particle concentrations of c. 0.5 to several vol%, a transient region with particle concentrations of c. 0.1–1.5 vol%, a dilute, fully turbulent region with formation of mesoscale clusters, and an upper dilute turbulent region absent of mesoscale clusters. We show that the particle feeding mechanisms of the transient region is related to the occurrence of mesoscale clusters. This process has a key role in modifying the sediment transport modes inside the bedload region. These modifications cause a variation of the dynamics of the lower flow boundary, including erosion/deposition events, and variations of the deposition rate over at least three orders of magnitude. We present images and video footage of these processes that include the formation of shifting sandwaves, rolling and saltation of particles inside the experimental dilute PDC, and analyse how these relate to the development of massive, stratified and laminated deposit structures. Through mapping the isochrones of deposition across the flow length and measuring the propagating flow above, we capture a spatiotemporal view of the aggrading deposit, which can guide the interpretation of natural deposits.

Mechanics of bed particle saltation in turbulent wall-shear flow

In this paper, we explore the mechanics of bed particle saltation in turbulent wall-shear flow, analysing the forces on a particle to perform saltation. The hydrodynamic drag encompasses the form drag and turbulent drag. The hydrodynamic lift comprises the Saffman lift, Magnus lift and turbulent lift. The subtle role of the Basset force in governing the particle trajectory is accounted for in the analysis. The bedload flux, emanating from the mathematical analysis of bed particle saltation, is determined. The results reveal that for the particle parameter range 20–100, the transport stage function equalling unity corroborates the threshold of bed particle saltation, where the saltation height and length are 1.3 and 9 times the particle size. For a given transport stage function, the relative saltation height and length decrease with an increase in particle parameter. For the particle parameter range 20–100, the relative saltation height and length increase with an increase in transport stage function, reaching their peaks, and then, they decrease. For a given particle parameter, the peak and mean particle densimetric Froude numbers increase as the transport stage function increases. The bedload flux curves for particle parameters 26 and 63 produce the upper and lower bound curves, respectively.

Sand-turbulence interaction in a high-Reynolds-number turbulent boundary layer under net sedimentation conditions

Simultaneous two-phase particle image/tracking velocimetry (PIV/PTV) measurements are conducted on a particle-laden turbulent boundary layer (TBL) over a horizontal smooth-flat plate under net sedimentation conditions. Dilute desert sand grains with a median diameter of 203 μm and bulk volume fraction of O(10−5) are used as the discrete phase, and the characteristic Reynolds number of the TBL is relatively high (Reτ = 5500 based on the friction velocity uτ and boundary layer thickness δ). The two-dimensional velocity filed in the streamwise/wall-normal plane is measured by four CCD cameras aligned along the streamwise direction, which resolves a wide spectrum of the scales, ranging from small-scale energetic eddies to large-scale motions (LSMs) in the TBL. An improved phase separation algorithm and discrete particle matching method are developed for two-phase measurements. The results presented here provide new information concerning the effect of high-inertia particles with a dilute concentration on wall-bounded turbulence, especially at high Re. Analysis of the velocity spectrum of the gas phase reveals, for the first time, that the presence of sand grains with a size on the order of the Kolmogorov length scale attenuates turbulence fluctuation by suppressing small-scale sweep-ejection cycles in the near-wall region. A critical layer (y/δ = 0.12 or y+ = 670) is found to partition the streamwise evolution of both the local concentration and the streamwise mean velocity of the sand grains into a non-equilibrium near-wall region and a quasi-parallel outer region. In addition, a balance between the strength and probability between the sweep and ejection events of sand grains is reached at this layer. Such a critical layer might be a good indicator of the upper bound of the particle saltation process, in which LSMs are believed to play a significant role.

Bed particle saltation in turbulent wall-shear flow: areview.

Bed particle saltation in turbulent wall-shear flow remains an intriguing phenomenon in applied hydro-dynamics. In this review, we report the current state of the art of bed particle saltation in turbulent wall-shear flow, highlighting the physical characteristics of bed particle saltation and its mathematical modelling. A critical appraisal of the mechanics of bed particle saltation is presented thorough ample experimental evidence. The salient features of bed particle saltation, encompassing the saltation height, saltation length, particle velocity, saltation duration, particle collision with the bed, particle rotation, particle resting time and particle re-entrainment, are thoroughly discussed. Both the deterministic and computational fluid dynamics approaches in modelling bed particle saltation are summarized, and the subtle role of the hydrodynamic forces is elaborated. The estimation of bedload flux in a fluvial environment, emanating from the mathematical modelling of bed particle saltation, is delineated using different modelling approaches. Finally, the challenges in modelling bed particle saltation are highlighted, and a new look at bed particle saltation is furnished.

Reevaluation of the aeolian sand flux from the Ulan Buh Desert into the upper Yellow River based on in situ monitoring

Aeolian sand transport into rivers is a crucial factor influencing channel sediment dynamics and fluvial processes in rivers that flow through desert areas. Few studies have examined the dynamic processes, controlling factors, and the amount of aeolian sand transported into river channels. Here, we report a case study of aeolian sand transport into in the upper reaches of the Yellow River as it flows along the eastern margin of the Ulan Buh Desert, which is a major desert in northern China. The present study is based on systematic monitoring of wind flow characteristics, aeolian sediment dynamics (saltation, creep and suspension), and the migration of typical sand dunes (mobile, semi-anchored, and anchored) from 2013 to 2016. The relationship between wind speed and wind-blown sand transport in the study area was determined. The relationship between the rate of aeolian sand transport (saltation and creep) and the wind speed 2 m above the ground surface can be depicted with a polynomial relation when the wind speed is ≥5.7 m/s, and with a power function when the wind speed is <5.7 m/s. Dune migration mainly occurred during March to May, and the dune migration rate was influenced by wind speed and other factors such as dune height and vegetation conditions. The rate of aeolian sand transport by wind-blown sand flow (particle saltation, creep, and suspension) and sand dune migration were calculated, and the annual aeolian sand transport rates into the river channel in 2013, 2014, 2015 and 2016 were estimated to be 1.47, 0.86, 0.52, and 0.50 million t/yr, respectively. These results are significantly lower than previous estimates made between the 1980s and 2000s. The decrease in sand flux may be attributed to the regional decline in wind speed over the last six decades which has caused a sharp reduction of the aeolian sand transport rate, the improved vegetation coverage in this area which has reduced the area of active and mobile dunes, and an embankment constructed adjacent to the Yellow River which has suppressed aeolian sand migration into the river channel.