When the wind speed or fluid shear in the bed exceeds the critical value for particle entrainment, the sediment particles on the erodible bed surface will be blown into the airflow, and the wind will cause soil erosion, leading to some environmental problems in arid and semi-arid areas. Drylands such as sandstorm disasters, atmospheric dust particle pollution and land degradation (Sterk et al., 1996, Leenders et al., 2007, Dong et al., 2010) have additional impacts on agricultural production and human health. Therefore, controlling soil wind erosion becomes an important research topic. For example, a common method is to design and optimize windbreak walls with different structures (e.g. fences or porous screens, protective belts and forest belts). by the shielding effect ( Woodruff and Zingg, 1953, Heisler and Dewalle, 1988, Cornelis and Gabriels, 2005, Torita and Satou, 2007, Li and Sherman, 2015, Cheng et al., 2020). In addition to reducing wind speed, vegetation also suppresses soil loss by covering part of the soil surface and trapping sediment particles entrained in the airflow (Wolfe and Nickling, 1993). In arid and semi-arid areas, although plant interactions can be largely neglected, sparse vegetation also leads to an apparent reduction in soil wind erosion (Buckley, 1987). Erosion and sand deposits often occur around these windbreaks or the only obstacle (Iversen et al., 1990, Iversen et al., 1991, Cornelis and Gabriels, 2005, McKenna Neuman et al., 2013). In order to assess the sand control effect of these obstacles, it is important to study erosion and sand deposition around a single obstacle. By providing a quantitative prediction method for sand erosion/deposition due to complex wind flows around obstacles, more effective countermeasures can be developed (Tominaga et al., 2018).
The topography of the bed surface around obstacles changes due to the loss and deposition of particles through sediment transport (e.g. Iversen et al., 1990, Iversen et al., 1991, McKenna Neuman et al., 2013, Tominaga et al. , 2018) and the resulting complex erosion and deposition pattern around a single obstacle is related to the shape of the obstacle and the air density (Iversen et al., 1990, Iversen et al., 1991). Erosion typically occurs on the lateral and upwind side of a surface-mounted cylindrical roughness element (Iversen et al., 1990, Iversen et al., 1991, McKenna Neuman et al., 2013), but for a very short period of time (aspect ratio smaller). as 0.1, defined as the ratio of the height h to the diameter d of the cylinder), deposition occurs on the windward side and there is also greater erosion in the far wake (Iversen et al., 1990, Iversen et al., 1991) . Tominaga et al. (2018) measured the change in the erodible bed surface area around a cube (0.2 m on a side) over time and found that the erosion zone is near the leeward corners of the cube, which is similar to the rectangular prism experimental results. (height = 8 cm, width = 16 cm, downwind dimension = 8 cm) (Iversen et al., 1990, Iversen et al., 1991), but the area of erosion on the sides of the rectangular prism was much larger. The topography around the cylinder is obviously different from that of the cube and the block. There is an area of severe erosion on the leeward side of the cylinder, but no obvious upwind erosion for the cube and block. The experiment by McKenna Neuman et al. (2013) also showed that different types of erosion occur on a flat surface around the cylinder, hemisphere, edge cube, and face cube.
As the airflow passes through the surface mounted asperities, various coherent vortex structures are created, such as: a horseshoe vortex, a drag vortex, a Kármán road vortex, and a bow vortex (Kawamura et al., 1984, Sau et al., 2003, Sumner et al., 2004, Pattenden et al., 2005, Uffinger et al., 2013 , Sumner, 2013), thereby changing the wind speed around the roughness element and the shear stress of the fluid acting on the bed surface, affecting sand transport in the bed. Therefore, the role of flow structure or vortex structure in adjusting microtopography has received much attention (Sutton and McKenna Neuman, 2008).
In the erodible bed, when the ejected particles enter the airflow, the flow becomes more complicated by one roughness element, as the moving particles and the evolution of the microtopography affect the local surface shear stress as well as the flow pattern beyond the obstacle (Iversen et al., 1991). On the other hand, the roughness element affects the trajectories of moving particles colliding with the windward side of the roughness element, and protects the bed surface from the wind of the roughness element from impact and particle ejection. Therefore, the surface shear stress distribution around the roughness element is less uniform. Although the upwind surface shear stress is below the threshold, erosion can occur around rough elements since the maximum shear stress values around the cylinder can be above the threshold (Iversen et al., 1990).
To better understand the erosion properties around a surface-mounted roughness feature, it is necessary to study the process of topography evolution and its relationship to airflow. There are many experimental studies of the air flow field around a single roughness element on a solid flat surface. However, studies on the airflow field in the case of topography evolution are lacking, mainly due to the difficulty of measuring the airflow field in the case of topography evolution. The numerical simulation method CFD (Computational Fluid Dynamics) has been employed as a powerful tool for solving fluid problems and is used to simulate the airflow field around an obstacle or the airflow field under moving boundary conditions (e.g. relief deformation or boundary deformation). For example, Tominaga et al. (2018) introduced the topography evolution equation caused by the sand transport rate to simulate the microtopography evolution around a single cube and the corresponding airflow field, but did not consider the influence of particles on the sand transport rate. air flow and there is still a big difference in quantity. Farimani et al. (2011) simulated the transient flow in a deformed sand pile using a moving boundary method. Although the topography change around a cylinder and a block over time has been reported in some studies, it is difficult to obtain complete information about the surface height distribution, so it is still necessary to measure the microtopography around a single block. Roughness element at different times to provide effective distribution. Data to verify the numerical model.
Because the shape and structure of the plant is very complex, this article simplifies the plant in a cylinder to study the process of topography evolution around an isolated cylinder and its effects on airflow. Existing results of the microtopographical features of a fixed roughness element have improved our understanding, but the cylinder aspect ratio is typically less than 3.0, and studies of the microtopography around a cylinder with a larger aspect ratio are lacking. Therefore, two types of cylinders are used in this work, the diameters of which are 2 cm and 1 cm, respectively, and the aspect ratios are 2 and 8, respectively. The variation in bed microtopography around the isolated cylinder over time is measured in a wind tunnel. Based on the measured results of bed topography evolution, the airflow field is then simulated using the moving boundary method. Finally, the micro-topographical features around an isolated cylinder, the corresponding air flow velocity and the surface shear stress are analyzed.
The scheme and the picture of the experimental setup are shown in Fig. 1. Two types of cylinders are used: one is 4.0 cm high and 2.0 cm in diameter, designated C1, and the other is 8.0 cm high and 1.0 cm in diameter, designated C2 . They have the same frontal area and the aspect ratios (=h/d, i.e. the ratio of the height h to the diameter d of the cylinder) are 2.0 and 8.0, respectively. The experiments were conducted in the wind tunnel of the State Key Laboratory of Earth Surface Processes and Resource
Experimental results of the development of the topography of the bed around the cylinder
The evolution of the microtopography of the bed around the cylinder can be expressed by the spatial and temporal variation of the height of the bed surface. Fig. 6 and Fig. 7 show the spatial distribution of the bed surface height at different times for the two cylinders, where the airflow is along the positive x-axis direction and the cylinder is at coordinate (0, 0), represented by a black one Point. Youf0is the free current wind speed. HBis the height of the surface of the sand bed, which was previously zero
The end faces of the two cylinder types (one is h=4.0 cm and d=2.0 cm, the other is h=8.0 cm and d=1.0 cm) are the same and their aspect ratios are 2 and 8, respectively. From the previous analysis, it appears that they have a different impact on the microtopography of the soil. Compared to the taller and thinner C2 cylinder (aspect ratio 8), there is a larger erosion area around the shorter and wider C1 cylinder (aspect ratio 2) and also a V-shaped deposit ridge. Larger according to Lee (Fig. 6, Fig. 8
The basic features of the bed microtopography around the present cylinders (aspect ratios 2 and 8) are that a deep pit or scour surrounds the cylinder and a straight ridge connects a symmetrical V-shaped ridge. It appears downwind, the size of which is affected by the aspect ratio. Both erosion (hB<−2mm) and deposit (hB>2mm) the areas of the shorter and wider cylinder (aspect ratio of 2) are larger than those of the taller and thinner cylinder (aspect ratio of).
Contribution statement by CRediT
Liqiang Kang:Methodology, Research, Writing - Original Draft, Writing - Proofreading and Editing, Visualization, Formal Analysis.Wen Zhang:Investigation.Xueyong-zou:Formal Analysis.
Declaration of competitive interest
The authors declare that they have no competing financial interests or known personal relationships that may have influenced the work described in this article.
This work is supported by the National Natural Science Foundation of China (No. 41871003).
Experimental study of erosion-deposition properties around isolated plants of different shapes in a wind tunnel
2022, WindforschungSee AlsoSoil shrinkage data analysisPhymatolithon - an overview | ScienceDirect TopicsMikrotopografia on mustan tuhkan kosteikkojen kasvillisuuden ja maaperän kemian perustavanlaatuinen organisaatiorakenne.Surface Roughness vs. Surface Finish | AR and RMS | Astro package
The flexible plant 2 bends under the action of the wind, resulting in a better shielding effect on the leeward sand bed surface, so the area of sand deposition behind plant 2 is much larger than that behind plant 3. The above analysis shows that the microtopography pattern (spatial distribution of erosion and deposition) is related to the shape of the plant, mainly because roughness elements alter the local airflow structure (McKenna Neuman and Bédard, 2015; McKenna Neuman et al., 2021; Kang et al., 2021). ). For example, airflow around the cylinder over the dense bed results in more flow stagnation on the windward side and greater turbulent momentum dissipation near the two sidewalls compared to the flatbed, while lift in the leeward area causes some vortex structures to disappear (McKenna Neuman and Bedard, 2015).
An accurate description of the erosion and depositional characteristics around unique model plants of different shapes is important to assess the protective function of plants in wind erosion control. The temporal variation in bed topography was measured in a wind tunnel for two flexible models and two rigid tree models. The height of the bed surface near the plant decreases and a deep pit forms, while on the leeward side there is generally a depositional area, the shape of which depends on the plant species. The local wind erosion rate on both sides generally decreases over time, and the Lee depositional area with less than zero local erosion rate gradually moves downwind over time while disappearing for the formed plant model. Tree with a long trunk and a large crown. Among similar frontal areas of plants, both the areas of erosion and deposition around the short-stemmed, conical-crown tree plant and the flexible, large-top, small-bottom plant are generally larger than those visible. They are thin and thin flexible around the plant. Attachment. The rigid tree-like plant with a short trunk and a dense conical crown is better suited for erosion control due to the lower net erosion rate and area of erosion similar to the depositional area, while the other plant models have a higher net erosion rate and a much larger area of erosion. erosion area.
Influence of the number of entry boundaries and locations on gas diffusion and flow in a typical chemical industrial park near rough terrain
2022, process safety and environmental protection
After hitting the obstacles, the wind first flows along the walls of the obstacles and then changes direction when it reaches the edge. Therefore, there is a low wind speed zone (u/Uref<0.5) downwind of the obstacles, and this phenomenon is consistent with other studies (Kang et al., 2021; Ma et al., 2017). . Downwind of the storage tanks is a low velocity zone due to the wind shear created after hitting the tanks.
Accurately simulating the spread of contamination over rough terrain with intricate obstacles is a difficult but important scientific and technological problem. The input limit was important, and weather factors with only one limit (e.g., wind speed and direction) were commonly used for computational fluid dynamics (CFD) simulation. However, on rough terrain with complicated obstacles, boundary weather conditions can be very different. Entering a single limit can lead to large simulation uncertainty. Accordingly, the influence of different input boundary numbers and locations on the CFD simulation was investigated using a field experiment with low trace gas content, which was carried out in a chemical industrial park in a mountainous area. The experimental results suggested that the diffusion of the gas was influenced by a combination of meteorological conditions from the boundaries of several inputs. The simulation results confirmed and showed that the commonly used single-point limit entry can lead to large inaccuracies. The case where the entry limits are close to the emission sources and intersect with the crosswind plane agrees better with the measurements. The number of entry boundaries and locations has also been found to have a significant impact on velocity and turbulence. Finally, a guideline for setting entry limits was proposed. This study can improve understanding of CFD simulation and is useful for selecting input weather locations for accurate forecasts.
investigative articleSee AlsoTree dieback, woody plant diversity, and topography-related ecosystem in semi-arid montane forests: Implications for ecosystem managementInfluence of size on the dielectric properties of fine-grain BaTiO3 ceramicsLyhyen kantaman digitaalinen fotogrammetrinen havainnointijärjestelmä maaperän pinnan morfologian mittaamiseen jatkuvan sateen aikanaSuunniteltu 2D/2D/2D Bi2WO6/Ti3C2/SnNb2O6 Z-kaavion heteroliitos kemiallisen rajapinnan sidoksen kautta ja parannettu fotokatalyyttinen aktiivisuus
Changes in physicochemical properties of old stabilized sand dunes due to atmospheric sediments and clay mineral diversity in an arid zone
Aeolian Research, Volume 50, 2021, Item 100674
Sand dune hills stabilized by oil mulch and biological methods in south-west Iran. The aim of the present study is to determine the impact of these landscapes on airborne dust retention in five regions including hillside (UH), hillside (DH) and treetop positions at 54 years. These locations were at different distances from dust sources and prevailing winds. The results showed that the salinity in the study areas showed the following trend: canopy > UH > DH. Four times more mud particles were trapped in the corner than in the interior areas. In addition, the sludge deposition flux was 54 g−2Year−1(the minimum) at the inner site (Al-Baji) at 207.4 g−2Year−1(the maximum) at the corner location (SG). Unlike Schlick, clay flow was greatest at high altitudes in both the interior (124.4) and corners (123.4) due to the movement of fine materials. Total material deposition (silt+clay) was maximum (330.8 g) and minimum (155.6 g).−2Year−1) in the corner and interior areas. The mineralogy of the clays indicated that these mounds contained two mineral groups. The primary minerals, i.e. carbonates and silicates, were inherited from the starting materials. Secondary minerals were identified in surface soil and subsurface peaks were very faint. Windblown sediments contributed these clays to the surfaces. The abundance of these clays showed the following trend: paligorskite > smectite > vermiculite. It was found that these areas do not disturb the atmosphere with dust and play an important role in air purification, since the roughness of the surface of these mounds has been promoted by artificially planted trees.
Assessing the role of lichens in preventing dust emissions in arid regions: a case study in northeastern Iran
Aeolian Research, Volume 50, 2021, Item 100697
The dominance of wind processes in dry areas has created a harsh environment for soil and vegetation in these regions, where soil fertility, ecosystem productivity, air clarity and human health depend on wind activity and dust emission rate. Biological soil crusts (biocrusts) are communities of living organisms on the soil surface that play an important role in soil ecosystem services in arid regions. Lichens are organisms that can accumulate certain elements or substances in high concentrations in the atmosphere. The relationship between lichen species and soil geochemistry and dust uptake in the geomorphic zones of north-eastern Iran was investigated. Different lichen species and soil particles were analyzed using scanning electron microscopy (SEM-EDS). The results of the XRF and XRD analyzes showed that the lichen crusts affected the mineralization of the soil. By creating a microtopography, he indicated that the lichen trapped the dust. They also increased the amount of clay on the soil surface. The results showed the important role of lichens in soil ecosystem services in arid regions.
A Laser Sheet Sensor (LASS) to measure the flux of windblown sand
Aeolian Research, Volume 50, 2021, Item 100681
There is a trend to use high frequency piezoelectric, acoustic and optical sensors to measure wind sand transport rates in the wind community. However, most of these sensors are particle counters with inconsistent sensitivities or low saturation limits. Here we present a commercial Laser Sheet Sensor (LASS) that can be used streamwise to measure local salt flow or perpendicularly to capture the voluminous character of sand flows. The results of our laboratory and field experiments show that LASS sensors respond linearly to sand flows in the range from 0 to 20 kgm.−2S−1, covering most of the wild jumping events. LASS are extremely consistent. They maintain functionality even with minor lens contamination or laser misalignment during use. LASS should not be used in environments with wet or poorly sorted sand or uneven winds.
investigative articleSee AlsoVaihtoehtojen kehittäminen mukautuvalle metsätaloudelle: Pinus-lajin puiden kasvun harvennus- ja kuivuuskestävyys korkealla rinteellä Etelä-EspanjassaMetsärakenne ja puulajien monimuotoisuus maailmanlaajuisesti merkittävän biologisen monimuotoisuuden Abasumba-alueella, GhanaParkinsonin tauti: biokemiallinen reitti, joka sopii kaikkiin geeneihin?
Trace evidence and rare earth elements from windsand source areas in the Mu Us Desert of northwest China
Aeolian Research, Volume 50, 2021, Item 100683
Tracing the origin of wind sands in the Mu Us Desert is crucial for understanding surface processes in arid and semi-arid regions of China. However, the material source of the wind sands in the Mu Us desert is still up for debate. The origin of modern wind sands in different areas and with different particle sizes in the Mu Us Desert remains unclear, as does the relationship between the sources of different sediment types. Here, using a hierarchical cluster analysis, the Mu Us desert is divided into two sub-zones to the east and west. Based on the properties of trace elements and rare earths, we investigated the origin of eolian sands in different areas and with different particle sizes and analyzed the origin relationships between eolian sands, sandstones, fluvio-lacustrine sediments, loess sediments and floodplain sediments. in the desert. We report the following results: (1) The sources of coarse-grained eolian sands in the east and west of the Mu Us desert are different. The Aeolian sands in the eastern part are mainly derived from local sandstones and coarse-grained fluvio-lacustrine sediments from the east, while those in the western part are mainly from the Qilian orogenous belt on the northeastern Tibetan Plateau. (2) Fine-grained eolian sands throughout the desert show apparent homogeneity and have geochemical properties similar to fine-grained fluviolacustrine, loess and floodplain sediments, suggesting that these fine-grained fractions are fully mixed after a long time. long-distance transport. (3) Transport and deposition of wind sands are influenced by wind processes and river activity.
The distribution and nature of star dunes: a global analysis
Aeolian Research, Volume 50, 2021, Item 100685
Star dunes, found on Mars and Titan and also found in the Earth's stratigraphic record, are widespread in the world's arid regions and 25 provinces have been identified and characterized from an analysis of Google images. Earth. They are found in East Asia, West Asia, America, southern Africa and North Africa. Star dunes are absent from the inland sand seas of Australia, the Kalahari and Indian Oceans, and southern Sahara. Morphometric measurements at a variety of sites show a density of stellar dunes ranging from 7 to 81 per 100 km.2(average 30 per km2), dune widths from 125 to 3071 m (mean 895 m) and heights from 4 to 291 m (mean 75 m). Star dunes exhibit a wide variety of shapes, including simple pyramids, complex structures, checkerboard patterns, symmetric and asymmetric shapes, stars along linear dunes, and stars along transverse dunes. In some areas, star dunes are associated with megadomes. In this work they are grouped into 10 types, although it is clear that some dunes may have characteristics of more than one type. Star dunes form in areas of low rainfall, changing wind directions, and in conjunction with topographical barriers. They are a more widespread and diverse phenomenon than previously thought.
Effects of crops on soil texture during oasis expansion in Xinjiang, Northwest China: Effects of wind erosion
Aeolian Research, Volume 50, 2021, Item 100646
To study the effects of cultivation on soil texture at local and regional scales during oasis expansion, a field study combined with remote sensing monitoring was conducted in the arid desert regions of Xinjiang, northwest China. We assess possible changes by comparing cultivated and uncultivated land in 2019 with matching reference land from China's second national soil survey. The results showed that the clay and silt content in the cultivated land increased with the years of cultivation (p<0.05), while the sand content decreased. A comparison of clay and silt content between 2019 and the late 1970s showed the accumulation of fine particles in the center of the oases and the removal of fine particles at their edges. Our results also show that sand content increased in reclaimed land, vacant land bordering oases, and sandy land. A comparison of 15 paired reference samples revealed that in most plots the clay and silt content on arable land is higher than on adjacent uncultivated land, although some plots showed a decreasing trend, suggesting that the dose of agricultural cultivation is not always at one Increase in fine particles leads. We conclude that the initial difference in soil texture before reclamation and reclamation history result in differences in soil texture between cultivated and adjacent uncultivated land. During oasis expansion, reclamation of sandy soil can reduce wind erosion, suggesting that appropriate agricultural conservation and reclamation measures can mitigate the adverse effects of soil texture changes.
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