Wind Tunnel Simulation Experiments Research Articles

Effect of bridge height on airflow and aeolian sand flux near surface along the Qinghai-Tibet Railway, China

In this work, we studied the near-surface flow field structure of railway bridges with different heights through field investigation and wind tunnel simulation experiments. Meanwhile, we simulated the distribution of sand accumulation around a bridge via CFD software based on the sand accumulation around the Basuoqu bridge in the Cuona Lake section of the Qinghai–Tibet Railway. Results show that the sand around this railway bridge is mainly from the lake sediment on the west side of the railway and the weathered detritus on the east side. The height of the railway bridge in the sandy area affects the distribution of the near-surface flow field and the variation in speed on both sides of the bridge. The wind speed trough on both sides of the 6 m high bridge is higher, and the horizontal distance between the wind speed trough and the bridge section is 1.5 times that of the 3 m high bridge. Wind speed attenuates in a certain range on the windward and leeward sides of the bridge, forming an aeolian area; under the beam body, it is affected by the narrow tube effect, forming a wind erosion area. The height of the bridge determines its sand transport capacity. Under certain wind conditions, the overhead area at the bottom of the 3 m high bridge and its two sides do not have the sand transport capacity, so sand accumulates easily. Nevertheless, the sand accumulation phenomenon gradually disappears with the increase in bridge clearance height. The objectives of this study are to reveal the formation mechanism of sand damage for railway bridges, provide theoretical support for the scientific design of railway bridges in sandy areas, and formulate reasonable railway sand prevention measures to ensure the safety of railway running, which have certain theoretical significance and practical value.

Effects of blown sand and soil properties on the abrasion rate of compacted soil

Abrasion caused by blown sand is an important process for compacted soils in grasslands. The abrasion rate is affected by a combination of the blown sand intensity and the properties of the underlying soil, but there is a paucity of relevant studies of the simultaneous effects of these factors, especially quantitative ones. Our wind tunnel simulation experiments showed that the abrasion rate of compacted soil increased rapidly with increasing transport rate of the abrasive particles and with increasing soil texture index (δ = (sand% + silt%)/[clay% + organic matter% + CaCO3%]), and decreased significantly with increasing soil compaction. Accordingly, we developed an abrasion rate prediction model that accounted for the transport rate of windblown particles (abraders) and the physicochemical properties of the compacted soil. The effects of abrader properties (grain size and basic density), abrader availability, and a limited upwind supply of the abraders on the abrasion rate of compacted soils were also addressed. We developed a comprehensive abrasion-rate equation that accounted for both particle size and the basic density of the abraders.

The effect of double-row wing bag sand barrier on wind prevention and sand fixation: wind tunnel simulation and field verification

Introduction: Most of the sand fixation technologies utilized locally and internationally are static or dynamic, making it challenging for a single sand fixation mode to function in a harsh environment. Therefore, the development of a sand fixation mode that combines resistance and consolidation has emerged as a trending topic in sand control research. Our team developed the wing bag sand barrier, which is a static and dynamic combination of sand fixation mode.Methods: In this study, we examined the characteristics of airflow velocity field and sand resistance near double-row wing bag sand barrier under different wind conditions to screen out the optimal mode of wing bag sand barrier. The analyses were conducted under nine configuration modes through the wind tunnel simulation experiment and the field experiment.Results: The inflection point of the airflow was always 5H on the windward side of the wing bag sand barrier, regardless of the wind speed. The protection range of the wing bag sand barrier with the same specifications was gradually weakened with the increase of the wind speed. However, there was an upward trend in both total sand accumulation and sand accumulation of each height layer. When the wind speed was slower than 8 m/s, the sand accumulation behind the barrier was mainly concentrated in the 0–10 cm height layer, and when the wind speed was 12 m/s, it was mainly concentrated in the 30–60 cm height layer. At the leeward side of the wing bag sand barrier, sand particles were rejected in the range of 0–30 cm; however, they were conducted in the range of 30–60 cm. The protective effect of the wing bag sand barrier simulated in the wind tunnel experiment was consistent with that of the field experiment.Discussion: For a wind speed of slower than 6 m/s, the recommended specification for the field-installed wing bag sand barrier was 25 cm × 20 cm or 30 cm × 20 cm. The specifications 25 cm × 20 cm and 25 cm × 25 cm were recommended at an inlet wind speed of 8 m/s. When the wind speed was greater than 12 m/s, the recommended specifications were 25 cm × 25 cm, 25 cm × 20 cm, and 20 cm × 25 cm.

Wind Dynamic Characteristics and Wind Tunnel Simulation of Subgrade Sand Hazard in the Shannan Wide Valley of the Sichuan-Tibet Railway.

The Shannan wide valley section of the Sichuan–Tibet Railway is located in the middle reaches of the Yarlung Zangbo River, where sand hazard is severe. A wind tunnel simulation experiment was conducted by establishing a subgrade model and performing field observation to carry out research on the dynamic environment of blown sand and the sand hazard formation mechanism of subgrade in the Shannan wide valley. Observation results showed that the sand-moving wind of the Shannan wide valley was chiefly derived from the ENE direction, and the resultant sand transport direction was WSW. Wind speed, the frequency of sand-moving wind, the sand drift potential, and the maximum possible sand transport quantity were relatively high in the spring. Meanwhile, the dynamic of the wind-blown sand flow was further enhanced in the spring, particularly influenced by the flow action of the Yarlung Zangbo River. Thus, sand hazard mainly occurred in the spring. The Sichuan–Tibet Railway subgrade evidently changed the wind speed, the wind-blown sand flow field, and conditions of transport and accumulation. Within the distance of 5 times the model height in the windward direction and at the subgrade top center to 20 times the model height of the leeward direction was the wind speed deceleration zone, resulting in sand particle sediments. A wind speed acceleration zone appeared on the subgrade windward slope shoulder, resulting in wind-blown sand flow erosion. This study provides a scientific basis for sand hazard prevention and control in the Sichuan–Tibet Railway.

Experimental study on aerosol dry deposition characteristics in wind tunnel simulation

The radioactive aerosols are produced during the operation of nuclear power plants will cause certain harm to human body. Dry deposition is one of the important factors affecting the aerosols deposition to the ground, and radioactive aerosols and common aerosols have similar properties in terms of dry deposition. Based on the similarity theory, with the help of the newly built environmental wind tunnel of the China Institute for Radiation Protection, with a part of a nuclear power plant site as a research object, and the wind tunnel simulation experiment of aerosol dry deposition characteristics was carried out in groups. The particle dynamic analyzer (PDA) was used to measure and calculate the dry deposition velocity of aerosol particles, and the results are grouped, analyzed and discussed. The research results show that when the variables are controlled, when the underlying surfaces are the same, compared with aerosol particles with particle sizes of 0-2 μm and 2-5 μm, the dry deposition velocity of aerosol particles greater than 5 μm is more likely to change with the increase of wind speed.

The mechanism of sand damage at the Fushaliang section of the Liuyuan–Golmud expressway

Abstract The Liuyuan–Golmud Expressway is located in the extreme arid area inland of the Hexi Corridor and Qaidam Basin. This expressway, particularly its Fushaliang section, is prone to serious blown sand hazards. The causes of these hazards remain unknown, thereby hindering targeted sand prevention and control. The aim of this paper is investigate the mechanism of sand damage in Fushaliang by performing a field observation of the locale and conducting wind tunnel simulation experiments. Results show that the sand-moving wind in Fushaliang dominates in the northwest west (WNW) direction. The wind speed, sand-moving wind frequency, sand drift potential, and maximum possible sand transport quantity in Fushaliang are high during summer and low during winter, and the yearly resultant sand transport dominates in the southeast east (ESE) direction. The wind route in Fushaliang is approximately perpendicular to the dominant wind and sand transport directions. During summer, sand materials are blown by the wind from WNW to ESE, after which they are blocked by the expressway roadbed. An area with high wind speed is observed at the shoulder of the windward roadbed slope that leads to a blown sand flow erosion. Meanwhile, low wind speed areas are observed –5H at the upwind direction of the roadbed and from the shoulder of the leeward slope of the roadbed to the 15H downwind direction. These areas accumulate sand materials at the up- and down-wind directions and then release them to the leeward slope of the roadbed, thereby resulting in blown sand hazards. The findings of this work can guide the prevention and control of sand damage in this section of the expressway.

Wind Dynamic Environment and Wind Tunnel Simulation Experiment of Bridge Sand Damage in Xierong Section of Lhasa–Linzhi Railway

The Lhasa–Linzhi Railway is located in the sandy area of the South Tibet valley, with high elevation and cold temperature. The Xierong section is a bridge section where blown sand hazards are severe. However, the disaster-causing mechanism of blown sand hazards in this section is currently unclear, thereby hindering targeted sand prevention and control. To address this problem, the wind dynamic environment of and causes of sand damage in this section are investigated through the field observation of the locale and a wind tunnel simulation experiment. Results show that the dominant sand-moving wind direction in the Xierong section is SSE. The wind speed, frequency of sand-moving wind, sand drift potential (DP), and maximum possible sand transport quantity (Q) in this section are relatively high during spring (March to May) and low during other seasons. The yearly resultant sand transport direction (RDD, RA) is SW. The angle between the route trend of this section and the sand transportation direction is 30°–45°, and the sand source is located in the east side of the railway. During spring, sand materials are blown up by the wind, forming blown sand flow and movement from the NE to SW direction. Increased wind speed area is formed between the top of the slope shoulder of the windward side of the bridge and the downwind direction of 3H, causing blown sand erosion. Meanwhile, weakened wind speed areas are formed within the distance of -3H at the upwind direction and from the downwind direction of the 3H to 20H of the bridge. These areas accumulate sand materials at the upwind and downwind directions of the bridge, thereby resulting in blown sand hazards. This research provides a scientific basis for the prevention and control of sand damage in the locale.

A Wind Tunnel Study of the Seasonal Shelter Efficiency of Deciduous Windbreaks

HighlightsSeasonal leaf shedding is a key factor affecting the airflow field and shelter efficiency of deciduous windbreaks.The wind deceleration region around modeled Elaeagnus angustifolia L. (Russian olive) windbreaks was larger in winter than in summer, but the intensity of the wind speed reduction was relatively low.The shelter efficiency of E. angustifolia windbreaks in winter was not less than 80% of that in summer.Abstract. The shelter efficiency of windbreaks constructed with deciduous plants changes with their phenological stage. We used Elaeagnus angustifolia L. (Russian olive) as an example and investigated the airflow field and shelter efficiency of deciduous windbreaks with summer facies (with leaves) and winter facies (without leaves) by means of scaled wind tunnel simulation experiments. Our study revealed that different canopy seasonal porosities exert different wind speed reductions inside the windbreaks, which also determine the upwind and downwind wind speed variation. The variation in wind speed was greater in summer than in winter. For the windbreak with summer facies, a large wind acceleration region above and before the windbreak and a strong wind deceleration region inside and after the windbreak were observed. The wind deceleration region around the windbreak with winter facies was larger than that in summer, but the intensity of the wind speed reduction was relatively low. The results of our study further show that although E. angustifolia windbreaks are highly porous in winter, the shelter efficiency was not less than 80% of that in summer. Like any wind tunnel study on windbreaks, producing an artificial plant model that is highly similar to the real field plant is difficult. Nevertheless, our results clearly revealed the wind reduction patterns of deciduous windbreaks due to seasonal porosity caused by leaf shedding, which may provide valuable data for assessing the shelter efficiency of deciduous windbreaks. Keywords: Airflow field, Elaeagnus angustifolia, Seasonal porosity, Wind reduction.

Application of Boundary Layer Displacement Thickness in Wind Erosion Protection Evaluation: Case Study of a Salix psammophila Sand Barrier.

Since the establishment of blown sand physics, surface roughness has been widely used in current research to indicate the ability of a surface to resist wind erosion and to evaluate the windproof effect of protective measures. However, since the calculation of surface roughness can result in different values and its applicability is poor, there are disadvantages to its use. Therefore, it is proposed that the boundary layer displacement thickness should be used rather than roughness as an indicator to solve such problems. To analyze the new indicator’s accuracy and applicability when evaluating the effect of protective measures, a wind tunnel simulation experiment on a typical mechanical protection measure commonly used for sand control in China was conducted. Indicators of roughness and boundary layer displacement thickness were compared in evaluating the windproof performance of a Salix psammophila sand barrier of differing heights, side lengths, and porosities. The wind speed acceleration rate and effective protection area, which can directly reflect the protective effect of a sand barrier, were analyzed as evaluation criteria. The results show that roughness can only reflect the influence of height on the windbreak effect of sand barriers, whereas the boundary layer displacement thickness accurately showed the influence of height, side length, and porosity on the windproof effect of the sand barriers. Compared with roughness, the boundary layer displacement thickness was more strongly correlated with the effective protection area. Therefore, the boundary layer displacement thickness, rather than roughness, should be used as a new indicator when evaluating the windproof effect of protective measures.

A Simple Parametrization for the Concentration Variance Dissipation in a Lagrangian Single-Particle Model

A model for the evaluation of the concentration fluctuation variance is coupled with a one-particle Lagrangian stochastic model and results compared to a wind-tunnel simulation experiment. In this model the concentration variance evolves along the particle trajectories according to the same Langevin equation used for the simulation of the velocity field, and its dissipation is taken into account through a decay term with a finite time scale. Indeed, while the mean concentration is conserved, the concentration variance is not and our model takes into account its dissipation. A simple parametrization for the dissipation time scale is proposed and it is found that it depends linearly on time and on the ratio between the size and the height of the source through a scaling factor of 1 / 3.

Cogitation on developing a dynamic model of soil wind erosion

Studies on soil wind erosion began with single factors affecting soil wind erosion; with increasing quantities of data being accumulated, the wind erosion equation (WEQ), the revised wind erosion equation (RWEQ), the wind erosion prediction system (WEPS), and other soil wind erosion models have been successively established, and great advances have been achieved. Here we briefly review the soil wind erosion research course and analyze the advantages and disadvantages of the current soil wind erosion models. From the perspective of the dynamics of wind erosion, we classified the factors affecting soil wind erosion into three categories, namely, wind erosivity factors (WEF), soil antierodibility factors (SAF), and roughness interference factors (RIF). We proposed the concept of a standard plot of soil wind erosion to solve the problem of uncertainty of the soil wind erosion modulus on a spatial scale, and provided methods to set similarity conditions in wind tunnel simulation experiments and to convert the spatial scale of the wind erosion modulus from the standard plot to a large scale field. We also proposed a conceptual model on the basis of the dynamics of soil wind erosion with the theoretical basis that wind produces a shear force on the soil surface. This shear force is partitioned by barely erodible soil surfaces and roughness elements on the ground, and the amount of soil loss by wind should be calculated by comparing the shear force of the wind on barely erodible soil surfaces with the anti-erosion force of the surface soil. One advantage of this conceptual model is that the calculated soil wind erosion modulus is not subject to changes of spatial scale. Finally, we recommended continual improvement of the existing models while also establishing new models.

Effect of non-tillage with straw mulch on wind erosion in irrigated oases of Hexi Corridor

通过风洞模拟试验，对不同留茬高度（20 cm和40 cm）和不同留茬方式（立秆留茬和留茬收后压倒）下的土壤风蚀量和不同处理在25～250 mm内的风速廓线进行定量测定，并分析土壤风蚀速率与风速的关系。结果表明，高留茬免耕处理在吹蚀风速20 m·s^-1以下时对土壤的防风蚀作用存在显著影响。立秆留茬40 cm的风蚀速率比传统耕作降低87.84%，比相同留茬量的压倒留茬处理降低5.89%，表现为最小风蚀速率，且对吹蚀风速的减弱作用最强，防风蚀效果最好。进一步研究表明，传统耕作的土壤风蚀速率（Q）与风速(V)呈幂函数关系,而免耕处理的土壤风蚀速率（Q）与风速(V)遵循二次函数关系。

Effects of the homogeneous traffic on vertical dispersion parameter in the near field of roadways – A wind tunnel study

The vertical dispersion parameter of Pasquill–Gifford needs some modification in the close vicinity of urban roadways by considering the influence of traffic-induced turbulence. Wind tunnel simulation experiments have been carried out with controlled traffic parameters to evaluate traffic-induced effect on vertical dispersion parameter (σz) in the near field of roadways. The aerodynamic similarities in atmospheric flow, vehicles size and speeds have been considered with appropriate similarity criteria. The tracer gas experiments have been performed to evaluate σz in the near field of the roadways for variable traffic volumes and two approaching wind directions (i.e. 90○ and 60○). The results showed that the value of σz increased monotonically with increase in traffic volumes and becomes nearly constant at a particular downwind distance. It has also been found that the σz was considerably affected by approaching wind directions. Further, the comparison of experimental σz values for both approaching wind directions with those of Chock (1978) and Rao and Keenan (1980), showed an agreement within ±15%.

Wind tunnel simulation experiment and investigation on the electrification of sandstorms

Electric discharge phenomenon is often observed during the passage of sandstorms over desert regions and sometimes does great damage to human beings. Based on previous researches on the electrification of sandstorms by the scholars both at home and aboard, the authors conducted the simulation experiments on the electric fields of sandstorm-triggered creeping-saltating sand, suspending sand and watered suspending sand in the large-scale wind tunnel. According to the experimental results the electric field structure and its formation mecha-nism were analysed and discussed, the quantity of electric charges and electric field strength were measured and calculated, and finally several conclusions were drawn.

Wind tunnel simulation of wind loading on low-rise structures: a review

A review of existing and new considerations for the assessment of wind loads on low-rise structures from wind tunnel simulation experiments is presented. Attention is given to the aerodynamics of surface-mounted prisms, followed by a discussion of the atmospheric flow characteristics near the surface under a variety of atmospheric and upwind terrain conditions. In the final section, detailed recommendations and requirements are presented for the appropriate conduct of these experiments. The content of this article provides detailed justification for wind tunnel simulations based primarily on the duplication of the turbulence intensities and small-scale turbulence of the incident flow. In order to satisfy the latter requirement, it is recommended to utilize models of low-rise buildings that have a scale not smaller than 1:50. Less emphasis should be placed on duplication of the integral scale of the turbulence, as duplication of both scales requires equality of the Reynolds number that cannot be achieved in wind tunnels. Duplication of either the Jensen number ( H/ z o) or the power-law exponent of the mean velocity profile is insufficient to guarantee the proper duplication of the necessary turbulence parameters. For homogeneous upwind terrain and near-neutral stability, the pertinent turbulence parameters can be obtained from basic principles without the use of empiricism. For terrain with scattered upwind obstacles (Δ x>15), the turbulence parameters can be obtained above the blending height with the use of the “regional” roughness length. For a closer spacing of the roughness obstacles (Δ x<15), the displacement height should be included in the analysis to obtain values of the turbulence parameters. For all situations, the simulation of the turbulence in the atmospheric surface layer should be based on duplication of the pertinent flow parameters above the blending height. Comparison of either flow or pressure measurements requires that both the sampling rate and record length be properly matched in model and full scale. Comparison of peak pressure coefficients is only meaningful if they have the same level of probability.

Roughness estimation for wind-load simulation experiments

Wind Engineers engaged in wind tunnel simulation experiments for the assessment of wind loads on low-rise structures have to cope with the problem of how to reproduce the pertinent flow parameters characterizing the atmospheric surface layer. Seldom are field observations available, and for the majority of the cases the simulation is therefore not based directly on observed flow quantities at the building site. Instead the Wind Engineer must assess visually the roughness of the terrain at the building site and match it with a particular class from an existing terrain classification. The latter provides then a measure of the roughness in the form of the roughness length that can be used to provide an estimate of the turbulence parameters of the flow to be reproduced in the laboratory using basic principles. The proposed method to obtain these parameters can be easily adapted for a user-friendly electronic evaluation with the prescribed roughness length.

Influence of pebble mulch on soil erosion by wind and trapping capacity for windblown sediment

In the semiarid region of northwest China, pebble mulches have been used by farmers for over 300 years. However, very little studies were conducted on the effect of pebble mulch on soil erosion by wind. Results of a wind tunnel simulation and a field experiment showed that pebble mulch had two functions in controlling wind erosion: first, it could prevent soil from eroding by wind; second, it could trap dust carried by wind. According to the wind tunnel simulation experiment, pebble mulch reduced wind erosion rate (g m −2 min −1) by 84–96% at the different wind velocities (10–26 m s −1) in comparison with the controls. In addition, the ratio between total soil loss from the pebble-mulched soil and the bare soil was 0.06. The field study indicated that pebble mulch could trap 1.6–1.8 times more windblown sediments than the control suggesting that pebble mulch might also be effective in controlling dust storms. The grain size distribution of eroded soil showed that a lower percentage of particles in the range of >1.0 mm fractions and a higher percentage in the range of <0.05 mm fractions occurred in the pebble-mulched treatments than in the controls, while windblown sediments trapped by pebble mulches had a lower percentage of grains in the range of >0.5 and <0.05 mm fractions than that trapped by the controls.

Wind tunnel simulation experiment of mountain dunes

Mountain dunes can be categorized as echo dunes, climbing dunes and falling dunes. Their formation, development and movement are relative to sand source, flowfield near the ground, angle of mountain slope and ground subsisted environment. Through field observation and wind tunnel simulation, this paper discusses the physical mechanisms at each stage of development of mountain dunes, and reveals the principal and subordinate actions between main and lateral flow, and important actions of retarded and accelerated flow, secondary flow and separated flow. The main conclusions are: pressure coefficient on the stoss slope increases with the increase in wind velocity u∞, angle of attack β and angle of slopeα , while on the lee slope its variation is just the opposite; and the maximum slope for the formation of climbing dunes or the minimum slope for the formation of echo dunes are varied and decrease with increasing β .

Wind tunnel simulation of the surface layer flow for the prediction of wind loads on low-rise structures

The flow in the atmospheric surface layer over non-uniform terrain is analyzed with emphasis on those properties which are essential for the prediction of wind loads from wind tunnel simulation experiments. Near the surface, horizontal turbulence components are not in equilibrium with either the velocity profile or with the local terrain. Use of the “local” roughness length as a representative scaling length for wind tunnel model studies (Jensen's law) may simulate the velocity profile but is inadequate for simulation of the turbulence intensities of the horizontal velocity components. The discrepancies between profile and turbulence become larger as the regional terrain increases in complexity.