Search Results (11)

When high-speed trains (HSTs) rapidly enter or exit the wind barrier area of the bridge, the quick change in the operating environment can lead to sudden changes in train aerodynamic loads, resulting in the deterioration of their aerodynamic performance and adversely affecting safe and stable operation. In this paper, the effects of wind barrier porosity, crosswind speed, and train speed on the sudden change in the aerodynamic load of the HST induced by wind barriers are analyzed, and the reasons for the sudden change from a flow field perspective are given. Additionally, the influences of the buffer structure with three lengths of 45 m, 90 m, and 135 m on the sudden change in the aerodynamic load of HSTs are studied. The results show that the lower the porosity of the wind barrier, the higher the crosswind speed, and the lower the speed of trains entering and exiting the wind barrier area, resulting in a greater degree of sudden change in the aerodynamic load of the HST. The buffer structure measuring 90 m in length is considered the most suitable, as it can significantly alleviate the sudden change in the aerodynamic load and effectively enhance the safety of train operations. Full article

Using porous wind barriers for the microclimate modification of agricultural lands, urban areas, and surrounding roads is a ubiquitous practice. This study establishes a new method for numerically modeling the turbulent flow in and around forest shelterbelts using an advanced multiple-relaxation-time lattice Boltzmann model (MRTLBM). A detailed description is presented for a large eddy simulation (LES) of turbulent winds by implementing barrier element drag force in the MRTLBM framework. The model results for a forest shelterbelt are compared with a field observational dataset. The study indicated that our implementation of drag force in MRTLBM is an accurate method for modeling turbulent flows in and around forest patches. Sensitivity analyses of turbulent flow related to the shelterbelt structure parameters and wind directions are also carried out. The analysis indicated that the optimal wind shelter effect in reducing the mean wind speed and turbulent kinetic energy is maximized using a narrow, medium porosity shelterbelt, with the wind direction perpendicular to the shelterbelt. These conclusions are in agreement with other observational and modeling studies. Finally, the computational time of a central processing unit (CPU) and graphics processing unit (GPU) was compared for a large domain with 25 million grids to demonstrate the MRTLBM advantage of LES in regards to computational speed with a mixed forest and building environment. The GPU is approximately 300 times faster than a CPU, and real-time simulation for this large domain is achieved using the Nvidia V100 GPU. Full article

Urban vegetation plays a crucial role in reducing atmospheric particulate matter (PM), modifying microclimates, and improving air quality. This study investigates the impact of a laurel hedge (Laurus nobilis L.) on airborne PM, specifically total suspended particulate (TSP) and respirable particles (PM₄) generated by a Diesel tractor engine. Conducted in a wind tunnel of approximately 20 m, the research provides insights into dust deposition under near-real-world conditions, marking, to our knowledge, the first exploration in a wind tunnel of this scale. Potted laurel plants, standing around 2.5 m tall, were arranged to create barriers of three different densities, and air dust concentrations were detected at 1, 4, 9, and 14 m from the plants. The study aimed both to develop an experimental system and to assess the laurel hedge’s ability to reduce atmospheric PM. Results show an overall reduction in air PM concentrations (up to 39%) due to the presence of the hedge. The highest value of dust reduction on respirable particles was caused by the thickest hedge (three rows of plants). However, the data exhibit varying correlations with hedge density. This study provides empirical findings regarding the interaction between dust and vegetation, offering insights for designing effective hedge combinations in terms of size and porosity to mitigate airborne particulate matter. Full article

This paper introduces a kind of double-row reed–nylon net combined sand barrier. Using the computational fluid dynamics (CFD) method and the Euler–Euler double-fluid model, the new sand fences’ windproof effect and airflow features are simulated under different porosities and spacings, and the optimal configuration parameters are selected. The new sand fence has better windproof performance and practical significance than double-row reed and double-row nylon net fences. The new sand fences with a porosity of 0.3–0.4 and spacing of 28 H provide a longer protection range and a better wind protection effect. Considering the serious sand damage in China’s Taklamakan Desert, the new fences’ impact on sand buildup is examined. The combined sand fences have powerful sand blocking and accumulation effects, even though there is only a small quantity of sand accumulation on the leeward side of the second row. The sand particles primarily settle between sand fences in the center and rear areas. The combination of sand fences made of different materials combines the advantages of both, improves the construction efficiency and service life, and provides a more economical and efficient sand barrier arrangement for the arrangement of wind and sand-blocking facilities around railroads and highways in desert areas. Full article

Sand barriers are one of the essential measures used to prevent wind and sand disasters on expressways in desert areas. The article uses Fluent numerical simulation to consider different heights, as well as different spacing from two perspectives, and determine the ideal vertical height of sand barriers (porosity is fixed at 20%). Adding to existing wind and sand flow field research, our analysis of the wind speed and sand characteristics reveals the changing rules that affect a single group of high vertical sand barriers along the highway when considering different parameters and measuring the wind and sand performance. At the same time, we also use field research to verify the accuracy of numerical simulation. The study shows the following. (1) When the airflow passes through the single group of vertical sand barriers, it will form a deceleration zone, acceleration zone, turbulence zone and stabilization zone in different areas, and the overall distribution of the wind and sand flow field is in the shape of a “W”. (2) When the spacing is 4 H, the maximal wind speed in the transition area of the sand barriers is two to three times bigger than that when the spacing is 2 H, which is not conducive to the accumulation of sand particles. When the spacing is 1 H, the maximum wind speed of the two rows of sand barriers is two to three times bigger than that when the spacing is 2, and the two rows of sand barriers overlap in wind protection performance, reducing the overall protective capacity of the sand barriers. (3) As the height of the sand barriers continues to grow, the protective performance of the sand barriers is also enhanced. In the same position around the sand barriers, the wind speed under the 2.5 m sand barriers is lower than that under the 1.0 m sand barriers by 2–3 m/s. It is suggested that the height of the sand barriers should be controlled at 1.5–2.0 m in the actual deployment, and 2 H spacing should be used. Full article

Wind-blown sand significantly affects the construction and safe operation of railways in desert regions. The performance of a wind-blown-sand prevention system with different structural parameters and sand accumulation around the railway subgrade was analyzed in this study. The optimum porosity and opening type of a second sand fence were assessed via wind tunnel experiments and numerical simulations. The results showed that the subgrade intercepted some sand and reduced sand accumulation on the track surface, and the interception rate was 29.70%. The wind-blown-sand prevention efficiency of the subgrade was 88.55%. Moreover, the lower the porosity of the second sand fence, the lower the sand velocity on the windward side and the higher the sand accumulation. The porosities of the first and second sand fences should be 30% and 20%, respectively, to maximize the sand accumulation between the fences. When the second sand fence had horizontal openings, most of the sand accumulated near the surface (within 20 cm) on the leeward side and on the straw checkerboard barrier, and the maximum wind-blown-sand prevention efficiency was 97.16%. When the second sand fence had vertical openings, the efficiency was 93.60%, and the sand accumulation on the leeward side and the straw checkerboard barrier was reduced. As the fence height increased (above 20 cm), the sand prevention efficiency of both approaches increased. The research results can provide guidance for the formulation and optimization of sand prevention measures for railways and highways in deserts. Full article

Wind barriers play a vital role in protecting saplings until maturity when planted as vegetative windbreak forests. Most previous studies have focused on the porosity of wind barriers, but no studies have simultaneously examined the effects of the porosity and inclination, despite the potential of the inclination to decrease wind speed. We tested three wind barrier cases in wind tunnel experiments: (1) Case A (porosity of 0% with inclinations (90°, 80°, and 70°)), (2) Case B (porosity of 25% with inclinations (90°, 80°, and 70°)), and (3) Case C (porosity of 50% with inclinations (90°, 80°, and 70°)). The vertical and horizontal wind velocities were measured at three vertical and seven horizontal points behind the barriers. The results demonstrated a statistically significant decrease in the correlation between the distance and mean wind velocity for all cases, with up to a six-fold wind protection effect. The wind barrier with 0% porosity and a 90° inclination provided the highest degree of wind protection. However, the wind protection range was limited downwind, and recirculation of wind flow could occur in the leeward direction, potentially damaging saplings. A wind barrier with 50% porosity and 70° inclination sufficiently decreased the wind velocity and prevented recirculation of wind flow, demonstrating that both porosity and inclination considerably impacted the wind protection effect by reducing wind velocity. Our findings offer novel insights into the influence of wind barriers with varying porosities and inclinations and can provide valuable guidance for constructing efficient windbreak forests. Full article

Understanding the crosswind stability of cars under strong wind loads and research on wind resistance methods is important for improving the safety performance of wind-induced driving on bridges. Taking van-body trucks as the research object, numerical calculation methods and wind tunnel test methods are used to conduct the wind-induced driving safety analyses of van trucks on a cross-sea bridge. The influence of the structural parameters of the barrier-type wind barrier on the aerodynamic characteristics and straight-line driving stability of the trucks on the bridge is studied and analyzed quantitatively. The results show that the decrease in the porosity of the wind barrier can effectively reduce the average wind speed of the bridge deck, and increasing the height of the wind barrier can effectively reduce the wind speed and increase the occlusion height of the bridge deck. The lateral acceleration, yaw rate, and lateral displacement of trucks decrease with the decrease in the porosity of the wind barrier and decrease with the increase in the height of the wind barrier. The research conclusions can not only provide data support for wind-induced driving safety analysis and the wind-resistant design of bridges but also provide a new method to balance the requirements of bridge wind-induced driving safety and bridge wind-induced structure safety. Full article

Wind barriers can effectively reduce the risk of overturning and derailment of high-speed trains running on a bridge under crosswind. However, it can adversely affect the wind resistance of the bridge. There are few studies on the aerodynamic performance of curved wind barriers. In this paper, the effects of curved wind barriers with four curvatures (0, 0.2, 0.35, and 0.50) and different train-bridge combinations on the crosswind aerodynamic characteristics of a train-bridge system are investigated. The results show that the curved wind barrier can significantly reduce the wind speed below a certain height on the bridge deck. The curved wind barrier with small curvature can better reduce the aerodynamic force of the train; however, it greatly increases the aerodynamic force of the bridge. A wind barrier with a curvature of 0.35 is recommended because it takes into account the aerodynamic characteristics of the train and bridge at the same time. The porosity of a wind barrier greatly influences the aerodynamic performance of the train on the track of the windward side of the bridge, while the wind barrier has little effects on the train on the track of the leeward side of the bridge. The aerodynamic performance of the train on the track of the windward side of the bridge is less affected by whether or not a train on the track of the leeward side of the bridge is present. Full article

This paper focuses on field measurements and analyses of train-generated wind loads on wind barriers (3.0 m height and porosity 0%) with respect to different running speeds of the CRH380A EMU vehicle. Multi-resolution analysis was conducted to identify the pressure distribution in different frequency bands. Results showed that the wind pressure on the wind barrier caused by train-induced wind had two significant impacts with opposite directions, which were the “head wave” and “tail wave”. The peak wind pressure on the wind barrier was approximately proportional to the square of the speed of the train, and the peak wind pressure decreased rapidly along the wind barrier height from the bottom of the wind barrier. The maximum wind pressure occurred at the rail surface height. Furthermore, results of the multi-resolution analysis illustrated that the energy of the frequency band from 0 to 2.44 Hz accounted for 94% of the total energy. This indicated that the low-frequency range component of the wind pressure dominated the design of the wind barrier. The frequency of pulse excitation of train-induced wind loads may overlap with the natural frequency of barriers, and may lead to fatigue failure due to cyclic loads generated by the repeated passage of high-speed trains. In addition, the speed of the train had a negligible effect on the energy distribution of the wind pressure in the frequency domain, while the extreme pressure increased slightly with the increase of the speed of the train. Full article

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. Full article