Search Results (9)

The inhibitory effect of vegetation on soil wind erosion along grassland highways in semi-arid regions has not been fully elucidated. In this study, the dry vegetation near S105 provincial highway in the Sangendalai area of Xilingol League, Inner Mongolia was selected for a wind tunnel test, and the vegetation coverage and porosity during the test were determined by using image processing methods. On this basis, a porous medium model of dry vegetation was established, and the two-phase flow of wind and sand was numerically simulated. The results show that: (1) The numerical simulation results are in good agreement with the wind tunnel observations, confirming the feasibility of using CFD to simulate wind erosion affected by vegetation along grassland highways in semi-arid areas. (2) The aerodynamic roughness of the grassland surface increases nonlinearly with the increase of vegetation cover, and the increase of aerodynamic roughness is more obvious when the vegetation cover is more than 16% in the scope of this study. (3) Vegetation changed the typical jump-dominated wind–sand flow structure on the bare ground surface, showing a significant interception and attenuation effect of vegetation, which was manifested by the reduction of sand accumulation at the wind outlet and the increase of deposition within the vegetated area, thus effectively inhibiting the wind erosion process. The results of the study provide methodological references and a theoretical basis for the study of wind erosion along grassland highways in semi-arid regions and help to promote the sustainable development and ecological balance of grassland ecosystems in semi-arid regions. Full article

The fluctuating nature of renewable energy sources such as wind and solar power poses significant challenges to the stability of power grids, while pumped-storage hydropower, with its advantages in peak regulation and frequency control, has become an essential component of modern energy strategies. However, sediment in rivers adversely affects the operational efficiency and stability of PSH units, leading to accelerated wear and shortened service life. In this study, the low-pressure stage of a two-stage pump turbine was selected as the research object, and the Euler–Euler numerical method was employed to investigate the solid–liquid two-phase flow characteristics of the pump turbine in pump mode. The results show that, compared with the clear-water condition, the head and efficiency decrease by up to 7.9% and 15%, respectively, after the addition of sand particles. The average pressure within the flow-passage components increases, while the streamlines become more non-uniform, accompanied by the formation of vortices and backflow in the guide and return vanes. The total entropy generation increases with rising particle concentration but decreases with larger particle size. Among the components, the high-entropy regions are mainly located on the suction surface and trailing edges of the impeller blades, the inlet and blade surfaces of the guide vanes, and the inlet and trailing edges of the return vanes. Moreover, the pressure pulsation amplitudes at monitoring points in the vaneless region, guide vane–return vane interaction region, and leading edge of the return vane increase progressively with both particle size and concentration. The dominant and secondary frequencies at all monitoring points correspond to the blade-passing frequency (BPF) and its harmonics, indicating that rotor–stator interaction is the principal cause of pressure pulsations under pump operating conditions. Full article

To enhance the structural safety in wind-sand regions, this study employs the Euler-Lagrange numerical method to investigate the wind pressure characteristics of typical low-rise auxiliary buildings in a strong wind-blown sand environment. The results reveal that sand particle motion dissipates wind energy, leading to a slight reduction in average wind speed, while the increase in small-scale vortex energy enhances fluctuating wind speed. In the sand-laden wind field, the average wind pressure coefficient shows no significant change, whereas the fluctuating wind pressure coefficient increases markedly, particularly in the windward region of the building. Analysis of the skewness and kurtosis of wind pressure reveals that the non-Gaussian characteristics of wind pressure are amplified in the sand-laden wind, thereby elevating the risk of damage to the building envelope. Consequently, it is recommended that the design fluctuating wind load for envelopes and components of low-rise buildings in wind-sand regions be increased by 10% to enhance structural resilience. Full article

Due to the high sensitivity of grid-based micro-scale wind–sand flow models to deformation and distortion, this study employs the Smooth Particle Hydrodynamics (SPH) method for numerical simulations. The advantage of the SPH method is that it can dynamically analyze the entire trajectory of the particles, thus allowing the initial positional distribution of sand-buried particles to be traced. This study utilizes the advantages of the SPH method. It develops particle backtracking algorithms based on the SPH method using the C language. It analyses the initial location distribution, concentration, velocity, and particle size distribution of sand-buried particles to formulate targeted measures to cope with wind–sand disasters. Meanwhile, this paper improves a particle modeling algorithm to realize arbitrary mixing particle size and mixing ratio by programming in C language and combining it with pixel recognition technology. In addition, this paper will use the particle backtracking algorithm to analyze the classical embankment wind and sand flow field and then propose adequate measures for embankment wind and sand disaster management by investigating sand particle movement characteristics. Full article

A computational fluid dynamics (CFD) model of a railway culvert was established based on the two-phase flow theory to investigate wind-blown sand transport and sand sedimentation in and around a railway culvert. Then the flow field and the accumulation distribution of sand particles were analyzed through numerical simulation. The results show that the flow field around the culvert can be divided into deceleration, acceleration, and vortex areas. The curve of the horizontal wind speed along the central axis of the culvert had a W shape, indicating a significant increase in the wind speed inside the culvert. A large amount of sand accumulated at the culvert inlet because of the wing walls. The sand volume fraction in the culvert decreased with an increase in the inflow velocity, and there was almost no sand sedimentation when the inflow velocity was greater than 20 m/s. Three reasons for the sand accumulation in the culvert included the deflection by the wing walls, subgrade blocking, and a low inflow velocity. Based on the simulation results, straight and protruding culverts were designed to minimize sand accumulation. The straight culvert exhibited better performance than the protruding culvert and is recommended for use in railways. This work can provide theoretical support for designing railway culverts that minimize or prevent wind-blown sand accumulation. Full article

Windblown sand two-phase flow characteristics become an essential factor in evaluating the windblown sand load on infrastructures and civil structures. Based on the measured wind characteristics in arid desert regions, windblown sand flow fields with three kinds of sand beds are simulated in the wind tunnel, respectively. The results indicate that the characteristic saltation height of sand particles increases with the wind speed and particle size in the windblown sand flow field. As the sand concentration increases, the wind speed decreases, and the turbulence intensity increases. The concentration, energy, and impact pressure of sand particles increase with increasing wind speed and decrease exponentially with increasing height. At the same wind speed, the concentration, energy, and impact pressure of the coarse sand, fine sand, and mixed sand increases, in turn. Moreover, the variation of kinetic energy with height is similar to that of total energy with height and the proportion of potential energy to total energy is quite small. Full article

The local strong sandstorms (LSS), similar to haboobs in Sahara and the North America, often occur suddenly, in tens of minutes during the late afternoon, and before dusk in deserts in China, causing a significant impact on the local atmospheric environment. The Sudan haboob or American haboob often appears in the wet season, followed by thunderstorm events. In contrast, the LSS in China appears most frequently in relatively dry season. The lack of observational data in weather conditions before their formation, during their development and after their disappearance have hindered our understanding of the evolution mechanism of LSS/haboobs. This paper provides a review of the current status and model studies on LSS/haboobs in different time and space to characterize the weather conditions and triggering mechanisms for LSS/haboobs occurrence, as well as highlight the subject for further understanding of LSS/haboobs. LSS are always followed by the occurrence of a dry squall. The interaction of dust radiation heating in the near-surface mixing layer with a mesoscale anticyclone air mass (cold-air pool) in the upper layer is the key process that leads to an LSS. Haboobs are followed by the occurrence of a wet squall. The release of latent heat due to the condensation of water vapor, involving moist convection and cold downdraughts, is the main driving force that cause the occurrence of a haboob. For a better understanding of the characteristics of the wind-sand two-phase flow and the mechanism of energy dissipation in LSS/haboobs, further accumulation of meteorological observation data and small-scale multiple-phase numerical simulations are required. Full article

The scour phenomenon is critical for monopile structures in offshore wind farms. There are two possible strategies: allowing the development of scour holes around the monopile or avoiding it by placing scour protection. The last one is the most used up to now. This paper is focused on the determination of the weight of the stones forming the scour protection. There are some formulas for the design of these parameters, having a lot of uncertainties around them. Some of them were created for fluvial environment, with a different flow to the marine one. Other formulas were elaborated specifically for coastal structures, closer to the coast than offshore wind farms, and with dimensions completely different. This paper presents the analysis of three formulas: Isbash, corresponding to fluvial environment, and Soulsby, and De Vos, corresponding to marine environment. The results of the application of those formulas are compared with real data of scour protection systems showing good results in five offshore wind facilities in operation (Arklow Bank phase 1, Egmond aan Zee, Horns Rev phase 1, Princess Amalia, and Scroby Sands), giving conclusion about the uncertainties of the use of these formulas and recommendations for using them in offshore wind. Full article

This paper opens up a new perspective on the aerodynamic performance of a wind turbine airfoil. More specifically, the paper deals with a steady, incompressible two-phase flow, consisting of air and two different concentrations of sand particles, over an airfoil from the National Renewable Energy Laboratory, NREL S809. The numerical simulations were performed on turbulence models for aerodynamic operations using commercial computational fluid dynamics (CFD) code. The computational results obtained for the aerodynamic performance of an S809 airfoil at various angles of attack operating at Reynolds numbers of Re = 1 × 10⁶ and Re = 2 × 10⁶ in a dry, dusty environment were compared with existing experimental data on air flow over an S809 airfoil from reliable sources. Notably, a structured mesh consisting of 80,000 cells had already been identified as the most appropriate for numerical simulations. Finally, it was concluded that sand concentration significantly affected the aerodynamic performance of the airfoil; there was an increase in the values of the predicted drag coefficients, as well as a decrease in the values of the predicted lift coefficients caused by increasing concentrations of sand particles. The region around the airfoil was studied by using contours of static pressure and discrete phase model (DPM) concentration. Full article