Wind Tunnel Test on Windblown Sand Two-Phase Flow Characteristics in Arid Desert Regions

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.

Unified model of sediment transport threshold and rate across subaqueous bedload, windblown sand, and windblown snow

<p>Nonsuspended sediment transport (NST) refers to the sediment transport regime in which the flow turbulence is unable to support the weight of transported grains. It occurs in fluvial environments (i.e., driven by a stream of liquid) and in aeolian environments (i.e., wind-blown) and plays a key role in shaping sedimentary landscapes of planetary bodies. NST is a highly fluctuating physical process because of turbulence, surface inhomogeneities, and variations of grain size and shape and packing geometry. Furthermore, the energy of transported grains varies strongly due to variations of their flow exposure duration since their entrainment from the bed. In spite of such variability, we here propose a deterministic model that represents the entire grain motion, including grains that roll and/or slide along the bed, by a periodic saltation motion with rebound laws that describe an average rebound of a grain after colliding with the bed. The model simultaneously captures laboratory and field measurements and discrete element method (DEM)-based numerical simulations of the threshold and rate of equilibrium NST within a factor of about 2, unifying weak and intense transport conditions in oil, water, and air (oil only for threshold). The model parameters have not been adjusted to these measurements but determined from independent data sets. Recent DEM-based numerical simulations (Comola, Gaume, et al., 2019, https://doi.org/10.1029/2019GL082195) suggest that equilibrium aeolian NST on Earth is insensitive to the strength of cohesive bonds between bed grains. Consistently, the model captures cohesive windblown sand and windblown snow conditions despite not explicitly accounting for cohesion.</p>

Characterization of windblown sand transport in open field conditions through wind-sand tunnel testing and computational simulation

<p>Aeolian sediment transport in desert and sandy coastal environments affects civil structures and infrastructures, such as pipelines, industrial facilities, towns, single buildings, farms, roads, and railways [1]. The wind flow interacts with surface-mounted obstacles of any kind inducing sand erosion, transport, and sedimentation around them. This can lead to detrimental effects such as the loss of functionality of the endangered structure or infrastructure, or even danger for users when structural failure is involved [2]. In order to cope with the effects above, the demand for the characterization of aeolian sand transport and the design of Sand Mitigation Measures (SMMs) has grown in the last decade and is expected to further increase in the next years [1]. The multiphase and multiscale nature of the aeolian flow ranging from the sand grain diameters to the obstacle characteristic lengths make the problem only tractable by means of physical experiments and computational simulations. On the one hand, in-situ full scale field tests are expensive, time-consuming, and subject to environmental setup conditions difficult to control. On the other hand, numerical models shall be carefully validated against physical experiments. Hence, experimental Wind-Sand Tunnel Tests (WSTTs) are often carried out.</p><p>In this study, windblown sand transport on flat ground is reproduced by means of WSTTs carried out in the wind tunnel L-1B of von Karman Institute for Fluid Dynamics. The aim of WSTTs is twofold. On one hand, they are intended to characterize the incoming sand flux in open field conditions. On the other hand, they allow to properly tune cheaper Wind-Sand Computational Simulations [3], so as to assess the performance of SMMs in full-scale. The wind tunnel setup implements a uniform 5-meter-long sand fetch as sand source. The wind speed boundary layer and sand flux saltation layer are characterized through 2D Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) techniques, respectively. Wind flow and sand transport state variables are assessed along the sand fetch by setting the wind speed equal to 1.3, 1.5, 2 times the threshold one, and by assessing the influence of a monoplane grid installed at the inlet of the wind tunnel testing sections. Results from WSTTs are critically discussed by investigating the effects induced by the sand fetch length, wind speed, and turbulence intensity on the sand transport. Finally, a Eulerian multiphase computational fluid dynamics model is tuned in order to reproduce the obtained results.</p><p><strong>References</strong></p><p>[1] Bruno L, Horvat M, Raffaele L. Windblown sand along railway infrastructures: a review of challenges and mitigation measures. J Wind Eng Ind Aerodynam 2018;177:340–65.<br>[2] Raffaele L, Bruno L. Windblown sand action on civil structures: Definition and probabilistic modelling. Eng Struct 2019;178:88-101.<br>[3] Lo Giudice A, Preziosi L. A fully Eulerian multiphase model of windblown sand coupled with morphodynamic evolution: Erosion, transport, deposition, and avalanching. Appl Math Model 2020;79:68-84.</p>

Windblown Sand-Induced Degradation of Glass Panels in Curtain Walls

The windblown sand-induced degradation of glass panels influences the serviceability and safety of these panels. In this study, the degradation of glass panels subject to windblown sand with different impact velocities and impact angles was studied based on a sandblasting test simulating a sandstorm. After the glass panels were degraded by windblown sand, the surface morphology of the damaged glass panels was observed using scanning electron microscopy, and three damage modes were found: a cutting mode, smash mode, and plastic deformation mode. The mass loss, visible light transmittance, and effective area ratio values of the glass samples were then measured to evaluate the effects of the windblown sand on the panels. The results indicate that, at high abrasive feed rates, the relative mass loss of the glass samples decreases initially and then remains steady with increases in impact time, whereas it increases first and then decreases with an increase in impact angle such as that for ductile materials. Both visible light transmittance and effective area ratio decrease with increases in the impact time and velocities. There exists a positive linear relationship between the visible light transmittance and effective area ratio.