Wind Tunnel Measurements of Surface Shear Stress on an Isolated Dune Downwind a Bridge

Abstract

As part of a comprehensive environmental assessment of the Dun-Gel railway project located in Dunhuang city, Gansu Province, China, a wind tunnel experiment was proposed to predict surface shear stress changes on a sand dune when a bridge was built upstream it. The results show that the length of the wall shear stress shelter region of a bridge is about 10 times of the bridge height (H). In the cases that the interval of the bridge and sand dune (S) is less than 5 H, normalized wall shear stress on the windward crest is decreased from 1.75 (isolated dune) to 1.0 (S = 5.0 H, measured downwind bridge pier) and 1.5 (S = 5.0 H, measured in the middle line of two adjacent bridge piers). In addition, the mean surface shear stress in the downstream zone of the sand dune model is reduced by the bridge pier and is increased by the bridge desk. As for the fluctuation of surface shear stress ( ζ ) on the windward crest, ζ decreases from 1.3 (in the isolated dune case) to 1.2 (in the case S = 5.0 H, measured just downwind the pier) and increases from 1.3 (in the isolated dune case) to 1.6 (in the cases S = 5.0 H, in the middle of two adjacent piers). Taking the mean and fluctuation of surface shear stress into consideration together, we introduce a parameter ψ ranging from 0 to 1. A low value indicates deposition and a high value indicates erosion. On the windward slope, the value of ψ increases with height (from 0 at toe to 0.98 at crest). However, in the cases of S = 1.5 H, ψ is decreased by the bridge in the lower part of the sand dune at y = 0 and is increased at y = L/2 compared with the isolated dune case. In other cases, the change of ψ on the windward slope is not as prominent as in the case of S = 1.5 H. Downstream the sand dune, erosion starts in a point that exists between x = 10 H and 15 H in all cases.

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

“…In the wind speed acceleration zone at the subgrade windward slope shoulder, the key point for the prevention and control of wind-blown sand hazards is to adopt gravel wrapping slopes and widening measures to prevent wind-blown sand flow erosion of subgrade embankment. In this wind tunnel experiment, the changes in the wind speed on the subgrade top and its windward and leeward directions are similar to relevant research results [ 43 , 44 , 45 ].…”

Comparison of Protective Measures Against Wind Blown Sand on Railway

“…The basic functions of the wind blown sand control project can be summarized as follows: The first is the inhibition of sand initiation; The second is the control of surface wind erosion; The third is the strengthening of the movement of wind sand flow; The fourth is to reduce the wind speed and force the deposition of wind sand flow; The fifth is to control the direction of sand flow artificially; The sixth is to change the overall wind sand flow movement into the dispersed wind sand flow movement. According to these classifications, the corresponding mechanical principles of wind sand protection can be summarized as the following six points: (1) Isolate the contact between gas and solid at the interface; (2) restrain the interaction (coherence) between gas and solid at the interface; (3) increase the local resistance of wind sand fluid movement; (4) reduce and overcome the resistance along the way and local resistance of wind sand fluid; (5) guide the wind blown sand fluid to change direction; (6) reduce and eliminate various resistance of sand dunes in the process of propulsion [1][2][3][4][5][6][7][8][9].…”

Cellular automaton modelling of the effects of buildings on aeolian bedform dynamics

“…As unerodable, bluff objects, buildings change the wind field in their surroundings (Hunt, 1971;Nordstrom and McCluskey, 1985), create patterns of erosion and deposition (Luo et al, 2012;Poppema et al, 2021), and act as an obstacle to sediment transport (Jackson and Nordstrom, 2011). Cities, bridges and other infrastructure in deserts and dune fields have also been shown to alter wind speed, wind direction, sediment transport capacity, and vegetation cover in their surroundings, and can cut off dune fields from their sediment source (Malvarez et al, 2013;Hernández-Calvento et al, 2014;Smith et al, 2017b;Bruno et al, 2018;Wang et al, 2020).…”