Wind Tunnel Experiment Study On The Mechanism Of Windbreak And Sand Blocking Of A Backward Elevated Sand Barrier

The principle of backward facing sand barrier is to form a backward facing angle with the ground on the basis of traditional vertical sand barriers,in order to weaken the airflow behind the barrier,lift and accelerate the airflow above the sand barrier.This study adopts wind tunnel simulation to study the wind speed,sediment transport and sediment distribution around 60°and 45°backward facing sand barriers under different wind direction angles.By comparing with traditional high standing sand barriers,the better backward facing sand barriers are selected and applied to wind erosion pits using Fluent numerical simulation method to explore the effect of backward facing sand barriers on wind erosion pits,providing theoretical basis and technical support for the laying of sand barriers and field experiments.The main research conclusions are as follows:（1）Under different wind directions and angles,the 45°backward facing sand barrier has a significant lifting effect on the upper airflow,and the range of action is relatively large.When the wind direction angle is 45°and 90°,the backward sand barrier has a significant weakening effect on the airflow behind the barrier.The range of weak wind zones in the 60°backward sand barrier increased by 0.5 H and 2 H respectively compared to the vertical barrier,and the minimum wind speed decreased by 0.17 m·s^-1and 0.04 m·s^-1respectively compared to the vertical barrier.The range of weak wind zone in the 45°backward facing sand barrier increased by 1 H and 0.5 H respectively compared to the vertical type,and the minimum wind speed decreased by 0.02 m·s^-1and0.03 m·s^-1respectively compared to the vertical type.As the wind speed increases,the distance of the effect range on airflow uplift gradually increases,and the distance of the weak wind zone formed behind the obstacle gradually increases.（2）The back facing sand barrier changed the trajectory of surface wind and sand flow,effectively interceptsd sand particles in the surface wind and sand flow.Under different wind directions and angles,the 60°rear elevation sand barrier has a significant sand blocking effect,with a 26.50%to 84.65%decrease in sediment transport compared to the upright position.The 45°back facing sand barrier has a significant sand blocking effect only when the wind direction angle is 90°,and the sediment transport behind the barrier is reduced by 82.30%compared to the vertical type.（3）When the wind direction angle is 45°and 75°,the sand accumulation effect behind the backward facing sand barrier is significant,and more sand materials are unloaded and accumulated away from the rear of the sand barrier.When the wind direction angle is 45°,the sand accumulation effect of the two types of sand barriers is the most obvious.Compared with the vertical type,the sand accumulation range and volume of the upward type sand barrier after 60°increased by 0.5 m and 2843.90 cm³.The sand accumulation volume increased by 2062.34 cm³for a 45°backward sand barrier.（4）The rear facing sand barrier is set up in the wind erosion pit,forming a clear deceleration zone in front of and behind the barrier.The airflow passing through the top of the sand barrier tilts upwards,causing the high-speed airflow area to rise and move around the rear wall,directly acting on the sand accumulation body.