Study On Protective Effect And Numerical Simulation Of Vertical PLA Sand Barrier

In this study,the bio degradable(PLA)sand barrier was used as the research material,and three vertical PLA sand barriers with different heights(50cm,70 cm and 100cm)were set as the research object.The wind speed and flow field were observed and the sediment transport was measured.Combined with the fluent numerical simulation method,the wind sand flow characteristics of the vertical PLA sand barrier under different design parameters were simulated,analyzed and supplemented to determine the protection effect of the sand barrier under different design parameters,It provides a theoretical basis for sand prevention and control in sandy areas.The main research results of this thesis are as follows:(1)The characteristics of wind speed and flow field of vertical PLA sand barrier at three heights are mainly "single peak",the change is mainly "lifting acceleration deceleration recovery",and there is an inflection point at 1m behind the barrier.The deceleration zones formed after the 100 cm vertical PLA sand barrier are 5.3m,4.2m and3.8m respectively,which are significantly higher than the other two height sand barriers,and the range of deceleration zone gradually decreases with the increase of wind speed.(2)The sediment transport capacity of vertical PLA sand barrier with different heights decreases gradually with the increase of height,and the sediment transport capacity is concentrated in the range of 0 ～ 10 cm height.The sediment transport capacity of vertical PLA sand barrier with height of 100 cm is significantly lower than that of vertical PLA sand barrier with other two heights.After analyzing the sand particle size characteristics of aeolian sand flow in front of and behind the sand barrier,the content of fine sand behind the barrier is higher than that before the barrier,and the content is more than 80%,With the increase of sand barrier height,the sand carrying capacity of wind blown sand flow becomes stronger.(3)Under different design parameters,the wind speed flow field of the vertical PLA sand barrier is divided into five areas: the resistance lifting area in front of the barrier,the acceleration area at the top of the barrier,the deceleration area between the barriers,the weak wind area behind the barrier and the wind speed recovery area.From the form of the wind speed profile in the vertical direction,it is mainly in the form of "s" and logarithmic function.From the change of the wind speed in the horizontal direction,it is mainly in the form of "W" and "V".From the simulation of sand accumulation,with the increase of the number of rows of sand barrier,the weakening effect of wind speed is more obvious,and the more sand is accumulated.With the increase of the height of sand barrier,the more sand is concentrated near the second sand discharge barrier.(4)Through the comprehensive analysis of the field test and numerical simulation results,it is concluded that although the single row vertical PLA sand barrier can effectively reduce the surface wind speed and reduce the sediment transport,when the air flow crosses the sand barrier,it will soon return to the wild wind speed,and the protection distance is very limited.Through simulation,the optimal porosity of sand barrier is 30 ～40% and the height of sand barrier is controlled between 120 ～ 150 cm.The layout principle of "horizontal multi row laying" should be adopted,which can make the wind speed decrease step by step and better control the movement of sand particles,so as to give better play to the role of wind prevention and sand fixation of vertical PLA sand barrier.