Study On The Mechanism Of Wind Erosion Of Desertification Grassland Soils By Shrub Configuration Patterns

Sand control is crucial in constructing an ecological security barrier in northern China.The scientific configuration of forest and grass vegetation types and densities is a primary challenge in ecological protection and restoration.Windbreaks serve as a cost-effective and efficient means of rapid surface restoration,predominantly employed for afforestation in northern China’s arid and semi-arid regions.However,the effectiveness of windbreaks and the mechanisms of soil erosion between stands remain uncertain in the degraded grassland.Further research on its wind and sand transport mechanism is needed as an important reference basis for Caragana belt planting.This study integrates two-phase flow aerodynamics,porous media percolation mechanics,and soil mechanics theories to unveil the wind speed distribution and wind erosion inhibition efficiency among Caragana belts.The objective is to determine an optimal configuration scale for Caragana belts.In this research,the Caragana belts forest in the desert grassland of the Siziwang county area in the Inner Mongolia Autonomous Region was chosen as the subject.The study considers factors of Caragana belts and their planting engineering scale configuration,intending to analyze the impact of artificially established Caragana belt on wind and sand flow movement and their control mechanisms.This research aims to enhance the suppression of soil wind erosion by Caragana belts while minimizing the impact on the natural environment and capital investment.Conclusions derived from this study are as follows:(1)Wind tunnel experiments were carried out to collect data on the wind field distribution of Caragana belts with varying arrangements,central wind speeds,and measurement points.This data offers reliable support for simulation experiments.The results demonstrate that utilizing the porous media model alternative the wind tunnel experiments for wind protection studies involving planted windbreak belts is accurate and feasible,given that principle of similarity is satisfied.Comparisons of wind speed distributions for single and four-row Caragana belts reveal a high degree of agreement between simulation and wind tunnel experiments.At central wind speeds of 6,9,and 12m/s,over 80% of the measurement points exhibited a relative standard deviation(RSD)of less than 5%,with a maximum wind speed error of only 0.257 m/s at the highest RSD value.(2)By optimizing the wind speed sensor of the wind profile equipment,results with enhanced resolution and output stability for wide range of airflow velocities can be achieved.The sensor can respond effectively to ambient temperature changes of-10 to30°C.Moreover,the power function correction method offers highly efficient temperature compensation for the thermal air velocity sensor,with the corrected air velocity measurement error being less than 5%.These optimization measures enable the wind speed profiler to fulfill the requirements for near-surface wind speed profile data acquisition in the field work.Based on the principle of double-column bypass characteristics and friction loss,a double-column bypass friction type wind and sand separator is designed.The sand sampler was tested by computational fluid dynamics(CFD)and verified in a wind tunnel with an average gas-solid separation efficiency of98.9%,an isokinetic property of 92.93%,and a sand collection efficiency greater than 90%in the wind speed range of 9 ～ 18 m/s.Its average sand collection efficiency was 90.32%.(3)The critical parameters of the porous media model were calculated to predict the optimal configuration scale of the Caragana belts.The prediction experiment showed that staggered and straight rows provided effective Wind and sand barrier effect with minor differences.Staggered Caragana belts allowed each Caragana plant more growth space,enhancing nutrient absorption and ecological performance.The findings indicate that arranging two rows of Caragana belts as a belt with two rows provides better wind protection with the same number of plants,with a row spacing of 2H and a strip spacing of 8H.Planting more than two belts can achieve this protection.For a single Caragana,the ideal configuration consists of a height of at least 1m and a porosity of 65%.Based on the dense planting of Caragana plants,it is recommended that the plant spacing be set at1.75 H to maximize the overall wind protection effectiveness of the Caragana plants under proper planting.Furthermore,five different wind directions were tested,and the results indicated that at different wind directions the optimal scale of the Caragana belt had a significant effect on the area of effective protection area behind the Caragana belts.When the wind direction was perpendicular to the planting direction of the Caragana belt,the percentage of protected area behind the belt was the largest(68.46%),and when parallel,the percentage of protected area was the smallest(25.98%).(4)By comparing unprotected and desert grasslands,tilled surfaces,scattered Caragana belts,and row strip planting Caragana areas,it was found that the row strip planting method with a higher cover rate that had not reached maturity can minimized wind erosion of the whole block.The study of the inter-belt soils revealed that planting density influenced the soil water content and nutrient and organic matter changes.The inter-belt soil water content exhibited an "ω" shape.The analysis of the inter-row belts showed that 52.96% of the soils had a diameter of <0.25 mm.