| Wind-induced soil wind erosion has a negative impact on the ecology and human activities in arid and semi-arid areas,the scientific planting of planted windbreaks can effectively reduce the wind speed at ground level and inhibit the movement of soil particles in order to curb soil wind erosion.The porous media model theory has been applied several times to the study of soil wind erosion in recent years,and the accuracy of simulation test results using the resistance source term instead of the windbreak geometry model has received much attention.This thesis established a three-dimensional feature model with a similar appearance to artificial Caragana belts in the Siziwangqi region of Inner Mongolia.A combination of wind tunnel experiments and numerical simulations is used to analyze the feasibility of numerical simulations instead of wind tunnel experimental studies.To optimum design for planting Caragana belts in auxiliary wind-sand engineering,the porous media model was also used to predict the flow field characteristics and protection effects around large-scale Caragana belts with different configurations of row number,row spacing,plant spacing and arrangement.The main findings are as follows.(1)The Caragana belts canopy area is considered a porous medium in the experiment to establish a three-dimensional characteristic model based on the geometric similarity theorem.The turbulence control equations of the wind field are determined by the Reynolds averaging method based on the kinematic and dynamic similarity-defined boundary conditions.The porous medium model in Fluent can simulate the flow field distribution characteristics around the Caragana belts more accurately.In comparing the wind tunnel experiments and numerical simulation results of single-row and four-row Caragana belts,the relative standard deviation of wind velocity at more than 80% of the measured points is below the standard value of 5%.(2)The accuracy of the porous media model to simulate the aerodynamic properties of planted windbreaks is influenced by the model parameter settings and plant canopy structure.The errors in the simulation results of the Caragana belts are mostly found in the vortex region on the leeward side of the canopy,but the simulation of the large-scale Caragana belts can effectively reduce the influence of such errors on the calculation results of the porous media model.(3)The prediction of the field planting pattern of the Caragana belts windbreaks by the porous media model shows that the greater the row spacing,the worse the wind-blocking effect of the leeward side of the stand.The speed-reducing effect of the two rows of Caragana belts with 2H row spacing is the most obvious difference,and the wind-blocking effect of the two rows of Caragana belts with 8H row spacing is the same under the configuration of one-row-one-belt.The number of rows was positively correlated with the wind protection effect of the Caragana belts,and the wind protection effect of the one-row-two-belt Caragana belts combination was significantly higher than that of one-row-one-belt Caragana belts,but the difference with the wind protection effect of one-row-three-belt the Caragana belts combination was not significant.Plant spacing was negatively correlated with the wind-blocking effect of the Caragana belts,and the wind-blocking effect of the Caragana belts would be more obviously improved if the canopy layer between the Caragana belts overlapped.(4)The effective protection range of staggered and linear Caragana belts is significantly higher than that of matrix belts.From the perspective of soil wind erosion control and the joint ecological development of the study area,the staggered arrangement of two-row-one-belt of the Caragana belts in a group can better achieve the interception of surface wind speed.The optimum row spacing for the Caragana belts is 2H,the belts spacing is 8H,and the plant spacing is 1.75 H. |
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