The main factors influencing soil erosion include the net rain excess, the water depth, the velocity, the shear stress of overland flows, and the erosion-resisting capacity of soil. The laws of these factors varying w...The main factors influencing soil erosion include the net rain excess, the water depth, the velocity, the shear stress of overland flows, and the erosion-resisting capacity of soil. The laws of these factors varying with the slope gradient were investigated by using the kinematic wave theory. Furthermore, the critical slope gradient of erosion was driven. The analysis shows that the critical slope gradient of soil erosion is dependent on grain size, soil bulk density, surface roughness, runoff length, net rain excess, and the friction coefficient of soil, etc. The critical slope gradient has been estimated theoretically with its range between 41.5 degrees similar to 50 degrees.展开更多
Slope variation will significantly affect the characteristics of the wind field around a hill.This paper conducts a large-eddy simulation(LES)on an ideal 3D hill to study the impact of slope on wind field properties.E...Slope variation will significantly affect the characteristics of the wind field around a hill.This paper conducts a large-eddy simulation(LES)on an ideal 3D hill to study the impact of slope on wind field properties.Eight slopes ranging from 10°to 45°at 5°intervals are considered,which covers most conventional hill slopes.The inflow turbulence for the LES is generated by adopting a modified generation method that combines the equilibrium boundary conditions with the Fluent inherent vortex method to improve the simulation accuracy.The time-averaged flow field and the instantaneous vortex structure under the eight slopes are comparatively analyzed.The accuracy of the present method is verified by comparison with experimental data.The slope can affect both the mean and fluctuating wind flow fields around the 3D hill,especially on the hilltop and the leeward side,where a critical slope of 25°can be observed.The fluctuating wind speeds at the tops of steep hills(with slope angles beyond 25°)decrease with increasing slope,while the opposite phenomenon occurs on gentle hills.With increasing slope,the energy of the high-speed descending airflow is enhanced and pushes the separated flow closer to the hill surface,resulting in increased wind speed near the wall boundary on the leeward side and inhibiting the development of turbulence.The vortex shedding trajectory in the wake region becomes wider and longer,suppressing the growth of the mean wind near the wall boundary and enhancing the turbulence intensity.展开更多
In this paper,the process of wind erosion on two kinds of soil from the agro-pastoral area of Inner Mongolia are studied using wind tunnel experiments,considering the wind speed,blown angle of wind and soil moisture c...In this paper,the process of wind erosion on two kinds of soil from the agro-pastoral area of Inner Mongolia are studied using wind tunnel experiments,considering the wind speed,blown angle of wind and soil moisture content.The results showed that the modulus of soil wind erosion increases with an increase of wind speed.When the wind speed exceeds a critical value,the soil wind erosion suddenly increases.The critical speed for both kinds of soil is within the range of 7-8m·s-1.For a constant wind speed,the rate of soil wind erosion changes from increasing to falling at a critical soil slope.The critical slope of loam soil and sandy loam soil is 20° and 10°,respectively.Soil moisture content has a significant effect on wind erosion.Soil wind erosion of both soils decreases with an increase of the soil water content in two treatments,however,for treatment two,the increasing trends of wind erosion for two soils with the falling of soil water content are no significant,especially for the loam soil,and in the same soil water content,the wind erosion of two soils in treatment one is significantly higher than treatment two,this indicates reducing the disturbance of soil surface can evidently control the soil wind erosion.展开更多
Complicated terrain was considered and simplified as two-dimensional(2D)terrain in a dynamical downscaling model and a parametric wind field model for typhoons developed by the Shanghai Typhoon Institute.The 2D terrai...Complicated terrain was considered and simplified as two-dimensional(2D)terrain in a dynamical downscaling model and a parametric wind field model for typhoons developed by the Shanghai Typhoon Institute.The 2D terrain was further modeled as uphill and downhill segments with various slope angles relative to the incoming flow.The wind speed ratios and pressure characteristics around the 2D terrain were numerically and experimentally investigated in this study.Aerodynamic characteristics of the 2D terrain with a limitedlength upper surface were first investigated in the wind tunnel with sheared incoming flow.The corresponding numerical investigation was also conducted by using the commercial computational fluid dynamics code FLUENT with the realizable k-ε turbulence model.Special efforts were made to maintain the inflow boundary conditions throughout the computational domain.Aerodynamic characteristics were then investigated for the ideal 2D terrain with an unlimited-length upper surface by using a numerical method with uniform incoming flow.Comparisons of the different terrain models and incoming flows from the above studies show that the wind pressure coefficients and the wind speed ratios are both affected by the slope angle.A negative peak value of the wind pressure coefficients exists at the escarpment point,where flow separation occurs,for the uphill and downhill terrain models with slope angles of 40°and 30°,respectively.Correspondingly,the streamwise wind speed ratios at the points above the escarpment point for the uphill terrain model increase with increasing slope angle,reach their peak values at the slope angle of a=40°and decrease when the slope angle increases further.For the downhill terrain model,similar trends exist at the points above the escarpment point with the exception that the critical slope angle is a=30°.展开更多
文摘The main factors influencing soil erosion include the net rain excess, the water depth, the velocity, the shear stress of overland flows, and the erosion-resisting capacity of soil. The laws of these factors varying with the slope gradient were investigated by using the kinematic wave theory. Furthermore, the critical slope gradient of erosion was driven. The analysis shows that the critical slope gradient of soil erosion is dependent on grain size, soil bulk density, surface roughness, runoff length, net rain excess, and the friction coefficient of soil, etc. The critical slope gradient has been estimated theoretically with its range between 41.5 degrees similar to 50 degrees.
基金supported by the National Key R&D Plan of China(No.2018YFB1501104)the National Natural Science Foundation of China(Grant No.52278511)+1 种基金the Natural Science Foundation of Hebei Province(No.E2021210053)the Young Backbone Teacher Cultivation Program of Henan University of Technology.
文摘Slope variation will significantly affect the characteristics of the wind field around a hill.This paper conducts a large-eddy simulation(LES)on an ideal 3D hill to study the impact of slope on wind field properties.Eight slopes ranging from 10°to 45°at 5°intervals are considered,which covers most conventional hill slopes.The inflow turbulence for the LES is generated by adopting a modified generation method that combines the equilibrium boundary conditions with the Fluent inherent vortex method to improve the simulation accuracy.The time-averaged flow field and the instantaneous vortex structure under the eight slopes are comparatively analyzed.The accuracy of the present method is verified by comparison with experimental data.The slope can affect both the mean and fluctuating wind flow fields around the 3D hill,especially on the hilltop and the leeward side,where a critical slope of 25°can be observed.The fluctuating wind speeds at the tops of steep hills(with slope angles beyond 25°)decrease with increasing slope,while the opposite phenomenon occurs on gentle hills.With increasing slope,the energy of the high-speed descending airflow is enhanced and pushes the separated flow closer to the hill surface,resulting in increased wind speed near the wall boundary on the leeward side and inhibiting the development of turbulence.The vortex shedding trajectory in the wake region becomes wider and longer,suppressing the growth of the mean wind near the wall boundary and enhancing the turbulence intensity.
基金supported by Key Program of National Natural Science Foundation of China(Grant No. 41130744)China National Natural Science Foundation (Grant No. 40971165)State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau open Foundation(Grant No. 10501-1220)
文摘In this paper,the process of wind erosion on two kinds of soil from the agro-pastoral area of Inner Mongolia are studied using wind tunnel experiments,considering the wind speed,blown angle of wind and soil moisture content.The results showed that the modulus of soil wind erosion increases with an increase of wind speed.When the wind speed exceeds a critical value,the soil wind erosion suddenly increases.The critical speed for both kinds of soil is within the range of 7-8m·s-1.For a constant wind speed,the rate of soil wind erosion changes from increasing to falling at a critical soil slope.The critical slope of loam soil and sandy loam soil is 20° and 10°,respectively.Soil moisture content has a significant effect on wind erosion.Soil wind erosion of both soils decreases with an increase of the soil water content in two treatments,however,for treatment two,the increasing trends of wind erosion for two soils with the falling of soil water content are no significant,especially for the loam soil,and in the same soil water content,the wind erosion of two soils in treatment one is significantly higher than treatment two,this indicates reducing the disturbance of soil surface can evidently control the soil wind erosion.
基金The authors grateftilly acknowledge the support of the Ministry of Science and Technology of China(Grant Nos.2015CB452806 and 2018YFB1501104)the National Natural Science Foundation of China(Grant Nos.51408196 and 41805088)+1 种基金the Natural Science Foundation of Shanghai(Grant No.19ZR1469200)the Young Backbone Teacher Cultivation Program of Henan University of Technology.
文摘Complicated terrain was considered and simplified as two-dimensional(2D)terrain in a dynamical downscaling model and a parametric wind field model for typhoons developed by the Shanghai Typhoon Institute.The 2D terrain was further modeled as uphill and downhill segments with various slope angles relative to the incoming flow.The wind speed ratios and pressure characteristics around the 2D terrain were numerically and experimentally investigated in this study.Aerodynamic characteristics of the 2D terrain with a limitedlength upper surface were first investigated in the wind tunnel with sheared incoming flow.The corresponding numerical investigation was also conducted by using the commercial computational fluid dynamics code FLUENT with the realizable k-ε turbulence model.Special efforts were made to maintain the inflow boundary conditions throughout the computational domain.Aerodynamic characteristics were then investigated for the ideal 2D terrain with an unlimited-length upper surface by using a numerical method with uniform incoming flow.Comparisons of the different terrain models and incoming flows from the above studies show that the wind pressure coefficients and the wind speed ratios are both affected by the slope angle.A negative peak value of the wind pressure coefficients exists at the escarpment point,where flow separation occurs,for the uphill and downhill terrain models with slope angles of 40°and 30°,respectively.Correspondingly,the streamwise wind speed ratios at the points above the escarpment point for the uphill terrain model increase with increasing slope angle,reach their peak values at the slope angle of a=40°and decrease when the slope angle increases further.For the downhill terrain model,similar trends exist at the points above the escarpment point with the exception that the critical slope angle is a=30°.
