Fetch effect on the developmental process of aeolian sand transport in a wind tunnel  

作　　者：CHEN Zongyan XIAO Fengjun DONG Zhibao 

机构地区：[1]School of Geography and Tourism,Shaanxi Normal University,Xi'an 710119,China [2]College of Geographic Science,Qinghai Normal University,Xining 810008,China

出　　处：《Journal of Arid Land》2020年第3期436-446,共11页干旱区科学（英文版）

基　　金：supported by the National Natural Science Foundation of China (41601002, 41871011);the China Postdoctoral Science Foundation (2017M623115);the Science Foundation of Shaanxi Province (2018JQ4010);the Fundamental Research Funds for the Central Universities (GK201903077)

摘　　要：As the sand mass flux increases from zero at the leading edge of a saltating surface to the equilibrium mass flux at the critical fetch length,the wind flow is modified and then the relative contribution of aerodynamic and bombardment entrainment is changed.In the end the velocity,trajectory and mass flux profile will vary simultaneously.But how the transportation of different sand size groups varies with fetch distance is still unclear.Wind tunnel experiments were conducted to investigate the fetch effect on mass flux and its distribution with height of the total sand and each size group in transportation.The mass flux was measured at six fetch length locations(0.5,1.2,1.9,2.6,3.4 and 4.1 m)and at three free-stream wind velocities(8.8,12.2 and 14.5 m/s).The results reveal that the total mass flux and the mass flux of each size group with height can be expressed by q=aexp(–bh),where q is the sand mass flux at height h,and a and b are regression coefficients.The coefficient b represents the relative decay rate.Both the relative decay rates of total mass flux and each size group are independent of fetch length after a quick decay over a short fetch.This is much shorter than that of mass flux.The equilibrium of the relative decay rate cannot be regarded as an equilibrium mass flux profile for aeolian sand transport.The mass fluxes of 176.0,209.3 and 148.0μm size groups increase more quickly than that of other size groups,which indicates strong size-selection of grains exists along the fetch length.The maximal size group in mass flux(176.0μm)is smaller than the maximal size group of the bed grains(209.3μm).The relative contribution of each size group to the total mass flux is not monotonically decreasing with grain size due to the lift-off of some small grains being reduced due to the protection by large grains.The results indicate that there are complex interactions among different size groups in the developmental process of aeolian sand transport and more attention should be focused on the fetch effect because

关 键 词：fetch length mass flux profile grain size distribution sand transport wind tunnel experiment 

分 类 号：P931.3[天文地球—自然地理学]