风沙流起动阶段沙粒输运特征
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摘要
为了探究风沙流起动过程中沙粒输运特征,利用PTV测量技术在风洞中对风沙流起动过程进行了测量,分析了沙粒空间分布、沙粒平均水平速度、输沙率、沙粒数密度和输沙通量随时间的变化规律。结果表明:风沙流起动时间大约为1.5s。起动过程中,输沙率随时间迅速增加,气流中沙粒总数目随时间的变化可表示为指数函数,沙粒数密度和输沙通量随高度的变化均可近似表示为负指数衰减函数。在t=1.0s时刻的沙粒平均水平速度大于相同高度处以后时刻的沙粒平均水平速度,同一高度处t=1.5s以后的沙粒数密度大于t=0.5s、1.0s时刻的沙粒数密度,同一高度处t=1.5s以后的输沙通量大于t=1.0s时刻的输沙通量。沙粒数密度随高度的衰减率一般随时间的增加而减小,并在t=1.5s后逐渐接近稳定值。
In order to further explore the characteristics of sand transport during the initiation process of aeolian sand transport,the developing process of initiation of aeolian sand transport was measured by PTV(particle tracking velocimetry)technology in a wind tunnel.The variation of particle space distribution,the horizontal particle velocity,sand transport rate,particle number density and sand flux with time is analyzed.The result shows that the time consumption is about 1.5 s for the initiation process of aeolian sand transport.During the initiation process,the sand transport rate increases rapidly with time,the total particle number in air increases exponentially with time,and the variation of both particle number density and sand flux with height can be approximately expressed by a negative exponential function.At the same height,the mean horizontal particle velocity at t=1.0 s is larger than that after this time,the particle number density after t=1.5 s is larger than that at t=0.5 s and 1.0 s,and the sand flux after t=1.5 s is more than that at t=1.0 s.The decay rate of particle number density with height generally decreases with time,and approximates to a constant after t=1.5 s.
In order to further explore the characteristics of sand transport during the initiation process of aeolian sand transport,the developing process of initiation of aeolian sand transport was measured by PTV(particle tracking velocimetry)technology in a wind tunnel.The variation of particle space distribution,the horizontal particle velocity,sand transport rate,particle number density and sand flux with time is analyzed.The result shows that the time consumption is about 1.5 s for the initiation process of aeolian sand transport.During the initiation process,the sand transport rate increases rapidly with time,the total particle number in air increases exponentially with time,and the variation of both particle number density and sand flux with height can be approximately expressed by a negative exponential function.At the same height,the mean horizontal particle velocity at t=1.0 s is larger than that after this time,the particle number density after t=1.5 s is larger than that at t=0.5 s and 1.0 s,and the sand flux after t=1.5 s is more than that at t=1.0 s.The decay rate of particle number density with height generally decreases with time,and approximates to a constant after t=1.5 s.
引文
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[2]Zou X Y,Wang Z L,Hao Q Z,et al.The distribution of velocity and energy of saltating sand grains in a wind tunnel[J].Geomorphology,2001,36:155-165.
[3]Dong Z B,Liu X P,Wang H T,et al.Aeolian sand transport:a wind tunnel model[J].Sedimentary Geology,2003,161:71-83.
[4]Liu X P,Dong Z B.Experimental investigation of the concentration profile of a blowing sand cloud[J].Geomorphology,2004,60:371-381.
[5]Kang L Q,Zhao G D,Zou X Y,et al.An improved particle counting method for particle volume concentration in aeolian sand transport[J].Powder Technology,2015,280:191-200.
[6]Kang L Q,Guo L J,Liu D Y.Reconstructing the vertical distribution of the aeolian saltation mass flux based on the probability distribution of lift-off velocity[J].Geomorphology,2008,96:1-15.
[7]Butterfield G R.Transitional behaviour of saltation:wind tunnel observations of unsteady winds[J].Journal of Arid Environments,1998,39:377-394.
[8]赵国丹,亢力强,邹学勇,等.稳态风沙流中沙粒体积浓度的模型分析[J].中国沙漠,2015,35(5):1113-1119.
[9]Davidson-Arnott R G D,MacQuarrie K,Aagaard T.The effect of wind gusts,moisture content and fetch length on sand transport on a beach[J].Geomorphology,2005,68:115-129.
[10]Ellis J T,Sherman D J,Farrell E J,et al.Temporal and spatial variability of aeolian sand transport:implications for field measurements[J].Aeolian Research,2012,3:379-387.
[11]Davidson-Arnott R G D,Bauer B O,Walker I J,et al.Highfrequency sediment transport responses on a vegetated foredune[J].Earth Surface Processes and Landforms,2012,37:1227-1241.
[12]Anderson R S,Haff P K.Simulation of eolian saltation[J].Science,1988,241:820-823.
[13]Anderson R S,Haff P K.Wind modification and bed response during saltation of sand in air[M]//Barndorff-Nielsen O E,Willetts B B.Aeolian Grain Transport 1.Acta Mechanica Supplementum.Vienna,Austria:Springer,1991:21-51.
[14]Spies P-J,McEwan I K,Butterfield G R.One-dimensional transitional behaviour in saltation[J].Earth Surface Processes and Landforms,2000,25:505-518.
[15]Kang L Q,Guo L J.Eulerian-Lagrangian simulation of aeolian sand transport[J].Powder Technology,2006,162(2):111-120.
[16]Tong D,Huang N.Numerical simulation of saltating particles in atmospheric boundary layer over flat bed and sand ripples[J].Journal of Geophysical Research,2012,117:D16205.
[17]Zheng X J,Huang N,Zhou Y.The effect of electrostatic force on the evolution of sandsaltation cloud[J].European Physical Journal E,2006,19:129-138.
[18]Al-awadhi J M,Willetts B B.Transient sand transport rates after wind tunnel start-up[J].Earth Surface Processes and Landforms,1998,22:21-30.
[19]Dong Z B,Qian G Q,Luo W Y,et al.Analysis of the mass flux profiles of an aeolian saltating cloud[J].Journal of Geophysical Research-Atmospheres,2006,111:D16111.
[20]Creyssels M,Dupont P,Ould El Moctar A,et al.Saltating particles in a turbulent boundary layer:experiment and theory[J].Journal of Fluid Mechanics,2009,625:47-74.
[21]佟鼎,黄宁.天然混合沙运动速度特征的风洞PIV实验[J].工程力学,2011,28(7):229-237.