风沙流和净风场中瞬时水平风速廓线特征比较
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摘要
为进一步认识风沙流和净风场中瞬时水平风速廓线特征的异同,在风洞中分别对风沙流和净风场中瞬时水平风速廓线进行了测量,风速采集时间间隔缩短至0.01s,分析了风沙流和净风场中瞬时水平风速、瞬时摩阻风速和瞬时空气动力学粗糙度的变化特征。结果表明:相同来流条件下,风沙流中水平风速脉动强度高于净风场,风沙流中瞬时摩阻风速、瞬时空气动力学粗糙度以及它们的脉动幅度均大于净风场;风沙流和净风场中瞬时摩阻风速概率密度分布均可以表示为正态分布,但其正态分布的特征值却存在一定差别;净风场中瞬时空气动力学粗糙度的概率密度分布表现出单调递减分布,而风沙流中瞬时空气动力学粗糙度的概率密度分布呈现出单峰分布。因此,在相同主流风速下风沙流和净风场中瞬时水平风速廓线特征有明显差别。
In order to further understand the instantaneous horizontal wind velocity profile characteristics in aeolian sand transport and clean air,the instantaneous horizontal wind velocity profiles were measured in wind tunnel with sampling time interval of 0.01 s.The characteristics of instantaneous horizontal wind velocity,instantaneous friction velocity and instantaneous aerodynamic roughness in aeolian sand transport and clear air are analyzed.The results show that in the same free-stream wind velocity,the horizontal wind velocity fluctuation intensity in windblown sand movement is stronger than that in clear air.The instantaneous friction velocity,instantaneous aerodynamic roughness and their fluctuation in aeolian sand transport are more than that in clear air.The probability density distribution of instantaneous friction velocity both in aeolian sand transport and clear air obeys the normal distribution,while their eigenvalue is different.The probability density distribution of instantaneous aerodynamic roughness in clear air shows a monotone decreasing distribution,while in aeolian sand transport,a single peak appears in the probability density distribution of instantaneous aerodynamic roughness.Therefore,in the same free-stream wind velocity,the characteristics of instantaneous horizontal wind velocity profile in aeolian sand transport and clean air show an obvious distinction.
In order to further understand the instantaneous horizontal wind velocity profile characteristics in aeolian sand transport and clean air,the instantaneous horizontal wind velocity profiles were measured in wind tunnel with sampling time interval of 0.01 s.The characteristics of instantaneous horizontal wind velocity,instantaneous friction velocity and instantaneous aerodynamic roughness in aeolian sand transport and clear air are analyzed.The results show that in the same free-stream wind velocity,the horizontal wind velocity fluctuation intensity in windblown sand movement is stronger than that in clear air.The instantaneous friction velocity,instantaneous aerodynamic roughness and their fluctuation in aeolian sand transport are more than that in clear air.The probability density distribution of instantaneous friction velocity both in aeolian sand transport and clear air obeys the normal distribution,while their eigenvalue is different.The probability density distribution of instantaneous aerodynamic roughness in clear air shows a monotone decreasing distribution,while in aeolian sand transport,a single peak appears in the probability density distribution of instantaneous aerodynamic roughness.Therefore,in the same free-stream wind velocity,the characteristics of instantaneous horizontal wind velocity profile in aeolian sand transport and clean air show an obvious distinction.
引文
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[2]包慧娟,李振山.风沙流中风速纵向脉动的实验研究[J].中国沙漠,2004,24(2):244-247.
[3]王萍,郑晓静.非平稳风沙运动研究进展[J].地球科学进展,2014,29(7):786-794.
[4]张克存,屈建军,俎瑞平,等.典型下垫面风沙流中风速脉动特征研究[J].中国科学D辑:地球科学,2006,36(12):1163-1169.
[5]李振山,倪晋仁.风沙流中风速脉动的实验测量[J].应用基础与工程科学学报,2003,11(4):352-360.
[6]Butterfield G R.Transitional behaviour of saltation:wind tunnel observations of unsteady winds[J].Journal of Arid Environments,1998,39:377-394.
[7]Bauer B O,Yi J,Namikas S L,et al.Event detection and conditional averaging in unsteady aeolian systems[J].Journal of Arid Environments,1998,39:345-375.
[8]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.
[9]Leenders J K,van Boxel J H,Sterk G.Wind forces and related saltation transport[J].Geomorphology,2005,71:357-372.
[10]Butterfield G R.Grain transport rates in steady and unsteady turbulent airflows[J].Acta Mechanica,1991(sup1):97-122.
[11]Liu J,Wang Y,Yang B.Wavelet packet analysis of particle response to turbulent fluctuation[J].Advanced Powder Technology,2012,23:305-314.
[12]Sterk G,Jacobs A F G,Van Boxel J H.The effect of turbulent flow structures on saltation sand transport in the atmospheric boundary layer[J].Earth Surface Processes and Landforms,1998,23:877-887.
[13]张克存,屈建军,董治宝,等.风沙流中风速脉动对输沙量的影响[J].中国沙漠,2006,26(3):336-340.
[14]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.
[15]Pfeifer S,Sch9nfeldt H-J.The response of saltation to wind speed fluctuations[J].Earth Surface Processes and Landforms,2012,37:1056-1064.
[16]Stout J E,Zobeck T M.Intermittent saltation[J].Sedimentology,1997,44:959-970.
[17]Ellis J T.Coherent structures and aeolian saltation[D].Texas,USA:Texas A&M University,2006.
[18]MeKenna-Neuman C,Nickling W G.Momentum extraction with saltation:implications for experimental evaluation of wind profile parameters[J].Boundary-Layer Meteorology,1994,68:35-50.