摘要
通过野外观测与室内风洞实验模拟，结合研究区气象资料统计分析，研究了塔克拉玛干沙漠中部地区线形沙丘表面动力学过程。结果表明，塔克拉玛干沙漠中部地区的线形沙丘与主风向的夹角为１２．５°，与年合成输沙方向（ＲＤＤ）的夹角为４．８°。年合成风向与主风向一致，但风向变率较大。风洞模拟实验揭示，当风向与线形沙丘的夹角较小时，沙丘背风侧均有旁侧气流存在，且随夹角增大而减弱。气流与输沙势分解结果显示，由于平行于沙丘的输沙分量显著大于垂直于沙丘的输沙分量，使线形沙丘纵向移动较快，约为１０ｍ·ａ－１。整体侧向移动不明显，但因风向变率较大，沙丘基座以上局部侧向移动频繁；平行于沙丘的气流分量大于垂直于沙丘的分量，加上背风侧旁侧气流盛行，使沙粒的总体运动方向平行于沙丘的走向方向，从而使线形沙丘在快速纵向移动的过程中保持形态基本不变。
Linear dunes in the central Taklimakan Desert are mainly distributed in the interdunes of compound longitudinal sand ridges. With the exploration and exploitation of oil and natur al gas, the oil highway and buildings which are located in the interdunes where linear dunes dominate, are being threatened seriously by the sands from linear dunes elongation. The dynamic process is the crux of understanding the formati on and development of linear dunes and can provide the theoretical found of engi neering design for the prevention of sand hazards caused by linear dunes. According to field investigation, the linear dunes in central Taklimakan Desert average 400￣500 m long, 3￣10 m wide and 3￣5 m high with the maximum length of mo re than 2 000 m. The average trend of linear dunes is N55°E. Meterological obse rvation shows that the prevailing wind in central Taklimakan Desert is ENE(N67 5°E), when crossing at the southeast side of linear dunes there is an oblique a ngle of 1 2.5° to the linear dunes. The secondary winds of relatively high frequency are NNE, NE on northwest side of linear dunes and E,ESE on southeast side. The annua l resultant wind direction is N67 7°E, which is almost the same as the directi on of the dominant wind(N67 5°E). But the variability of wind direction is pro minent: RDP/DP =0 58. The annual resultant drift direction( RDD ) is 239 8°(N59 8°E), in dicating that the linear dunes in central Taklimakan Desert are typical longitud inal du nes according to their dynamic definition. Tunnel experiments imply that the de flected flow on the leeside almost constantly exists when the wind is oblique to a linear dune. And the deflected flow decreases with the increase of the acute incidence angles.Because of the deviation of air flow after it reaches the top o f linear dunes, lower wind velocity is observed above the upper leeside than tha t near the attachment. If air flow and resultant drift po tential (RDP ) are resolved into two sections which are parallel and perpendic ular, respectively, to the dune crest, the parallel ones are both much more than the perpendicular ones because of low incidence angles between the wind directi on and linear dunes trend. Such air flow, therefore, causes the grains on both windward and lee sides moving along the crest direction, which will maintain th e longitudinal form of dunes. The RDP , however, gives reason why linear dune s elongate rapidly(about 10 m\5a -1 ) during the windy season. In contrast, t he whole lateral migration of linear dunes in this area is not distinct probably because of the significant variability of wind direction which may has caused reverse lateral migration. But the local lateral migration above the dune base is freque ntly observed. Wind regime indicates that the formation of linear dunes in cent ral Taklimakan Desert does not agree with the theory of bidirection wind. Severa l or more crescent dunes in alignment exist at the upwind ends of linear dunes, which may have suggested that the linear dunes in central Taklimakan Desert hav e closer relationships with barchan dunes in formation.This had been demonstrate d by B agnold(1954).
出处
《中国沙漠》
CSCD
北大核心
1999年第2期128-133,共6页
Journal of Desert Research
基金
国家"八五"攻关项目
国家自然基金
